Academic literature on the topic 'Multi-organisms interactions'

Prey-predator interactions play a pivotal role in elucidating the evolution and adaptation of various organism’s traits. Numerous approaches have been employed to study the dynamics of prey-predator interaction systems, with agent-based methodologies gaining popularity. However, existing agent-based models are limited in their ability to handle multi-modal interactions, which are believed to be crucial for understanding living organisms. Conversely, prevailing prey-predator integration studies often rely on mathematical models and computer simulations, neglecting real-world constraints and noise. These elusive attributes, challenging to model, can lead to emergent behaviors and embodied intelligence. To bridge these gaps, our study designs and implements a prey-predator interaction scenario that incorporates visual and olfactory sensory cues not only in computer simulations but also in a real multi-robot system. Observed emergent spatial-temporal dynamics demonstrate successful transitioning of investigating prey-predator interactions from virtual simulations to the tangible world. It highlights the potential of multi-robotics approaches for studying prey-predator interactions and lays the groundwork for future investigations involving multi-modal sensory processing while considering real-world constraints.

Reproduction is one of the requirements for evolution and a defining feature of life. Yet, across the tree of life, organisms reproduce in many different ways. Groups of cells (e.g., multicellular organisms, colonial microbes, or multispecies biofilms) divide by releasing propagules that can be single-celled or multicellular. What conditions determine the number and size of reproductive propagules? In multicellular organisms, existing theory suggests that single-cell propagules prevent the accumulation of deleterious mutations (e.g., cheaters). However, groups of cells, such as biofilms, sometimes contain multiple metabolically interdependent species. This creates a reproductive dilemma: small daughter groups, which prevent the accumulation of cheaters, are also unlikely to contain the species diversity that is required for ecological success. Here, we developed an individual-based, multilevel selection model to investigate how such multi-species groups can resolve this dilemma. By tracking the dynamics of groups of cells that reproduce by fragmenting into smaller groups, we identified fragmentation modes that can maintain cooperative interactions. We systematically varied the fragmentation mode and calculated the maximum mutation rate that communities can withstand before being driven to extinction by the accumulation of cheaters. We find that for groups consisting of a single species, the optimal fragmentation mode consists of releasing single-cell propagules. For multi-species groups we find various optimal strategies. With migration between groups, single-cell propagules are favored. Without migration, larger propagules sizes are optimal; in this case, group-size dependent fissioning rates can prevent the accumulation of cheaters. Our work shows that multi-species groups can evolve reproductive strategies that allow them to maintain cooperative interactions.

One of the most striking facts about parasites and microbial pathogens that has emerged in the fields of social evolution and disease ecology in the past few decades is that these simple organisms have complex social lives, indulging in a variety of cooperative, communicative and coordinated behaviours. These organisms have provided elegant experimental tests of the importance of relatedness, kin discrimination, cooperation and competition, in driving the evolution of social strategies. Here, we briefly review the social behaviours of parasites and microbial pathogens, including their contributions to virulence, and outline how inclusive fitness theory has helped to explain their evolution. We then take a mechanistically inspired ‘bottom-up’ approach, discussing how key aspects of the ways in which parasites and pathogens exploit hosts, namely public goods, mobile elements, phenotypic plasticity, spatial structure and multi-species interactions, contribute to the emergent properties of virulence and transmission. We argue that unravelling the complexities of within-host ecology is interesting in its own right, and also needs to be better incorporated into theoretical evolution studies if social behaviours are to be understood and used to control the spread and severity of infectious diseases.

Biological clocks are genetically encoded oscillators that allow organisms to keep track of their environment. Among them, the circadian system is a highly conserved timing structure that regulates several physiological, metabolic and behavioural functions with periods close to 24 h. Time is also crucial for everyday activities that involve conscious time estimation. Timing behaviour in the second-to-minutes range, known as interval timing, involves the interaction of cortico-striatal circuits. In this review, we summarize current findings on the neurobiological basis of the circadian system, both at the genetic and behavioural level, and also focus on its interactions with interval timing and seasonal rhythms, in order to construct a multi-level biological clock.

Ecological systems contain a huge amount of quantitative variation between and within species and locations, which makes it difficult to obtain unambiguous verification of theoretical predictions. Ordinary experiments consider just a few explanatory factors and are prone to providing oversimplified answers because they ignore the complexity of the factors that underlie variation. We used multi-objective optimization (MO) for a mechanistic analysis of the potential ecological and evolutionary causes and consequences of variation in the life-history traits of a species of moth. Optimal life-history solutions were sought for environmental conditions where different life stages of the moth were subject to predation and other known fitness-reducing factors in a manner that was dependent on the duration of these life stages and on variable mortality rates. We found that multi-objective optimal solutions to these conditions that the moths regularly experience explained most of the life-history variation within this species. Our results demonstrate that variation can have a causal interpretation even for organisms under steady conditions. The results suggest that weather and species interactions can act as underlying causes of variation, and MO acts as a corresponding adaptive mechanism that maintains variation in the traits of organisms.

Horizontal gene transfer by conjugative plasmids plays a critical role in the evolution of antibiotic resistance. Interactions between bacteria and other organisms can affect the persistence and spread of conjugative plasmids. Here we show that protozoan predation increased the persistence and spread of the antibiotic resistance plasmid RP4 in populations of the opportunist bacterial pathogen Serratia marcescens . A conjugation-defective mutant plasmid was unable to survive under predation, suggesting that conjugative transfer is required for plasmid persistence under the realistic condition of predation. These results indicate that multi-trophic interactions can affect the maintenance of conjugative plasmids with implications for bacterial evolution and the spread of antibiotic resistance genes.

Symbiotic organisms search (SOS) is a promising metaheuristic algorithm that has been studied recently by numerous researchers due to its capability to solve various hard and complex optimization problems. SOS is a powerful optimization technique that mimics the simulation of the typical symbiotic interactions among organisms in an ecosystem. This study presents a new SOS-based hybrid algorithm for solving the challenging construction site layout planning (CSLP) discrete problems. A new algorithm called the hybrid symbiotic organisms search with local operators (HSOS-LO) represents a combination of the canonical SOS and several local search mechanisms aimed at increasing the searching capability in discrete-based solution space. In this study, three CSLP problems that consist of single and multi-floor facility layout problems are tested, and the obtained results were compared with other widely used metaheuristic algorithms. The results indicate the robust performance of the HSOS-LO algorithm in handling discrete-based CSLP problems.

The ability of aquatic organisms to sense the surrounding environment chemically and interpret such signals correctly is crucial for their ecological niche and survival. Although it is an oversimplification of the ecological interactions, we could consider that a significant part of the decisions taken by organisms are, to some extent, chemically driven. Accordingly, chemical contamination might interfere in the way organisms behave and interact with the environment. Just as any environmental factor, contamination can make a habitat less attractive or even unsuitable to accommodate life, conditioning to some degree the decision of organisms to stay in, or move from, an ecosystem. If we consider that contamination is not always spatially homogeneous and that many organisms can avoid it, the ability of contaminants to repel organisms should also be of concern. Thus, in this critical review, we have discussed the dual role of contamination: toxicity (disruption of the physiological and behavioral homeostasis) vs. repellency (contamination-driven changes in spatial distribution/habitat selection). The discussion is centered on methodologies (forced exposure against non-forced multi-compartmented exposure systems) and conceptual improvements (individual stress due to the toxic effects caused by a continuous exposure against contamination-driven spatial distribution). Finally, we propose an approach in which Stress and Landscape Ecology could be integrated with each other to improve our understanding of the threat contaminants represent to aquatic ecosystems.

The present paper addresses the tensions between internalist and radical-interactionist approaches to cognitive neuroscience, and the conflicting conclusions these positions lead to as regards the issue of whether archaeological artefacts constitute ‘results’ or ‘components’ of cognition. Wild systems theory (WST) and the notion of wild agency are presented as a potential resolution. Specifically, WST conceptualizes organisms (i.e. wild agents) as open, multi-scale self-sustaining systems. It is thus able to address the causal properties of wild systems in a manner that is consistent with radical-interactionist concerns regarding multi-scale contingent interactions. Furthermore, by conceptualizing wild agents as self-sustaining embodiments of the persistent, multi-scale contexts that afforded their emergence and in which they sustain themselves, WST is able to address the semantic properties of wild agents in a way that acknowledges the internalist concerns regarding meaningful (i.e. semantic) internal states (i.e. causal content ). In conclusion, WST agrees with radical interactionism and asserts that archaeological artefacts constitute components of cognition. In addition, given its ability to resolve tensions between the internalist and the radical interactionist approaches to cognition, WST is presented as potentially integrative for cognitive science in general.

Evidence shows that diversity and spatial distributions of biological communities are largely driven by the race of living organisms in their adaptation to chemicals synthesized by their neighbors. In this report, the emergence of mathematical models on pure spatial self-organization induced by biochemical suppression (allelopathy) and competition between species were investigated through numerical analysis. For both random and patched initial spatial distributions of species, we demonstrate that warfare survivors are self-organized on the landscape in Turing-like patterns driven by diffusive instabilities of allelochemicals. These patterns are simple; either all species coexist at low diffusion rates or are massively extinct, except for a few at high diffusivities, but they are complex and biodiversity-sustained at intermediate diffusion rates. “Defensive alliances” and ecotones seem to be basic mechanisms that sustain great biodiversity in our hybrid cellular automata model. Moreover, species coexistence and extinction exhibit multi-stationarity.

La formation de biofilm multi-organismes est rarement étudiée en particulier avec des organismes marins. Ce travail a d’abord mis en évidence une hétérogénéité des capacités de formation du biofilm et de la matrice de bactéries isolées de Méditerranée. L’étude de biofilms multi-espèces a permis de révéler des effets antagonistes et bénéfiques de certaines souches sur le développement du biofilm de leurs partenaires. Les interactions entre amibes et bactéries marines inoculées à un faible ratio ont ensuite montré que toutes les souches testées ont été phagocytées par Acanthamoeba castellanii. Cependant, différents mécanismes d’échappement à leur prédateur ont été mis en évidence tels qu’une localisation intranucléolaire des bactéries ou au sein de pelotes fécales expulsées de l’amibe. En revanche, lorsque les amibes ont été ajoutées sur des biofilms monospécifiques ou multi-spécifiques préalablement formés, une majorité de bactéries a fini par se détacher. Le surnageant amibien a également induit un détachement chez deux des bactéries de leur biofilm monospécifique, ainsi que des modifications phénotypiques chez ces mêmes souches, suggérant que des composés amibiens sont secrétés et détectés par les bactéries. Par conséquent, alors qu’on aurait pu s’attendre à un simple broutage des bactéries marines par les amibes, une diversité de comportements bactériens a été mis en évidence donnant une idée sur la diversité des mécanismes d’interaction pouvant exister dans l’environnement marin
The formation of multi-organisms biofilms is poorly studied especially with marine organisms. This work first showed that strains harvested in biofilms from the Mediterranean Sea displayed a heterogeneity in their biofilm formation abilities and a diversity of matrix compounds. The study of multi-species biofilms revealed antagonistic and beneficial effects of some strains on the biofilm development of their partners. The interactions between amoebae and marine bacteria inoculated at a low ratio showed that all the strains tested were phagocytosed by Acanthamoeba castellanii. However, different mechanisms of escapement from their predators have been unraveled, such as a bacterial localization within the cell nucleolus or within fecal pellets expelled from amoebae. However, when the amoebae were added to a preformed bacterial monospecies or multispecies biofilms, a majority of bacteria detached from the surface. The amoebae supernatant induced also a bacterial detachment on two of the bacteria in monospecies biofilms, as well as morphological changes of these bacteria, suggesting that amoeba chemical cues are secreted and detected by the bacteria. Therefore, although a simple grazing of non-pathogenic marine bacteria by amoebae could have been expected, a diversity of bacterial behaviors was unraveled giving an idea on the diversity of interaction mechanisms that may exist in the marine environment

Tomato (Solanum lycopersicum L.) produces an array of volatile secondary metabolites that act as constitutive and induced defenses against a variety of insect pests and diseases. We studied the effect of beneficial microorganisms, an arbuscular mycorrhiza fungus (AM), Glomus intraradices, an entomopathogenic fungus (Bb), Beauveria bassiana and a combination of both (AM+Bb), as well as, pests, such as rootknot nematode (RKN) (Meloidogyne incognita) and beet armyworm (BAW) (Spodoptera exiguae H.) on the production of volatile compounds in the leaves and roots of tomato. Benzyl alcohol, 3-hexenoic acid, total other compounds and β-myrcene were significantly increased (P<0.05) in the leaves by AM and Bb colonization. Upon herbivory, control plants showed a trend for high volatile contents among all four treatment groups contrary to the trend observed without herbivory, when control showed low volatile contents. Herbivory significantly decreased all the volatiles in the leaves compared to those without herbivory. Pest bioassay revealed that these two fungi together can significantly induce resistance against BAW. In the experiment with RKN, a trend was observed with low production of most volatile compounds in the leaves from the RKN plants. Varying durations of herbivory exposure had significant effects on many leaf volatile compounds compared to those without herbivory. Effect of RKN was significant (P<0.05) on the production of methyl salicylate, and (Z)-geraniol in the roots. Interaction effect of RKN with 18 hours of herbivory was significant for (Z)-geraniol, and with 42 hours of herbivory, it was significant for (Z)-geraniol, benzyl alcohol, and total volatiles in the roots. Beet armyworm preferred RKN plants and caused greater damage to them compared to the control plants. Semi-quantitative RT-PCR showed higher expression of the SlSAMT gene in the roots colonized with RKN, compared to the control roots and those from a resistant line. The experiments demonstrated that interaction with these organisms can change the volatile compounds in the leaves and roots of tomato plant, can alter herbivore preference, and can upregulate defense genes such as SlSAMT.

AbstractTriclosan (TCA) is an antibacterial and antimicrobial compound that is incorporated into toothpaste, soap, and liquid dishwasher. Continuous TCA exposure may contribute to the emergence of antibiotic-resistant bacteria in the microbiome. Triclosan also reacts to form dioxins, which bioaccumulate and are toxic to aquatic organisms, impedes the thyroid hormone metabolism of the human body. Laccases are multi copper-containing enzymes that can degrade the aromatic compounds and thus reduce their toxicity. To effectively degrade the compound, it is essential to understand the molecular function of the enzyme. Hence, a molecular docking study of laccase enzymes with Triclosan was done. The Tramates versicolor laccase structure was retrieved from PDB and ligand structure was taken from Pubchem. The binding mode and interaction of TCA and laccase were studied using Auto dock Vina software and the stability of the docked complex had been explored via Molecular Dynamics (MD) simulation study using Schrodinger Desmonde. The binding affinity score was found to be −6.5kcal/mol. The majority of the residues in RMSF were within the 2.5Å limit. The radius of gyration remained within the range from 21.7 to 22.1Å for Laccase – TCA complex throughout the 50 ns simulation. MD simulation results show that the enzyme complex remains stable all through the catalytic action.

Abstract There was a time when the biology of the extracellular matrix was considered quite separately from study of signaling or morphogenesis. This was even reMected in the terminology of the 2eld, where “ground substance” was used to refer to the extracellular matrix. “Ground substance” certainly does not evoke images of dynamic pro- cesses that involve interactions between cells and their environment. We now know that it is impossible to understand the biology of multi- cellular organisms without appreciating that cells create the extracellular matrix that surrounds them and that the matrix reciprocally affects virtually all aspects of cellular behavior.

In their native states, most natural samples exist as complex heterogeneous mixtures, with conformation, associations between phases, and transfer across phases being critical to biological function and environmental reactivity. Often analytical techniques to observe natural samples tend to be destructive to the sample itself and/or can only monitor individual phases (solution or solid). Comprehensive multiphase NMR (CMP-NMR) is a non-invasive technique capable of monitoring all phases (solution, gel, and solid) and their interactions such as binding and phase transformation in intact samples at the molecular level. Thus far, CMP-NMR has been used to observe numerous environmental multi-phase processes in soil, as well as living organisms. This chapter will discuss all applications of CMP-NMR to date to demonstrate the applicability and versatility of CMP-NMR to observe structural changes and interactions in complex systems.

The emergence of biogenic nanomaterials as novel antimicrobials introduces a new paradigm in human health care. Based on the recent reports of the World Health Organization, infectious diseases pose one of the greatest health challenges. Increased multi-drug resistance prevalence among human pathogens, due to the inefficiency of commercially available antimicrobial drugs in the market is a great threat to humans. The poor solubility, stability and side effects of the antibacterial therapy prompted the researchers to explore new innovative strategies for developing new antimicrobials. Recently, biogenic nanoparticles have proven their effectiveness against multidrug-resistant (MDR) pathogens as an alternative to conventional antibiotics. Biogenic nanoparticles such as silver nanoparticles (AgNPs) and Zinc Oxide nanoparticles (ZnONPs) are easy to produce, biocompatible, provide enhanced uptake and are eco-friendly. Moreover, the capping of the biogenic nanocrystals provides an active surface for interaction with biological components, facilitated by free active surface functional groups to enhance their efficacy and delivery. Inorganic nanocrystals (AgNPs and ZnONPs) are effective both as nano-bactericides and as nanocarriers against sensitive and MDR) pathogens. The present chapter focuses on the utilization of the recent nanosystems to combat drug resistance in human pathogens. Nanomedicine represents a new generation of potiential antimicrobial candidates capable of combating the drug resistance in various pathogenic organisms.

Molecular modeling has gained increasing importance in recent years for predicting important structural properties of large biomolecular systems such as RNA which play a critical role in various biological processes. Given the complexity of biopolymers and their interactions within living organisms, efficient and adaptive multi-scale modeling approaches are necessary if one is to reasonably perform computational studies of interest. These studies nominally involve multiple important physical phenomena occurring at different spatial and temporal scales. These systems are typically characterized by large number of degrees of freedom O(103) – O(107). The temporal domains range from sub-femto seconds (O(10−16)) associated with the small high frequency oscillations of individual tightly bonded atoms to milliseconds (O(10−3)) or greater for the larger scale conformational motion. The traditional approach for molecular modeling involved fully atomistic models which results in fully decoupled equations of motion. The problems with this approach are well documented in literature.

Alessandro Camiz ¹ ¹ Department of Architecture, Girne American University, Cyprus, Association for Historical Dialogue and Research, Home for Cooperation (H4C), 28 Marcou Dracou Street, Nicosia, Cyprus, 1102. E-mail: alessandrocamiz@gau.edu.tr Keywords (3-5): urban tissues, urban morphology, urban routes, theory, history Conference topics and scale: Tools of analysis in urban morphology Recent urban morphology studies consider urban tissues as living organisms changing in time (Strappa, Carlotti, Camiz, 2016), following this assumption the theory should examine more analytically what Muratori called ‘medievalisation’ (Muratori, 1959), a term describing some of the transformations of urban routes happened in the middle ages. The paper considers the diachronic deformation of routes, and other multi-scalar occurrences of the attraction phenomena (Charalambous, Geddes, 2015), introducing the notion of attractors and repellers. Archaeological studies already do consider attractors and repellers as a tool to interpret some territorial transformations, following the assumption that “the trajectory that a system follows through time is the result of a continuous dynamic interaction between that system and the multiple 'attractors' in its environment” (Renfrew, Bahn, 2013, p. 184). There are different elements that can act as attractors in an urban environment, such as bridges, city walls, city gates, water systems, markets, special buildings, and it is possible to consider each of these anthropic attractors as equivalent to a morphological attractor at the geographical scale. We can even interpret the ridge-top theory (Caniggia, 1976) as the result of attraction and repellence of geographic features on anthropic routes. The territorial scale analysis is the methodological base of the theory, but the attractors herein considered operate at the urban scale, deviating locally across time from a rectilinear trajectory and defining a specific urban fabric. The research interprets and reads the effects of attractors on urban routes and fabrics as a method for the reconstruction of Nicosia’s medieval city walls, in continuity between the Conzenian approach (Whitehand, 2012) and the Italian School of Urban Morphology (Marzot, 2002). References:, Muratori, S. (1959) Studi per un’operante storia urbana di Venezia (Istituto Poligrafico dello Stato, Roma). Caniggia, G. (1976) Strutture dello spazio antropico. Studi e note (Uniedit, Firenze). Marzot, N. (2002) ‘The study of urban form in Italy’, Urban Morphology 6.2, 59-73. Whitehand, J.W.R. (2012) ‘Issues in urban morphology’, Urban Morphology 16.1, 55-65. Renfrew, C., Bahn, P. (eds.) (2013) Archaeology: The Key Concepts, (London, Routledge). Charalambous, N., Geddes, I. (2015) ‘Making Spatial Sense of Historical Social Data’, Journal of Space Syntax 6.1, 81-101. Strappa, G., Carlotti, P., Camiz, A. (2016) Urban Morphology and Historical Fabrics. Contemporary design of small towns in Latium (Gangemi, Roma).

Brucella Mutagenesis (TAMU) The working hypothesis for this study was that survival of Brucella vaccines was directly related to their persistence in the host. This premise is based on previously published work detailing the survival of the currently employed vaccine strains S19 and Rev 1. The approach employed signature-tagged mutagenesis to construct mutants interrupted in individual genes, and the mouse model to identify mutants with attenuated virulence/survival. Intracellular survival in macrophages is the key to both reproductive disease in ruminants and reticuloendothelial disease observed in most other species. Therefore, the mouse model permitted selection of mutants of reduced intracellular survival that would limit their ability to cause reproductive disease in ruminants. Several classes of mutants were expected. Colonization/invasion requires gene products that enhance host-agent interaction or increase resistance to antibacterial activity in macrophages. The establishment of chronic infection requires gene products necessary for intracellular bacterial growth. Maintenance of chronic infection requires gene products that sustain a low-level metabolism during periods characterized little or no growth (1, 2). Of these mutants, the latter group was of greatest interest with regard to our originally stated premise. However, the results obtained do not necessarily support a simplistic model of vaccine efficacy, i.e., long-survival of vaccine strains provides better immunity. Our conclusion can only be that optimal vaccines will only be developed with a thorough understanding of host agent interaction, and will be preferable to the use of fortuitous isolates of unknown genetic background. Each mutant could be distinguished from among a group of mutants by PCR amplification of the signature tag (5). This approach permitted infection of mice with pools of different mutants (including the parental wild-type as a control) and identified 40 mutants with apparently defective survival characteristics that were tentatively assigned to three distinct classes or groups. Group I (n=13) contained organisms that exhibited reduced survival at two weeks post-infection. Organisms in this group were recovered at normal levels by eight weeks and were not studied further, since they may persist in the host. Group II (n=11) contained organisms that were reduced by 2 weeks post infection and remained at reduced levels at eight weeks post-infection. Group III (n=16) contained mutants that were normal at two weeks, but recovered at reduced levels at eight weeks. A subset of these mutants (n= 15) was confirmed to be attenuated in mixed infections (1:1) with the parental wild-type. One of these mutants was eliminated from consideration due to a reduced growth rate in vitro that may account for its apparent growth defect in the mouse model. Although the original plan involved construction of the mutant bank in B. melitensis Rev 1 the low transformability of this strain, prevented accumulation of the necessary number of mutants. In addition, the probability that Rev 1 already carries one genetic defect increases the likelihood that a second defect will severely compromise the survival of this organism. Once key genes have been identified, it is relatively easy to prepare the appropriate genetic constructs (knockouts) lacking these genes in B. melitensis Rev 1 or any other genetic background. The construction of "designer" vaccines is expected to improve immune protection resulting from minor sequence variation corresponding to geographically distinct isolates or to design vaccines for use in specific hosts. A.2 Mouse Model of Brucella Infection (UWISC) Interferon regulatory factor-1-deficient (IRF-1-/- mice have diverse immunodeficient phenotypes that are necessary for conferring proper immune protection to intracellular bacterial infection, such as a 90% reduction of CD8+ T cells, functionally impaired NK cells, as well as a deficiency in iNOS and IL-12p40 induction. Interestingly, IRF-1-/- mice infected with diverse Brucella abortus strains reacted differently in a death and survival manner depending on the dose of injection and the level of virulence. Notably, 50% of IRF-1-/- mice intraperitoneally infected with a sublethal dose in C57BL/6 mice, i.e., 5 x 105 CFU of virulent S2308 or the attenuated vaccine S19, died at 10 and 20 days post-infection, respectively. Interestingly, the same dose of RB51, an attenuated new vaccine strain, did not induce the death of IRF-1-/- mice for the 4 weeks of infection. IRF-1-/- mice infected with four more other genetically manipulated S2308 mutants at 5 x 105 CFU also reacted in a death or survival manner depending on the level of virulence. Splenic CFU from C57BL/6 mice infected with 5 x 105 CFU of S2308, S19, or RB51, as well as four different S2308 mutants supports the finding that reduced virulence correlates with survival Of IRF-1-/- mice. Therefore, these results suggest that IRF-1 regulation of multi-gene transcription plays a crucial role in controlling B. abortus infection, and IRF-1 mice could be used as an animal model to determine the degree of B. abortus virulence by examining death or survival. A3 Diagnostic Tests for Detection of B. melitensis Rev 1 (Kimron) In this project we developed an effective PCR tool that can distinguish between Rev1 field isolates and B. melitensis virulent field strains. This has allowed, for the first time, to monitor epidemiological outbreaks of Rev1 infection in vaccinated flocks and to clearly demonstrate horizontal transfer of the strain from vaccinated ewes to unvaccinated ones. Moreover, two human isolates were characterized as Rev1 isolates implying the risk of use of improperly controlled lots of the vaccine in the national campaign. Since atypical B. melitensis biotype 1 strains have been characterized in Israel, the PCR technique has unequivocally demonstrated that strain Rev1 has not diverted into a virulent mutant. In addition, we could demonstrate that very likely a new prototype biotype 1 strain has evolved in the Middle East compared to the classical strain 16M. All the Israeli field strains have been shown to differ from strain 16M in the PstI digestion profile of the omp2a gene sequence suggesting that the local strains were possibly developed as a separate branch of B. melitensis. Should this be confirmed these data suggest that the Rev1 vaccine may not be an optimal vaccine strain for the Israeli flocks as it shares the same omp2 PstI digestion profile as strain 16M.