Articoli di riviste: "AI-2"

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Nitta, Hajime Yoshinoand Katsumi. "AI and Law (2)". Journal of Advanced Computational Intelligence and Intelligent Informatics 2, n. 1 (20 febbraio 1998): 1. http://dx.doi.org/10.20965/jaciii.1998.p0001.

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In the last issue (Vol.1, No.2), we introduced the Legal Expert System (LES) project led by Hajime Yoshino of Meiji Gakuin University, presenting six papers on the LES project. Those papers were mainly related to higher order reasoning systems such as ase-based reasoning, abductive and inductive logic programming, nonmonotonic reasoning, and analogical reasoning. The objective of the LES project was to develop a legal expert system effective for use by lawyers, so the project covers inference mechanisms, analysis of legal knowledge, and user interfaces. In this second special issue on the LES project, we present five more papers, mainly related to the analysis of legal knowledge, legal knowledge representation language, and legal reasoning system user interfaces. Hajime Yoshino analyzes the logical structure of contract law. To develop a knowledge base for the United Nations Convention on Contracts for the International Sale of Goods (CISG), he proposes a clear logical model of the contract law system, which treats relations between events and legal status such as rights and obligations. Yoshino demonstrates that legal metarules are effective in constructing deductive legal reasoning systems, and are appropriate from the viewpoint of jurisprudence. Seiichiro Sakurai discusses the logical features of the legal knowledge representation language, CPF, developed by Hajime Yoshino. CPF is a logic programming language that enhances the representation of complex data structures. CPF is a convenient tool for representing legal knowledge, yet lawyers often attempt to describe nonexecutable forms of CPF rules.Sakurai introduces a way to construct an executable knowledge base from lawyers' CPF rules. Masato Shibasaki and Katsumi Nitta introduce a new framework to formalize nonmonotonic reasoning with dynamic priorities. The several frameworks proposed thus far to model relationships among arguments do not treat complex arguments, composed of strict rules and default rules. They show that the new framework represents such relationships and analyze these relationships for this framework and others. Takashi Miyata and Yuji Matsumoto introduce LES natural language generation using a user interface for lawyers rather than computer scientists. They describe a sentence generation system that translates logical forms provided from an inference engine into natural-language sentences, and present the unification grammar, generation algorithm and graphical debugging tool. To develop a knowledge base, the lawyers of the LES project analyze and represents the relationships between requirements (actions or events) and consequences (legal status) of legal rules in the form of logical flowcharts. Once the appropriateness of a flowchart is confirmed, they convert it to a CPF rule in their knowledge base. Koji Miyagi, Motoki Miura and Jiro Tanaka developed a flowchart editor that makes legal flowcharting easier. To make it easier to decide where to locate flowchart components and draw linens between the components, the editor possesses several algorithms.

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Eaton, Eric, e Amy McGovern. "Welcome to AI Matters, volume 2, issue 2". AI Matters 2, n. 2 (11 gennaio 2016): 3. http://dx.doi.org/10.1145/2847557.2847558.

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McGovern, Amy, e Iolanda Leite. "Welcome to AI matters 5(2)". AI Matters 5, n. 2 (5 agosto 2019): 3. http://dx.doi.org/10.1145/3340470.3340471.

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Leite, Iolanda, e Anuj Karpatne. "Welcome to AI matters 6(2)". AI Matters 6, n. 2 (4 gennaio 2021): 3–4. http://dx.doi.org/10.1145/3430581.3430582.

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Pereira, Catarina S., Jessica A. Thompson e Karina B. Xavier. "AI-2-mediated signalling in bacteria". FEMS Microbiology Reviews 37, n. 2 (marzo 2013): 156–81. http://dx.doi.org/10.1111/j.1574-6976.2012.00345.x.

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McGovern, Amy. "Welcome to AI matters 4(2)". AI Matters 4, n. 2 (30 luglio 2018): 3–4. http://dx.doi.org/10.1145/3236644.3236645.

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Wagstaff, Kiri. "Welcome to AI Matters Issue 2". AI Matters 1, n. 2 (19 dicembre 2014): 3. http://dx.doi.org/10.1145/2685328.2685329.

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Esuli, Andrea, Fabrizio Sebastiani e Ahmed Abasi. "AI and Opinion Mining, Part 2". IEEE Intelligent Systems 25, n. 4 (luglio 2010): 72–79. http://dx.doi.org/10.1109/mis.2010.94.

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Leite, Iolanda, e Anuj Karpatne. "Welcome to AI Matters 7(2)". AI Matters 7, n. 2 (giugno 2021): 3–4. http://dx.doi.org/10.1145/3478369.3478370.

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Welcome to the second issue of this year's AI Matters Newsletter. We start with a report on upcoming SIGAI Events by Dilini Samarasinghe and Conference reports by Louise Dennis, our conference coordination officer. In our regular Education column, Carolyn Rosé discusses the role of AI in education in a post-pandemic reality. We then bring you our regular Policy column, where Larry Medsker covers interesting and timely discussions on AI policy, for example whether governments should play a role in reducing algorithmic bias. This issue closes with an article contribution from Li Dong, one of the runner-ups in the latest AAIS/SIGAI dissertation award, on the use neural models to build natural language interfaces.

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Pereira, Catarina S., J. Randall McAuley, Michiko E. Taga, Karina B. Xavier e Stephen T. Miller. "Sinorhizobium meliloti, a bacterium lacking the autoinducer-2 (AI-2) synthase, responds to AI-2 supplied by other bacteria". Molecular Microbiology 70, n. 5 (dicembre 2008): 1223–35. http://dx.doi.org/10.1111/j.1365-2958.2008.06477.x.

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Sakurai, Emiko, e Murakami Ryu. "Ai to gensō no fashizumu. 2 vols". World Literature Today 63, n. 1 (1989): 165. http://dx.doi.org/10.2307/40145289.

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Pereira, Catarina S., Anna K. de Regt, Patrícia H. Brito, Stephen T. Miller e Karina B. Xavier. "Identification of Functional LsrB-Like Autoinducer-2 Receptors". Journal of Bacteriology 191, n. 22 (11 settembre 2009): 6975–87. http://dx.doi.org/10.1128/jb.00976-09.

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ABSTRACT Although a variety of bacterial species have been reported to use the interspecies communication signal autoinducer-2 (AI-2) to regulate multiple behaviors, the molecular mechanisms of AI-2 recognition and signal transduction remain poorly understood. To date, two types of AI-2 receptors have been identified: LuxP, present in Vibrio spp., and LsrB, first identified in Salmonella enterica serovar Typhimurium. In S. Typhimurium, LsrB is the ligand binding protein of a transport system that enables the internalization of AI-2. Here, using both sequence analysis and structure prediction, we establish a set of criteria for identifying functional AI-2 receptors. We test our predictions experimentally, assaying key species for their abilities to import AI-2 in vivo, and test their LsrB orthologs for AI-2 binding in vitro. Using these experimental approaches, we were able to identify AI-2 receptors in organisms belonging to phylogenetically distinct families such as the Enterobacteriaceae, Rhizobiaceae, and Bacillaceae. Phylogenetic analysis of LsrB orthologs indicates that this pattern could result from one single origin of the functional LsrB gene in a gammaproteobacterium, suggesting possible posterior independent events of lateral gene transfer to the Alphaproteobacteria and Firmicutes. Finally, we used mutagenesis to show that two AI-2-interacting residues are essential for the AI-2 binding ability. These two residues are conserved in the binding sites of all the functional AI-2 binding proteins but not in the non-AI-2-binding orthologs. Together, these results strongly support our ability to identify functional LsrB-type AI-2 receptors, an important step in investigations of this interspecies signal.

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Marques, João C., Pedro Lamosa, Caitlin Russell, Rita Ventura, Christopher Maycock, Martin F. Semmelhack, Stephen T. Miller e Karina B. Xavier. "Processing the Interspecies Quorum-sensing Signal Autoinducer-2 (AI-2)". Journal of Biological Chemistry 286, n. 20 (30 marzo 2011): 18331–43. http://dx.doi.org/10.1074/jbc.m111.230227.

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Shao, Hanjuan, Deanna James, Richard J. Lamont e Donald R. Demuth. "Differential Interaction of Aggregatibacter (Actinobacillus) actinomycetemcomitans LsrB and RbsB Proteins with Autoinducer 2". Journal of Bacteriology 189, n. 15 (25 maggio 2007): 5559–65. http://dx.doi.org/10.1128/jb.00387-07.

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ABSTRACT Our previous studies showed that the Aggregatibacter actinomycetemcomitans RbsB protein interacts with cognate and heterologous autoinducer 2 (AI-2) signals and suggested that the rbsDABCK operon encodes a transporter that may internalize AI-2 (D. James et al., Infect. Immun. 74:4021-4029, 2006.). However, A. actinomycetemcomitans also possesses genes related to the lsr operon of Salmonella enterica serovar Typhimurium which function to import AI-2. Here, we show that A. actinomycetemcomitans LsrB protein competitively inhibits the interaction of the Vibrio harveyi AI-2 receptor (LuxP) with AI-2 from either A. actinomycetemcomitans or V. harveyi. Interestingly, LsrB was a more potent inhibitor of LuxP interaction with AI-2 from V. harveyi whereas RbsB competed more effectively with LuxP for A. actinomycetemcomitans AI-2. Inactivation of lsrB in wild-type A. actinomycetemcomitans or in an isogenic RbsB-deficient strain reduced the rate by which intact bacteria depleted A. actinomycetemcomitans AI-2 from solution. Consistent with the results from the LuxP competition experiments, the LsrB-deficient strain depleted AI-2 to a lesser extent than the RbsB-deficient organism. Inactivation of both lsrB and rbsB virtually eliminated the ability of the organism to remove AI-2 from the extracellular environment. These results suggest that A. actinomycetemcomitans possesses two proteins that differentially interact with AI-2 and may function to inactivate or facilitate internalization of AI-2.

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Yu, Jing, Melissa L. Madsen, Michael D. Carruthers, Gregory J. Phillips, Jeffrey S. Kavanaugh, Jeff M. Boyd, Alexander R. Horswill e F. Chris Minion. "Analysis of Autoinducer-2 Quorum Sensing in Yersinia pestis". Infection and Immunity 81, n. 11 (19 agosto 2013): 4053–62. http://dx.doi.org/10.1128/iai.00880-13.

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ABSTRACTThe autoinducer-2 (AI-2) quorum-sensing system has been linked to diverse phenotypes and regulatory changes in pathogenic bacteria. In the present study, we performed a molecular and biochemical characterization of the AI-2 system inYersinia pestis, the causative agent of plague. In strain CO92, the AI-2 signal is produced in aluxS-dependent manner, reaching maximal levels of 2.5 μM in the late logarithmic growth phase, and both wild-type and pigmentation (pgm) mutant strains made equivalent levels of AI-2. Strain CO92 possesses a chromosomallsrlocus encoding factors involved in the binding and import of AI-2, and confirming this assignment, anlsrdeletion mutant increased extracellular pools of AI-2. To assess the functional role of AI-2 sensing inY. pestis, microarray studies were conducted by comparing Δpgmstrain R88 to a ΔpgmΔluxSmutant or a quorum-sensing-null ΔpgmΔypeIRΔyspIRΔluxSmutant at 37°C. Our data suggest that AI-2 quorum sensing is associated with metabolic activities and oxidative stress genes that may helpY. pestissurvive at the host temperature. This was confirmed by observing that theluxSmutant was more sensitive to killing by hydrogen peroxide, suggesting a potential requirement for AI-2 in evasion of oxidative damage. We also show that a large number of membrane protein genes are controlled by LuxS, suggesting a role for quorum sensing in membrane modeling. Altogether, this study provides the first global analysis of AI-2 signaling inY. pestisand identifies potential roles for the system in controlling genes important to disease.

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Wang, Yang, Li Yi, Zhicheng Zhang, Hongjie Fan, Xiangchao Cheng e Chengping Lu. "Overexpression ofluxSCannot Increase Autoinducer-2 Production, Only Affect the Growth and Biofilm Formation inStreptococcus suis". Scientific World Journal 2013 (2013): 1–6. http://dx.doi.org/10.1155/2013/924276.

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LuxS/AI-2 quorum sensing (QS) system involves the production of cell signaling molecules vialuxS-based autoinducer-2 (AI-2). LuxS has been reported to plays critical roles in regulating various behaviors of bacteria. AI-2 is a byproduct of the catabolism of S-adenosylhomocysteine (SAH) performed by the LuxS and Pfs enzymes. In our previous study, the function of LuxS in AI-2 production was verified inStreptococcus suis(SS). Decreased levels of SS biofilm formation and host-cell adherence as well as an inability to produce AI-2 were observed in bacteria having aluxSmutant gene. In this study, the level of AI-2 activity exhibits a growth-phase dependence with a maximum in late exponential culture in SS. An SS strain that overexpressedluxSwas constructed to comprehensively understand the function of AI-2. OverexpressedluxSwas not able to increase the level ofpfsexpression and produce additional AI-2, and the bacteria were slower growing and produced only slightly more biofilm than the wild type. Thus, AI-2 production is not correlated withluxStranscription.luxSexpression is constitutive, but the transcription ofpfsis perhaps correlated with AI-2 production in SS.

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Wanaldi, Wanaldi, Yustinus Eko Sulistio e Johan Setiawan. "DynaBot: Dynamic Dota 2 Bot". IJNMT (International Journal of New Media Technology) 7, n. 1 (2 luglio 2020): 11–17. http://dx.doi.org/10.31937/ijnmt.v7i1.1695.

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This research was conducted to find out whether the Dynamic Scripting method that has been used before only on zeus characters can be generalized to be used on other characters on the Dota 2 game. Dynamic scripting works by using the rulebase where the rulebase contains actions that determine the actions performed by Artificial Intelligence (AI). In addition, some adjustments have been made to existing methods. To find out whether the performance of a generalized and adjusted model is better than the previous model, a test has been conducted where AI is made with dynamic scripting against AI provided by the valve in the Dota 2 game. In addition, AI has also been tested against humans. Then the performance of AI will be analyzed by comparing the winning ratio and several other supporting variables. The results of this study are that AI got a low winning percentage against standard AI and cannot win at all and give poor performance against humans. It can be concluded that the Dynamic Scripting method cannot be generalized to other characters in the Dota 2 game.

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De Keersmaecker, Sigrid C. J., Kathleen Sonck e Jos Vanderleyden. "Let LuxS speak up in AI-2 signaling". Trends in Microbiology 14, n. 3 (marzo 2006): 114–19. http://dx.doi.org/10.1016/j.tim.2006.01.003.

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Eaton, Eric, e Amy McGovern. "Welcome to AI matters, volume 3, issue 2". AI Matters 3, n. 2 (13 luglio 2017): 3. http://dx.doi.org/10.1145/3098888.3098889.

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Li, Min, Amer E. Villaruz, Viveka Vadyvaloo, Daniel E. Sturdevant e Michael Otto. "AI-2-dependent gene regulation in Staphylococcus epidermidis". BMC Microbiology 8, n. 1 (2008): 4. http://dx.doi.org/10.1186/1471-2180-8-4.

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Eaton, Eric, e Amy McGovern. "Welcome to AI Matters, volume 2, issue 3". AI Matters 2, n. 3 (21 giugno 2016): 3. http://dx.doi.org/10.1145/2911172.2911173.

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Wang, Yang, Yuxin Wang, Liyun Sun, Daniel Grenier e Li Yi. "The LuxS/AI-2 system of Streptococcus suis". Applied Microbiology and Biotechnology 102, n. 17 (25 giugno 2018): 7231–38. http://dx.doi.org/10.1007/s00253-018-9170-7.

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James, DeAnna, HanJuan Shao, Richard J. Lamont e Donald R. Demuth. "The Actinobacillus actinomycetemcomitans Ribose Binding Protein RbsB Interacts with Cognate and Heterologous Autoinducer 2 Signals". Infection and Immunity 74, n. 7 (luglio 2006): 4021–29. http://dx.doi.org/10.1128/iai.01741-05.

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ABSTRACT Autoinducer 2 (AI-2) produced by the oral pathogen Actinobacillus actinomycetemcomitans influences growth of the organism under iron limitation and regulates the expression of iron uptake genes. However, the cellular components that mediate the response of A. actinomycetemcomitans to AI-2 have not been fully characterized. Analysis of the complete genome sequence of A. actinomycetemcomitans (www.oralgen.lanl.gov ) indicated that the RbsB protein was related to LuxP, the AI-2 receptor of Vibrio harveyi. To determine if RbsB interacts with AI-2, the bioluminescence of the reporter strain V. harveyi BB170 (sensor 1−, sensor 2+) was determined after stimulation with partially purified AI-2 from A. actinomycetemcomitans or conditioned medium from V. harveyi cultures in the presence and absence of purified six-His-tagged RbsB. RbsB efficiently inhibited V. harveyi bioluminescence induced by both A. actinomycetemcomitans AI-2 and V. harveyi AI-2 in a dose-dependent manner, suggesting that RbsB competes with LuxP for AI-2. Fifty percent inhibition occurred with approximately 0.3 nM RbsB for A. actinomycetemcomitans AI-2 and 15 nM RbsB for V. harveyi AI-2. RbsB-mediated inhibition of V. harveyi bioluminescence was reversed by the addition of 50 mM ribose, suggesting that A. actinomycetemcomitans AI-2 and ribose bind at the same site of RbsB. The RbsB/AI-2 complex was thermostable since A. actinomycetemcomitans AI-2 could not be recovered by heating. This was not due to heat inactivation of A. actinomycetemcomitans AI-2 since signal activity was unaffected by heating in the absence of RbsB. Furthermore, an isogenic A. actinomycetemcomitans mutant that was unable to express rbsB was deficient in depleting A. actinomycetemcomitans AI-2 from solution relative to the wild-type organism. Inactivation of rbsB also influenced the ability of the organism to grow under iron-limiting conditions. The mutant strain attained a cell density of approximately 30% that of the wild-type organism under iron limitation. In addition, real-time PCR showed that the expression of afuABC, encoding a major ferric ion transporter, was reduced by approximately eightfold in the rbsB mutant. This phenotype was similar to that of a LuxS-deficient mutant of A. actinomycetemcomitans that is unable to produce AI-2. Together, our results suggest that RbsB may play a role in the response of A. actinomycetemcomitans to AI-2.

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Hegde, M., D. L. Englert, S. Schrock, W. B. Cohn, C. Vogt, T. K. Wood, M. D. Manson e A. Jayaraman. "Chemotaxis to the Quorum-Sensing Signal AI-2 Requires the Tsr Chemoreceptor and the Periplasmic LsrB AI-2-Binding Protein". Journal of Bacteriology 193, n. 3 (19 novembre 2010): 768–73. http://dx.doi.org/10.1128/jb.01196-10.

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Liu, Yirong, Huizhi Hu e Feng Luo. "Roles of autoinducer-2 mediated quorum sensing in wastewater treatment". Water Science and Technology 84, n. 4 (16 luglio 2021): 793–809. http://dx.doi.org/10.2166/wst.2021.278.

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Abstract Quorum sensing (QS) is considered to be a promising regulation method for biological wastewater treatment (WWT) due to its regulation in extracellular substances (EPS) production, biofilm formation, granulation, colonization and bacterial activity and stability. Recently, autoinducer-2 (AI-2), a kind of interspecies communication QS signal molecule, is being increasingly reported for its roles in regulating bacterial gene expression and aggregation. Consequently, AI-2 mediated QS system is considered as a promising regulatory approach in WWT processes. This article systematically reviews the effects of AI-2-mediated QS system on bacterial behavior and its high potential for real-world applications in different WWT systems. Given the extensive presence of AI-2, AI-2 mediated QS could cooperate with other signal molecules in WWT processes, which suggests that the interactions among multiple signal molecules might be underestimated in the previous studies. The differences between AI-2 and AHL signaling molecules are also compared. Furthermore, the attempts at AI-2 regulated QS in pollution control of different WWT systems are summarized, while some challenges and defects still require targeted research in the future.

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Krin, Evelyne, Nesrine Chakroun, Evelyne Turlin, Alain Givaudan, François Gaboriau, Isabelle Bonne, Jean-Claude Rousselle et al. "Pleiotropic Role of Quorum-Sensing Autoinducer 2 in Photorhabdus luminescens". Applied and Environmental Microbiology 72, n. 10 (ottobre 2006): 6439–51. http://dx.doi.org/10.1128/aem.00398-06.

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ABSTRACT Bacterial virulence is an integrative process that may involve quorum sensing. In this work, we compared by global expression profiling the wild-type entomopathogenic Photorhabdus luminescens subsp. laumondii TT01 to a luxS-deficient mutant unable to synthesize the type 2 quorum-sensing inducer AI-2. AI-2 was shown to regulate more than 300 targets involved in most compartments and metabolic pathways of the cell. AI-2 is located high in the hierarchy, as it controls the expression of several transcriptional regulators. The regulatory effect of AI-2 appeared to be dose dependent. The luxS-deficient strain exhibited decreased biofilm formation and increased type IV/V pilus-dependent twitching motility. AI-2 activated its own synthesis and transport. It also modulated bioluminescence by regulating the synthesis of spermidine. AI-2 was further shown to increase oxidative stress resistance, which is necessary to overcome part of the innate immune response of the host insect involving reactive oxygen species. Finally, we showed that the luxS-deficient strain had attenuated virulence against the lepidopteran Spodoptera littoralis. We concluded that AI-2 is involved mainly in early steps of insect invasion in P. luminescens.

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LU, LINGENG, MICHAEL E. HUME e SURESH D. PILLAI. "Autoinducer-2–like Activity Associated with Foods and Its Interaction with Food Additives". Journal of Food Protection 67, n. 7 (1 luglio 2004): 1457–62. http://dx.doi.org/10.4315/0362-028x-67.7.1457.

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The autoinducer-2 (AI-2) molecule produced by bacteria as part of quorum sensing is considered to be a universal inducer signal in bacteria because it reportedly influences gene expression in a variety of both gram-negative and gram-positive bacteria. The objective of this study was to determine whether selected fresh produce and processed foods have AI-2–like activity and whether specific food additives can act as AI-2 mimics and result in AI-2–like activity. The luminescence-based response of the reporter strain Vibrio harveyi BB170 was used as the basis for determining AI-2 activity in the selected foods and food ingredients. Maximum AI-2 activity was seen on the frozen fish sample (203-fold, compared with the negative control) followed by tomato, cantaloupe, carrots, tofu, and milk samples. Interestingly, some samples were capable of inhibiting AI-2 activity. Turkey patties showed the highest inhibition (99.8% compared with the positive control) followed by chicken breast (97.5%), homemade cheeses (93.7%), beef steak (90.6%), and beef patties (84.4%). AI-2 activity was almost totally inhibited by sodium propionate, whereas sodium benzoate caused 93.3% inhibition, compared with 75% inhibition by sodium acetate. Sodium nitrate did not have any appreciable effect, even at 200 ppm. Understanding the relationships that exist between AI-2 activity on foods and the ecology of pathogens and food spoilage bacteria on foods could yield clues about factors controlling food spoilage and pathogen virulence.

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SONI, KAMLESH A., PALMY JESUDHASAN, MARTHA CEPEDA, KENNETH WIDMER, G. K. JAYAPRAKASHA, BHIMANAGOUDA S. PATIL, MICHAEL E. HUME e SURESH D. PILLAI. "Identification of Ground Beef–Derived Fatty Acid Inhibitors of Autoinducer-2–Based Cell Signaling". Journal of Food Protection 71, n. 1 (1 gennaio 2008): 134–38. http://dx.doi.org/10.4315/0362-028x-71.1.134.

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Autoinducer-2 (AI-2) molecules are used by several microorganisms to modulate various processes, including bioluminescence, biofilm formation, and virulence expression. Certain food matrices, including ground beef extracts, possess compounds capable of inhibiting AI-2 activity. In the present study, we identified and characterized these AI-2 inhibitors from ground beef extract using hexane solvent extraction and gas chromatography. Gas chromatographic analysis revealed the presence of several fatty acids such as palmitic acid (C16:0), stearic acid (C18:0), oleic acid (C18:1ω9), and linoleic acid (C18:2ω6) that were capable of inhibiting AI-2 activity. These fatty acids were tested (using Vibrio harveyi BB170 and MM32 reporter strains) at different concentrations (1, 5, and 10 mM) to identify differences in the level of AI-2 activity inhibition. AI-2 inhibition ranged from 25 to 90%. A mixture of these fatty acids (prepared at concentrations equivalent to those present in the ground beef extract) produced 52 to 65% inhibition of AI-2 activity. The fatty acid mixture also negatively influenced Escherichia coli K-12 biofilm formation. These results demonstrate that both medium- and long-chain fatty acids in ground beef have the ability to interfere with AI-2–based cell signaling.

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Khodayari, Khosro, Roy J. Smith e Howard L. Black. "Red Rice (Oryza sativa) Control with Herbicide Treatments in Soybeans (Glycine max)". Weed Science 35, n. 1 (gennaio 1987): 127–29. http://dx.doi.org/10.1017/s0043174500026916.

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Preplant incorporation of alachlor [2-chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl)acetamide] at 3.6 kg ai/ha, metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] at 2.2 kg ai/ha, and tank mixtures of imazaquin {2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid} with either alachlor at 0.14 + 2.2 kg ai/ha or metolachlor at 0.14 + 1.1 kg ai/ha controlled >90% red rice (Oryza sativaL. # ORYSA) in soybeans [Glycine max(L.) Merr.]. Also, FMC-57020 [2-(2-chlorophenyl)methyl-4,4-dimethyl-3-isoxazolidinone] at 1.7 kg ai/ha applied preplant incorporated controlled > 80% of the red rice. DPX-Y6202 {2-[4-[(6-chloro-2-quinoxalinyl)oxy]-phenoxy]-propionic acid, ethyl ester} was the best and most consistent postemergence herbicide treatment for red rice control when applied once at 0.28 kg ai/ha or sequentially at 0.14 kg ai/ha each time. Haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl]oxy] phenoxy] propanoic acid} applied at 0.16 kg ai/ha followed by another application at 0.14 kg ai/ha gave excellent red rice control in 2 of 3 years. Soybeans were uninjured by the herbicide treatments and yield was higher from treated than untreated soybeans.

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Song, Sooyeon, e Thomas K. Wood. "The Primary Physiological Roles of Autoinducer 2 in Escherichia coli Are Chemotaxis and Biofilm Formation". Microorganisms 9, n. 2 (14 febbraio 2021): 386. http://dx.doi.org/10.3390/microorganisms9020386.

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Autoinducer 2 (AI-2) is a ubiquitous metabolite but, instead of acting as a “universal signal,” relatively few phenotypes have been associated with it, and many scientists believe AI-2 is often a metabolic byproduct rather than a signal. Here, the aim is to present evidence that AI-2 influences both biofilm formation and motility (swarming and chemotaxis), using Escherichia coli as the model system, to establish AI-2 as a true signal with an important physiological role in this bacterium. In addition, AI-2 signaling is compared to the other primary signal of E. coli, indole, and it is shown that they have opposite effects on biofilm formation and virulence.

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BLANA, VASILIKI A., AGAPI I. DOULGERAKI e GEORGE-JOHN E. NYCHAS. "Autoinducer-2–like Activity in Lactic Acid Bacteria Isolated from Minced Beef Packaged under Modified Atmospheres". Journal of Food Protection 74, n. 4 (1 aprile 2011): 631–35. http://dx.doi.org/10.4315/0362-028x.jfp-10-276.

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Fifteen fingerprints (assigned to Leuconostoc spp., Leuconostoc mesenteroides, Weissella viridescens, Leuconostoc citreum, and Lactobacillus sakei) of 89 lactic acid bacteria (LAB) isolated from minced beef stored under modified atmospheres at various temperatures were screened for their ability to exhibit autoinducer-2 (AI-2)–like activity under certain growth conditions. Cell-free meat extracts (CFME) were collected at the same time as the LAB isolates and tested for the presence of AI-2–like molecules. All bioassays were conducted using the Vibrio harveyi BAA-1117 (sensor 1−, sensor 2+) biosensor strain. The possible inhibitory effect of meat extracts on the activity of the biosensor strain was also evaluated. AI-2–like activity was observed for Leuconostoc spp. isolates, but none of the L. sakei strains produced detectable AI-2–like activity. The AI-2–like activity was evident mainly associated with the Leuconostoc sp. B 233 strain, which was the dominant isolate recovered from storage at 10 and 15°C and at the initial and middle stages of storage at chill temperatures (0 and 5°C). The tested CFME samples displayed low AI-2–like activity and inhibited AI-2 activity regardless of the indigenous bacterial populations. The LAB isolated during meat spoilage exhibited AI-2–like activity, whereas the LAB strains retrieved depended on storage time and temperature. The production of AI-2–like molecules may affect the dominance of different bacterial strains during storage. The results provide a basis for further research concerning the effect of storage temperature on the expression of genes encoding AI-2 activity and on the diversity of the ephemeral bacterial population.

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Shao, Hanjuan, Richard J. Lamont e Donald R. Demuth. "Autoinducer 2 Is Required for Biofilm Growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans". Infection and Immunity 75, n. 9 (25 giugno 2007): 4211–18. http://dx.doi.org/10.1128/iai.00402-07.

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ABSTRACT Autoinducer 2 (AI-2) is required for the growth of Aggregatibacter (Actinobacillus) actinomycetemcomitans in culture under conditions of iron limitation. However, in vivo this organism thrives in a complex multispecies biofilm that forms in the human oral cavity. In this report, we show that adherent growth of A. actinomycetemcomitans on a saliva-coated surface, but not planktonic growth under iron-replete conditions, is defective in a LuxS-deficient background. Biofilm growth of the luxS mutant exhibited lower total biomass and lower biofilm depth than those for the wild-type strain. Normal biofilm growth of the luxS mutant was restored genetically by introduction of a functional copy of luxS and biochemically by addition of partially purified AI-2. Furthermore, introduction of S-adenosylhomocysteine hydrolase, which restores the metabolism of S-adenosylmethionine in the absence of LuxS, into A. actinomycetemcomitans did not complement the luxS mutation unless AI-2 was added in trans. This suggests that AI-2 itself is required for biofilm growth by A. actinomycetemcomitans. A biofilm growth deficiency similar to that of the LuxS-deficient strain was also observed when a gene encoding the AI-2-interacting protein RbsB or LsrB was inactivated. Biofilm formation by A. actinomycetemcomitans was virtually eliminated upon inactivation of both rbsB and lsrB. In addition, biofilm growth by wild-type A. actinomycetemcomitans was reduced in the presence of ribose, which competes with AI-2 for binding to RbsB. These results suggest that RbsB and LsrB function as AI-2 receptors in A. actinomycetemcomitans and that the development of A. actinomycetemcomitans biofilms requires AI-2.

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Cox, Clayton E., Michael McClelland e Max Teplitski. "Consequences of Disrupting Salmonella AI-2 Signaling on Interactions Within Soft Rots". Phytopathology® 103, n. 4 (aprile 2013): 352–61. http://dx.doi.org/10.1094/phyto-09-12-0237-fi.

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Within soft rots, Salmonella spp. reach population densities 10- to 100-fold higher than within intact plants. The hypothesis that Salmonella spp. exchange AI-2 signals with Pectobacterium carotovorum to increase its competitive fitness was tested using mutants involved in AI-2 production (luxS) or perception (lsrACDBF or lsrG). Co-infections of a wild-type Salmonella sp. and its AI-2 mutants (at ≈3 to 104) were established in green or red tomato (‘FL 47’ or ‘Campari’ for 3 or 5 days) as well as tomato co-infected with Pectobacterium (at 109) or its luxS mutant. There were no significant differences in the competitive fitness of Salmonella, indicating that AI-2 signaling is not a major input in the interactions between these organisms under the tested conditions. A Salmonella lsrG::tnpR-lacZ resolvase in vivo expression technology (RIVET) reporter, constructed to monitor AI-2-related gene expression, responded strongly to the luxS deletion but only weakly to external sources of AI-2. Growth in soft rots generally decreased RIVET resolution; however, the effect was not correlated to the luxS genotype of the Pectobacterium sp. The results of this study show that AI-2 signaling offers no significant benefit to Salmonella spp. in this model of colonization of tomato or soft rots.

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34

Novak, Elizabeth A., HanJuan Shao, Carlo Amorin Daep e Donald R. Demuth. "Autoinducer-2 and QseC Control Biofilm Formation and In Vivo Virulence of Aggregatibacter actinomycetemcomitans". Infection and Immunity 78, n. 7 (19 aprile 2010): 2919–26. http://dx.doi.org/10.1128/iai.01376-09.

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ABSTRACT Biofilm formation by the periodontal pathogen Aggregatibacter actinomycetemcomitans is dependent upon autoinducer-2 (AI-2)-mediated quorum sensing. However, the components that link the detection of the AI-2 signal to downstream gene expression have not been determined. One potential regulator is the QseBC two-component system, which is part of the AI-2-dependent response pathway that controls biofilm formation in Escherichia coli. Here we show that the expression of QseBC in A. actinomycetemcomitans is induced by AI-2 and that induction requires the AI-2 receptors, LsrB and/or RbsB. Additionally, inactivation of qseC resulted in reduced biofilm growth. Since the ability to grow in biofilms is essential for A. actinomycetemcomitans virulence, strains that were deficient in QseC or the AI-2 receptors were examined in an in vivo mouse model of periodontitis. The ΔqseC mutant induced significantly less alveolar bone resorption than the wild-type strain (P < 0.02). Bone loss in animals infected with the ΔqseC strain was similar to that in sham-infected animals. The ΔlsrB, ΔrbsB, and ΔlsrB ΔrbsB strains also induced significantly less alveolar bone resorption than the wild type (P < 0.03, P < 0.02, and P < 0.01, respectively). However, bone loss induced by a ΔluxS strain was indistinguishable from that induced by the wild type, suggesting that AI-2 produced by indigenous microflora in the murine oral cavity may complement the ΔluxS mutation. Together, these results suggest that the QseBC two-component system is part of the AI-2 regulon and may link the detection of AI-2 to the regulation of downstream cellular processes that are involved in biofilm formation and virulence of A. actinomycetemcomitans.

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35

Zhu, Peng, e Minyong Li. "Recent Progresses on AI-2 Bacterial Quorum Sensing Inhibitors". Current Medicinal Chemistry 19, n. 2 (1 gennaio 2012): 174–86. http://dx.doi.org/10.2174/092986712803414187.

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36

Garner, Amanda L., Junguk Park, Joseph S. Zakhari, Colin A. Lowery, Anjali Kumari Struss, Daisuke Sawada, Gunnar F. Kaufmann e Kim D. Janda. "A Multivalent Probe for AI-2 Quorum-Sensing Receptors". Journal of the American Chemical Society 133, n. 40 (12 ottobre 2011): 15934–37. http://dx.doi.org/10.1021/ja207556d.

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37

Xavier, Karina B., e Bonnie L. Bassler. "Interference with AI-2-mediated bacterial cell–cell communication". Nature 437, n. 7059 (settembre 2005): 750–53. http://dx.doi.org/10.1038/nature03960.

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38

Gölz, G., L. Adler, S. Huehn e T. Alter. "LuxS distribution and AI-2 activity of Campylobacter spp." Journal of Applied Microbiology 112, n. 3 (9 gennaio 2012): 571–78. http://dx.doi.org/10.1111/j.1365-2672.2011.05221.x.

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39

Alencar, Valquíria Campos, Juliana de Fátima dos Santos Silva, Renata Ozelami Vilas Boas, Vinícius Manganaro Farnézio, Yara N. L. F. de Maria, David Aciole Barbosa, Alex Tramontin Almeida et al. "The Quorum Sensing Auto-Inducer 2 (AI-2) Stimulates Nitrogen Fixation and Favors Ethanol Production over Biomass Accumulation in Zymomonas mobilis". International Journal of Molecular Sciences 22, n. 11 (26 maggio 2021): 5628. http://dx.doi.org/10.3390/ijms22115628.

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Abstract (sommario):

Autoinducer 2 (or AI-2) is one of the molecules used by bacteria to trigger the Quorum Sensing (QS) response, which activates expression of genes involved in a series of alternative mechanisms, when cells reach high population densities (including bioluminescence, motility, biofilm formation, stress resistance, and production of public goods, or pathogenicity factors, among others). Contrary to most autoinducers, AI-2 can induce QS responses in both Gram-negative and Gram-positive bacteria, and has been suggested to constitute a trans-specific system of bacterial communication, capable of affecting even bacteria that cannot produce this autoinducer. In this work, we demonstrate that the ethanologenic Gram-negative bacterium Zymomonas mobilis (a non-AI-2 producer) responds to exogenous AI-2 by modulating expression of genes involved in mechanisms typically associated with QS in other bacteria, such as motility, DNA repair, and nitrogen fixation. Interestingly, the metabolism of AI-2-induced Z. mobilis cells seems to favor ethanol production over biomass accumulation, probably as an adaptation to the high-energy demand of N2 fixation. This opens the possibility of employing AI-2 during the industrial production of second-generation ethanol, as a way to boost N2 fixation by these bacteria, which could reduce costs associated with the use of nitrogen-based fertilizers, without compromising ethanol production in industrial plants.

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40

Xavier, Karina B., e Bonnie L. Bassler. "Regulation of Uptake and Processing of the Quorum-Sensing Autoinducer AI-2 in Escherichia coli". Journal of Bacteriology 187, n. 1 (1 gennaio 2005): 238–48. http://dx.doi.org/10.1128/jb.187.1.238-248.2005.

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ABSTRACT AI-2 is a quorum-sensing signaling molecule proposed to be involved in interspecies communication. In Escherichia coli and Salmonella enterica serovar Typhimurium, extracellular AI-2 accumulates in exponential phase, but the amount decreases drastically upon entry into stationary phase. In S. enterica serovar Typhimurium, the reduction in activity is due to import and processing of AI-2 by the Lsr transporter. We show that the Lsr transporter is functional in E. coli, and screening for mutants defective in AI-2 internalization revealed lsrK and glpD. Unlike the wild type, lsrK and glpD mutants do not activate transcription of the lsr operon in response to AI-2. lsrK encodes the AI-2 kinase, and the lsrK mutant fails to activate lsr expression because it cannot produce phospho-AI-2, which is the lsr operon inducer. glpD encodes the glycerol-3-phosphate (G3P) dehydrogenase, which is involved in glycerol and G3P metabolism. G3P accumulates in the glpD mutant and represses lsr transcription by preventing cyclic AMP (cAMP)-catabolite activator protein (CAP)-dependent activation. Dihydroxyacetone phosphate (DHAP) also accumulates in the glpD mutant, and DHAP represses lsr transcription by a cAMP-CAP-independent mechanism involving LsrR, the lsr operon repressor. The requirement for cAMP-CAP in lsr activation explains why AI-2 persists in culture fluids of bacteria grown in media containing sugars that cause catabolite repression. These findings show that, depending on the prevailing growth conditions, the amount of time that the AI-2 signal is present and, in turn, the time that a given community of bacteria remains exposed to this signal can vary greatly.

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41

Taga, Michiko E., Julia L. Semmelhack e Bonnie L. Bassler. "The LuxS-dependent autoinducer AI-2 controls the expression of an ABC transporter that functions in AI-2 uptake in Salmonella typhimurium". Molecular Microbiology 42, n. 3 (7 luglio 2008): 777–93. http://dx.doi.org/10.1046/j.1365-2958.2001.02669.x.

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42

Beeston, Anne L., e Michael G. Surette. "pfs-Dependent Regulation of Autoinducer 2 Production in Salmonella enterica Serovar Typhimurium". Journal of Bacteriology 184, n. 13 (1 luglio 2002): 3450–56. http://dx.doi.org/10.1128/jb.184.13.3450-3456.2002.

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Abstract (sommario):

ABSTRACT Bacterial intercellular communication provides a mechanism for signal-dependent regulation of gene expression to promote coordinated population behavior. Salmonella enterica serovar Typhimurium produces a non-homoserine lactone autoinducer in exponential phase as detected by a Vibrio harveyi reporter assay for autoinducer 2 (AI-2) (M. G. Surette and B. L. Bassler, Proc. Natl. Acad. Sci. USA 95:7046-7050, 1998). The luxS gene product mediates the production of AI-2 (M. G. Surette, M. B. Miller, and B. L. Bassler, Proc. Natl. Acad. Sci. USA 96:1639-1644, 1999). Environmental cues such as rapid growth, the presence of preferred carbon sources, low pH, and/or high osmolarity were found to influence the production of AI-2 (M. G. Surette and B. L. Bassler, Mol. Microbiol. 31:585-595, 1999). In addition to LuxS, the pfs gene product (Pfs) is required for AI-2 production, as well as S-adenosylhomocysteine (SAH) (S. Schauder, K. Shokat, M. G. Surette, and B. L. Bassler, Mol. Microbiol. 41:463-476, 2001). In bacterial cells, Pfs exhibits both 5′-methylthioadenosine (MTA) and SAH nucleosidase functions. Pfs is involved in methionine metabolism, regulating intracellular MTA and SAH levels (elevated levels of MTA and SAH are potent inhibitors of polyamine synthetases and S-adenosylmethionine dependent methyltransferase reactions, respectively). To further investigate regulation of AI-2 production in Salmonella, we constructed pfs and luxS promoter fusions to a luxCDABE reporter in a low-copy-number vector, allowing an examination of transcription of the genes in the pathway for signal synthesis. Here we report that luxS expression is constitutive but that the transcription of pfs is tightly correlated to AI-2 production in Salmonella serovar Typhimurium 14028. Neither luxS nor pfs expression appears to be regulated by AI-2. These results suggest that AI-2 production is regulated at the level of LuxS substrate availability and not at the level of luxS expression. Our results indicate that AI-2-dependent signaling is a reflection of metabolic state of the cell and not cell density.

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Andriani, Dwi, e Agni Febrina Pargaputri. "The effects of Acanthus ilicifolius chloroform extract on TLR-2 expression of macrophages in oral candidiasis". Dental Journal (Majalah Kedokteran Gigi) 51, n. 4 (31 dicembre 2018): 205. http://dx.doi.org/10.20473/j.djmkg.v51.i4.p205-209.

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Abstract (sommario):

Background: Immunosuppressed conditions due to long-term corticosteroid and tetracycline consumption are susceptible to fungal invasion, especially by Candida albicans (C. albicans), that requires treatment of oral candidiasis. Toll like receptor-2 (TLR-2) plays a role in candida recognition. Nystatin is regularly employed for oral candidiasis, but produces certain side-effects. Chloroform extract of Acanthus ilicifolius (A. ilicifolius) leaves represents both a potent inhibitor of C. albicans growth and an antioxidant. Purpose: This study aimed to compare the effect of A. ilicifolius leaf chloroform extract and nystatin treatment on TLR-2 expression in oral candidiasis immunosupressed models. Methods: This study constitutes a true experimental investigation incorporating a post test-only control group design. 20 healthy male Rattus novergicus (Wistar), aged 12 weeks and with an average weight of 250g, were immunosuppressed through oral administration of dexamethasoneand tetracycline for a period of 21 days before being induced with C. albicans (ATCC-10231) 6 x 108 for two weeks. The subjects were divided into five groups (n=4/group): healthy (H), no-treatment(P), nystatin treatment(N), A. Ilicifollius (8%) treatment (AI-1) and A. ilicifollius (16%) treatment (AI-2). The subjects were treated for 14 days, with their tongue being subsequently biopsied. TLR-2 expression was subjected to immunohistochemical examination, observed under a microscope (400x magnification) and statistically analyzed (one-way Anova, LSD-test, p<0.05). Results: TLR-2 expression of P (6.25 ± 2.5), N (11.25 ± 0.96), AI-1 (13.00 ± 1.15), AI-2 (12.75 ± 1.7) was higher than H (1.75 ± 0.5). Significant differences existed between N to P, N, AI-1, AI-2; P to N, AI-1 and AI-2 (p<0.05). No significant differences were present between N, AI-1 and AI-2 (p < 0.05). Conclusion: A. ilicifolius extract can increase expression of TLR-2 in oral Candidiasis-immunosuppressed models. A. ilicifolius extract produces the same effect in increasing TLR-2 expression when compared to nystatin.

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Sztajer, Helena, André Lemme, Ramiro Vilchez, Stefan Schulz, Robert Geffers, Cindy Ying Yin Yip, Celine M. Levesque, Dennis G. Cvitkovitch e Irene Wagner-Döbler. "Autoinducer-2-Regulated Genes in Streptococcus mutans UA159 and Global Metabolic Effect of the luxS Mutation". Journal of Bacteriology 190, n. 1 (2 novembre 2007): 401–15. http://dx.doi.org/10.1128/jb.01086-07.

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ABSTRACT Autoinducer 2 (AI-2) is the only species-nonspecific autoinducer known in bacteria and is produced by both gram-negative and gram-positive organisms. Consequently, it is proposed to function as a universal quorum-sensing signal for interaction between bacterial species. AI-2 is produced as the by-product of a metabolic transformation carried out by the LuxS enzyme. To separate the metabolic function of the LuxS enzyme from the signaling role of AI-2, we carried out a global transcriptome analysis of a luxS null mutant culture of Streptococcus mutans UA159, an important cariogenic bacterium and a crucial component of the dental plaque biofilm community, in comparison to a luxS null mutant culture supplemented with chemically pure 4,5-dihydroxy-2,3-pentanedione, the precursor of AI-2. The data revealed fundamental changes in gene expression affecting 585 genes (30% of the genome) which could not be restored by the signal molecule AI-2 and are therefore not caused by quorum sensing but by lack of the transformation carried out by the LuxS enzyme in the activated methyl cycle. All functional classes of enzymes were affected, including genes known to be important for biofilm formation, bacteriocin synthesis, competence, and acid tolerance. At the same time, 59 genes were identified whose transcription clearly responded to the addition of AI-2. Some of them were related to protein synthesis, stress, and cell division. Three membrane transport proteins were upregulated which are not related to any of the known AI-2 transporters. Three transcription factors were identified whose transcription was stimulated repeatedly by AI-2 addition during growth. Finally, a global regulatory protein, the δ subunit of the RNA polymerase (rpoE), was induced 147-fold by AI-2, representing the largest differential gene expression observed. The data show that many phenotypes related to the luxS mutation cannot be ascribed to quorum sensing and have identified for the first time regulatory proteins potentially mediating AI-2-based signaling in gram-positive bacteria.

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Walters, Matthew, Marcelo P. Sircili e Vanessa Sperandio. "AI-3 Synthesis Is Not Dependent on luxS in Escherichia coli". Journal of Bacteriology 188, n. 16 (15 agosto 2006): 5668–81. http://dx.doi.org/10.1128/jb.00648-06.

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Abstract (sommario):

ABSTRACT The quorum-sensing (QS) signal autoinducer-2 (AI-2) has been proposed to promote interspecies signaling in a broad range of bacterial species. AI-2 is spontaneously derived from 4,5-dihydroxy-2,3-pentanedione that, along with homocysteine, is produced by cleavage of S-adenosylhomocysteine (SAH) and S-ribosylhomocysteine by the Pfs and LuxS enzymes. Numerous phenotypes have been attributed to AI-2 QS signaling using luxS mutants. We have previously reported that the luxS mutation also affects the synthesis of the AI-3 autoinducer that activates enterohemorrhagic Escherichia coli virulence genes. Here we show that several species of bacteria synthesize AI-3, suggesting a possible role in interspecies bacterial communication. The luxS mutation leaves the cell with only one pathway, involving oxaloacetate and l-glutamate, for de novo synthesis of homocysteine. The exclusive use of this pathway for homocysteine production appears to alter metabolism in the luxS mutant, leading to decreased levels of AI-3. The addition of aspartate and expression of an aromatic amino acid transporter, as well as a tyrosine-specific transporter, restored AI-3-dependent phenotypes in an luxS mutant. The defect in AI-3 production, but not in AI-2 production, in the luxS mutant was restored by expressing the Pseudomonas aeruginosa S-adenosylhomocysteine hydrolase that synthesizes homocysteine directly from SAH. Furthermore, phenotype microarrays revealed that the luxS mutation caused numerous metabolic deficiencies, while AI-3 signaling had little effect on metabolism. This study examines how AI-3 production is affected by the luxS mutation and explores the roles of the LuxS/AI-2 system in metabolism and QS.

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46

Cluzel, Marie-Eve, Isabelle Zanella-Cléon, Alain J. Cozzone, Klaus Fütterer, Bertrand Duclos e Virginie Molle. "The Staphylococcus aureus Autoinducer-2 Synthase LuxS Is Regulated by Ser/Thr Phosphorylation". Journal of Bacteriology 192, n. 23 (24 settembre 2010): 6295–301. http://dx.doi.org/10.1128/jb.00853-10.

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ABSTRACT The Staphylococcus aureus autoinducer-2 (AI-2) producer protein LuxS is phosphorylated by the Ser/Thr kinase Stk1 at a unique position, Thr14. The enzymatic activity of the phosphorylated isoform of LuxS was abrogated compared to that of nonphosphorylated LuxS, thus providing the first evidence of an AI-2-producing enzyme regulated by phosphorylation and demonstrating that S. aureus possesses an original and specific system for controlling AI-2 synthesis.

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47

Jones, Marcus B., e Martin J. Blaser. "Detection of a luxS-Signaling Molecule in Bacillus anthracis". Infection and Immunity 71, n. 7 (luglio 2003): 3914–19. http://dx.doi.org/10.1128/iai.71.7.3914-3919.2003.

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ABSTRACT Quorum-sensing regulation of density-dependent genes has been described for numerous bacterial species. The partially annotated genome sequence of Bacillus anthracis contains an open reading frame (BA5047) predicted to encode an ortholog of luxS, required for synthesis of the quorum-sensing signaling molecule autoinducer-2 (AI-2). To determine whether B. anthracis produces AI-2, the Vibrio harveyi luminescence bioassay was used. Cell-free conditioned media from vaccine (Sterne) strain 34F2 induced luminescence in V. harveyi reporter strain BB170, indicating its production of AI-2. Cloned BA5047, expressed in Escherichia coli DH5α cells, restored AI-2 activity to these cells. To evaluate whether BA5047 is essential for AI-2 synthesis, it was deleted through allelic exchange with marker rescue; the resulting mutant had no functional luxS activity and had reduced growth in vitro. In the wild-type strain, AI-2 activity was greatest during the exponential phase of growth. In total, these data indicate that BA5047 is a functional luxS ortholog in B. anthracis necessary for growth-phase-specific AI-2 expression. Thus, B. anthracis may utilize extracellular signaling molecules to regulate density-dependent gene expression.

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48

Blehert, David S., Robert J. Palmer, Joao B. Xavier, Jonas S. Almeida e Paul E. Kolenbrander. "Autoinducer 2 Production by Streptococcusgordonii DL1 and the Biofilm Phenotype of a luxS Mutant Are Influenced by Nutritional Conditions". Journal of Bacteriology 185, n. 16 (15 agosto 2003): 4851–60. http://dx.doi.org/10.1128/jb.185.16.4851-4860.2003.

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ABSTRACT The luxS gene, present in many bacterial genera, encodes the autoinducer 2 (AI-2) synthase. AI-2 has been implicated in bacterial signaling, and this study investigated its role in biofilm formation by Streptococcus gordonii, an organism that colonizes human tooth enamel within the first few hours after professional cleaning. Northern blotting and primer extension analyses revealed that S. gordonii luxS is monocistronic. AI-2 production was dependent on nutritional conditions, and maximum AI-2 induction was detected when S. gordonii was grown in the presence of serum and carbonate. In planktonic cultures, AI-2 production rose sharply during the transition from exponential to stationary phase, and the AI-2 concentration peaked approximately 4 h into stationary phase. An S. gordonii luxS mutant that did not produce AI-2 was constructed by homologous recombination. Complementation of the mutant by insertion of an intact luxS gene into the chromosome in tandem with the disrupted gene restored AI-2 production to a level similar to that of the wild-type strain. In planktonic culture, no growth differences were observed between the mutant and wild-type strains when five different media were used. However, when grown for 4 h as biofilms in 25% human saliva under flow, the luxS mutant formed tall microcolonies that differed from those formed by the wild-type and complemented mutant strains. Biofilms of the luxS mutant exhibited finger-like projections of cells that extended into the flow cell lumen. Thus, the inability to produce AI-2 is associated with altered microcolony architecture within S. gordonii biofilms formed in saliva during a time frame consistent with initial colonization of freshly cleaned enamel surfaces.

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Lombardía, Esteban, Adrián J. Rovetto, Ana L. Arabolaza e Roberto R. Grau. "A LuxS-Dependent Cell-to-Cell Language Regulates Social Behavior and Development in Bacillus subtilis". Journal of Bacteriology 188, n. 12 (15 giugno 2006): 4442–52. http://dx.doi.org/10.1128/jb.00165-06.

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Abstract (sommario):

ABSTRACT Cell-to-cell communication in bacteria is mediated by quorum-sensing systems (QSS) that produce chemical signal molecules called autoinducers (AI). In particular, LuxS/AI-2-dependent QSS has been proposed to act as a universal lexicon that mediates intra- and interspecific bacterial behavior. Here we report that the model organism Bacillus subtilis operates a luxS-dependent QSS that regulates its morphogenesis and social behavior. We demonstrated that B. subtilis luxS is a growth-phase-regulated gene that produces active AI-2 able to mediate the interspecific activation of light production in Vibrio harveyi. We demonstrated that in B. subtilis, luxS expression was under the control of a novel AI-2-dependent negative regulatory feedback loop that indicated an important role for AI-2 as a signaling molecule. Even though luxS did not affect spore development, AI-2 production was negatively regulated by the master regulatory proteins of pluricellular behavior, SinR and Spo0A. Interestingly, wild B. subtilis cells, from the undomesticated and probiotic B. subtilis natto strain, required the LuxS-dependent QSS to form robust and differentiated biofilms and also to swarm on solid surfaces. Furthermore, LuxS activity was required for the formation of sophisticated aerial colonies that behaved as giant fruiting bodies where AI-2 production and spore morphogenesis were spatially regulated at different sites of the developing colony. We proposed that LuxS/AI-2 constitutes a novel form of quorum-sensing regulation where AI-2 behaves as a morphogen-like molecule that coordinates the social and pluricellular behavior of B. subtilis.

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Dodge, Jonathan, Roli Khanna, Jed Irvine, Kin-ho Lam, Theresa Mai, Zhengxian Lin, Nicholas Kiddle et al. "After-Action Review for AI (AAR/AI)". ACM Transactions on Interactive Intelligent Systems 11, n. 3-4 (31 dicembre 2021): 1–35. http://dx.doi.org/10.1145/3453173.

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Explainable AI is growing in importance as AI pervades modern society, but few have studied how explainable AI can directly support people trying to assess an AI agent. Without a rigorous process, people may approach assessment in ad hoc ways—leading to the possibility of wide variations in assessment of the same agent due only to variations in their processes. AAR, or After-Action Review, is a method some military organizations use to assess human agents, and it has been validated in many domains. Drawing upon this strategy, we derived an After-Action Review for AI (AAR/AI), to organize ways people assess reinforcement learning agents in a sequential decision-making environment. We then investigated what AAR/AI brought to human assessors in two qualitative studies. The first investigated AAR/AI to gather formative information, and the second built upon the results, and also varied the type of explanation (model-free vs. model-based) used in the AAR/AI process. Among the results were the following: (1) participants reporting that AAR/AI helped to organize their thoughts and think logically about the agent, (2) AAR/AI encouraged participants to reason about the agent from a wide range of perspectives , and (3) participants were able to leverage AAR/AI with the model-based explanations to falsify the agent’s predictions.

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