Academic literature on the topic 'KdpDE'

Two-component systems (TCSs), which consist of a histidine kinase (HK) sensor and a response regulator (RR), are important for bacteria to quickly sense and respond to various environmental signals. HKs and RRs typically function as a cognate pair, interacting only with one another to transduce signaling. Precise signal transduction in a TCS depends on the specific interactions between the receiver domain (RD) of the RR and the dimerization and histidine phosphorylation domain (DHp) of the HK. Here, we determined the complex structure of KdpDE, a TCS consisting of the HK KdpD and the RR KdpE, which is responsible for K+ homeostasis. Both the RD and the DNA binding domain (DBD) of KdpE interacted with KdpD. Although the RD of KdpE and the DHp of KdpD contributed to binding specificity, the DBD mediated a distinct interaction with the catalytic ATP-binding (CA) domain of KdpD that was indispensable for KdpDE-mediated signal transduction. Moreover, the DBD-CA interface largely overlapped with that of the DBD-DNA complex, leading to competition between KdpD and its target promoter in a KdpE phosphorylation–dependent manner. In addition, the extended C-terminal tail of the CA domain was critical for stabilizing the interaction with KdpDE and for signal transduction. Together, these data provide a molecular basis for specific KdpD and KdpE interactions that play key roles in efficient signal transduction and transcriptional regulation by this TCS.

ABSTRACT Transcription of the K+ transport operonkdp in Escherichia coli is induced during K+-limited growth by the action of a dual-component phosphorelay regulatory system comprised of a sensor kinase (integral membrane protein), KdpD, and a DNA-binding response regulator (cytoplasmic protein), KdpE. In this study, we screened for newdke (named dke for decreased kdpexpression) mutations (in loci other than kdpDE) that led to substantially decreased kdp expression. Onedke mutation was shown to be in hns, encoding the nucleoid protein H-NS. Another dke mutation was mapped to trxB (encoding thioredoxin reductase), and an equivalent reduction in kdp expression was demonstrated also fortrxA mutants that are deficient in thioredoxin 1. Exogenously provided dithiothreitol rescued the kdpexpression defect in trxB but not trxA mutants. Neither trxB nor trxA affected gene regulation mediated by another dual-component system tested, EnvZ-OmpR. Mutations in genes dsbC and dsbD did not affectkdp expression, suggesting that the trx effects on kdp are not mediated by alterations in protein disulfide bond status in the periplasm. Reduced kdp expression was observed even in a trxB strain that harbored a variant KdpD polypeptide bearing no Cys residues. A trxB hns double mutant was even more severely affected for kdp expression than either single mutant. The dke mutations themselves had no effect on strength of the signal controlling kdpexpression, and constitutive mutations in kdpDE were epistatic to hns and trxB. These results indicate that perturbations in cytoplasmic thiol oxidation status and in levels of the H-NS protein exert additive effects, direct or indirect, at a step(s) upstream of KdpD in the signal transduction pathway, which significantly influence the magnitude of KdpD kinase activity obtained for a given strength of the inducing signal forkdp transcription.

ABSTRACT The kdpFABC operon of Escherichia coli, coding for the high-affinity K+ transport system KdpFABC, is transcriptionally regulated by the products of the adjacently located kdpDE genes. The KdpD protein is a membrane-bound sensor kinase consisting of a large N-terminal domain and a C-terminal transmitter domain interconnected by four transmembrane segments (the transmembrane segments together with the C-terminal transmitter domain of KdpD are referred to as CTD), while KdpE is a cytosolic response regulator. We have cloned and sequenced the kdp operon from a nitrogen-fixing, filamentous cyanobacterium, Anabaena sp. strain L-31 (GenBank accession. number AF213466 ). The kdpABC genes are similar in size to those of E. coli, but the kdpD gene is short (coding only for 365 amino acids), showing homology only to the N-terminal domain of E. coli KdpD. A kdpE-like gene is absent in the vicinity of this operon. Anabaena KdpD with six C-terminal histidines was overproduced in E. coli and purified by Ni2+-nitrilotriacetic acid affinity chromatography. With antisera raised against the purified Anabaena KdpD, the protein was detected in Anabaena sp. strain L-31 membranes. The membrane-associated or soluble form of the Anabaena KdpD(6His) could be photoaffinity labeled with the ATP analog 8-azido-ATP, indicating the presence of an ATP binding site. The coproduction of Anabaena KdpD with E. coli KdpD-CTD decreased E. coli kdpFABC expression in response to K+ limitation in vivo relative to the wild-type KdpD-CTD protein. In vitro experiments revealed that the kinase activity of the E. coli KdpD-CTD was unaffected, but its phosphatase activity increased in the presence of Anabaena KdpD(6His). To our knowledge this is the first report where a heterologous N-terminal domain (Anabaena KdpD) is shown to affect in trans KdpD-CTD (E. coli) activity, which is just opposite to that observed for the KdpD-N-terminal domain of E. coli.

ABSTRACTThe Kdp system is widely distributed among bacteria. InEscherichia coli, the Kdp-ATPase is a high-affinity K+uptake system and its expression is activated by the KdpDE two-component system in response to K+limitation or salt stress. However, information about the role of this system in many bacteria still remains obscure. Here we demonstrate that KdpFABC inStaphylococcus aureusis not a major K+transporter and that the main function of KdpDE is not associated with K+transport but that instead it regulates transcription for a series of virulence factors through sensing external K+concentrations, indicating that this bacterium might modulate its infectious status through sensing specific external K+stimuli in different environments. Our results further reveal thatS. aureusKdpDE is upregulated by the Agr/RNAIII system, which suggests that KdpDE may be an important virulence regulator coordinating the external K+sensing and Agr signaling during pathogenesis in this bacterium.

The quorum sensing two-component system (TCS) QseBC has been linked to virulence, motility and metabolism regulation in multiple Gram-negative pathogens, including Enterohaemorrhagic Escherichia coli (EHEC), Uropathogenic E. coli (UPEC) and Salmonella enterica. In EHEC, the sensor histidine kinase (HK) QseC detects the quorum sensing signalling molecule AI-3 and also acts as an adrenergic sensor binding host epinephrine and norepinephrine. Downstream changes in gene expression are mediated by phosphorylation of its cognate response regulator (RR) QseB, and ʻcross-talksʼ with non-cognate regulators KdpE and QseF to activate motility and virulence. In UPEC, cross-talk between QseBC and TCS PmrAB is crucial in the regulation and phosphorylation of QseB RR that acts as a repressor of multiple pathways, including motility. Here, we investigated QseBC regulation of motility in the atypical Enteropathogenic E. coli (EPEC) strain O125ac:H6, causative agent of persistent diarrhoea in children, and its possible cross-talk with the KdpDE and PmrAB TCS. We showed that in EPEC QseB acts as a repressor of genes involved in motility, virulence and stress response, and in absence of QseC HK, QseB is likely activated by the non-cognate PmrB HK, similarly to UPEC. We show that in absence of QseC, phosphorylated QseB activates its own expression, and is responsible for the low motility phenotypes seen in a QseC deletion mutant. Furthermore, we showed that KdpD HK regulates motility in an independent manner to QseBC and through a third unidentified party different to its own response regulator KdpE. We showed that PmrAB has a role in iron adaptation independent to QseBC. Finally, we showed that QseB is the responsible for activation of colistin and polymyxin B resistance genes while PmrA RR acts by preventing QseB activation of these resistance genes.

Soil salinity stress is a detrimental factor in crops production. Conventional methods of soil management and reclamation have been proved useless. On the contrary, exploiting the inherent genes and mechanisms of halotolerant bacteria can bring revolution in agriculture. Present study was designed to characterize ATPase dependent protein complexes kdpFABC and kdpDE in a salt tolerant bacterium Alcaligenes xylosoxydans. This complex enables plants to endure the saline environmental conditions through enhancing the K+ ions influx. For characterization, protein sequences of three isoforms of kdpA, four of kdpB, two of kdpC and one of kdpE were retrieved from Uniprot database. These were analyzed via ProtParam tool, AlphaFold protein database and HDOCK server. Highest affinity for ATP molecule was observed in kdpB confirming its reported function of ATP hydrolysis. All documented proteins were found polar (except kdpE), alkaline (except one isoform of each kdpA and kdpB), thermostable, to exhibit complex 3D structure (except for kdpC and E) and in vitro stability. These properties of subunit proteins can be exploited to engineer the complex and produce osmotolerant transgenic plants

ABSTRACT Autoinducer 2 (AI-2) is widely recognized as a signal molecule for intra- and interspecies communication in Gram-negative bacteria, but its signaling function in Gram-positive bacteria, especially in Staphylococcus aureus, remains obscure. Here we reveal the role of LuxS in the regulation of capsular polysaccharide synthesis in S. aureus NCTC8325 and show that AI-2 can regulate gene expression and is involved in some physiological activities in S. aureus as a signaling molecule. Inactivation of luxS in S. aureus NCTC8325 resulted in higher levels of transcription of capsular polysaccharide synthesis genes. The survival rate of the luxS mutant was higher than that of the wild type in both human blood and U937 macrophages. In comparison to the luxS mutant, a culture supplemented with chemically synthesized 4,5-dihydroxy-2,3-pentanedione (DPD), the AI-2 precursor molecule, restored all the parental phenotypes, suggesting that AI-2 has a signaling function in S. aureus. Furthermore, we demonstrated that the LuxS/AI-2 signaling system regulates capsular polysaccharide production via a two-component system, KdpDE, whose function has not yet been clarified in S. aureus. This regulation occurred via the phosphorylation of KdpE binding to the cap promoter.

Abstract2-keto-3-L-arabinonate dehydratase (L-KdpD) and 2-keto-3-D-xylonate dehydratase (D-KdpD) are the third enzymes in the Weimberg pathway catalyzing the dehydration of respective 2-keto-3-deoxy sugar acids (KDP) to α-ketoglutaric semialdehyde (KGSA). The Weimberg pathway has been explored recently with respect to the synthesis of chemicals from L-arabinose and D-xylose. However, only limited work has been done toward characterizing these two enzymes. In this work, several new L-KdpDs and D-KdpDs were cloned and heterologously expressed in Escherichia coli. Following kinetic characterizations and kinetic stability studies, the L-KdpD from Cupriavidus necator (CnL-KdpD) and D-KdpD from Pseudomonas putida (PpD-KdpD) appeared to be the most promising variants from each enzyme class. Magnesium had no effect on CnL-KdpD, whereas increased activity and stability were observed for PpD-KdpD in the presence of Mg2+. Furthermore, CnL-KdpD was not inhibited in the presence of L-arabinose and L-arabinonate, whereas PpD-KdpD was inhibited with D-xylonate (I50 of 75 mM), but not with D-xylose. Both enzymes were shown to be highly active in the one-step conversions of L-KDP and D-KDP. CnL-KdpD converted > 95% of 500 mM L-KDP to KGSA in the first 2 h while PpD-KdpD converted > 90% of 500 mM D-KDP after 4 h. Both enzymes in combination were able to convert 83% of a racemic mixture of D,L-KDP (500 mM) after 4 h, with both enzymes being specific toward the respective stereoisomer. Key points• L-KdpDs and D-KdpDs are specific toward L- and D-KDP, respectively.• Mg2+affected activity and stabilities of D-KdpDs, but not of L-KdpDs.• CnL-KdpD and PpD-KdpD converted 0.5 M of each KDP isomer reaching 95 and 90% yield.• Both enzymes in combination converted 0.5 M racemic D,L-KDP reaching 83% yield.

ABSTRACTNucleotide signaling molecules are important intracellular messengers that regulate a wide range of biological functions. The human pathogenStaphylococcus aureusproduces the signaling nucleotide cyclic di-AMP (c-di-AMP). This molecule is common among Gram-positive bacteria and in many organisms is essential for survival under standard laboratory growth conditions. In this study, we investigated the interaction of c-di-AMP with theS. aureusKdpD protein. The sensor kinase KdpD forms a two-component signaling system with the response regulator KdpE and regulates the expression of thekdpDEgenes and thekdpFABCoperon coding for the Kdp potassium transporter components. Here we show that theS. aureusKdpD protein binds c-di-AMP specifically and with an affinity in the micromolar range through its universal stress protein (USP) domain. This domain is located within the N-terminal cytoplasmic region of KdpD, and amino acids of a conserved SXS-X20-FTAXY motif are important for this binding. We further show that KdpD2, a second KdpD protein found in someS. aureusstrains, also binds c-di-AMP, and our bioinformatics analysis indicates that a subclass of KdpD proteins in c-di-AMP-producing bacteria has evolved to bind this signaling nucleotide. Finally, we show that c-di-AMP binding to KdpD inhibits the upregulation of thekdpFABCoperon under salt stress, thus indicating that c-di-AMP is a negative regulator of potassium uptake inS. aureus.IMPORTANCEStaphylococcus aureusis an important human pathogen and a major cause of food poisoning in Western countries. A common method for food preservation is the use of salt to drive dehydration. This study sheds light on the regulation of potassium uptake inStaphylococcus aureus, an important aspect of this bacterium's ability to tolerate high levels of salt. We show that the signaling nucleotide c-di-AMP binds to a regulatory component of the Kdp potassium uptake system and that this binding has an inhibitory effect on the expression of thekdpgenes encoding a potassium transporter. c-di-AMP binds to the USP domain of KdpD, thus providing for the first time evidence for the ability of such a domain to bind a cyclic dinucleotide.

La tuberculose (TB) est, hors COVID, la première cause de décès lié à un agent infectieux. La détermination rapide du profil de résistance complet de Mycobacterium tuberculosis (Mtb) est essentielle pour démarrer un traitement adapté dans les cas de TB multirésistante (MDR) et ainsi limiter l’acquisition de résistances supplémentaires, augmenter les chances de succès thérapeutique et réduire la transmission de ces souches. Il existe 9 lignées principales au sein du complexe M. tuberculosis, dont 2 sont largement répandues dans le monde (L2 et L4). Au sein de la lignée 2, le clone W148 (ou complexe clonal CC 100-32) a diffusé récemment en Europe et en Asie. Cette diffusion pourrait s'expliquer par des mutations spécifiques au sein du génome.En premier lieu, nous avons étudié la technologie Deeplex Myc-TB pour détecter rapidement le génotype et la résistance des souches cliniques de Mtb MDR. Cette technologie, basée sur une PCR multiplex et un séquençage haut débit, détermine à la fois l’espèce (hsp65), le génotype (spoligotype) et la résistance à 13 antituberculeux de première et seconde ligne (18 cibles). Le travail d’évaluation a inclus 112 prélèvements et 94 souches adressés au Centre National de Référence des Mycobactéries et de la Résistance des Mycobactéries aux Antituberculeux (CNR MyRMA). Nous avons observé que le test Deeplex Myc-TB fonctionne sur prélèvement positif à l’examen microscopique et sur souche. Les profils de résistance obtenus sont concordants à 85,4% avec les résultats de la méthode phénotypique de référence. L'utilisation de Deeplex Myc-TB fournit des résultats en une dizaine de jours, soit environ 6 semaines avant ceux de l’antibiogramme phénotypique. Deeplex Myc-TB permet donc d’adapter l’antibiothérapie bien avant que ce qui était fait jusqu’à présent, pour le bénéfice des patients. Nous avons ainsi pu valider cet outil maintenant utilisé en routine au CNR MyRMA. Nous avons ensuite étudié les mutations spécifiques du CC 100-32 MDR. L’analyse du génome complet de 36 souches reçues au CNR MyRMA a permis d’identifier 30 mutations non synonymes et petites délétions spécifiques. Parmi elles, nous avons choisi d’étudier celles présentes dans kdpD et whiB6, car des données de la littérature semblent montrer un impact de ces gènes sur la virulence de la souche. KdpDE est un système à deux composants régulant l’expression du système de transport du potassium inductible KdpFABC. La mutation présente dans le complexe CC 100-32 MDR est une délétion de 2 nucléotides à la fin du gène kdpD entraînant une protéine de fusion KdpDE. Nous avons donc construit un tel mutant chez Mtb H37Rv en supprimant les deux gènes kdpD et kdpE avant de le complémenter avec la forme sauvage ou mutée de kdpDE. Nous n’avons pas observé de différence de croissance in vitro des différentes souches, y compris en l’absence de potassium, suggérant que KdpDE n’est pas essentiel pour le fitness de la bactérie en présence et absence de potassium. L’étude de l’impact de la délétion sur l’activité transcriptionnelle et la virulence est en cours. D’autre part, WhiB6 est un facteur de transcription qui régule le système ESX-1, nécessaire à la virulence. Des travaux du laboratoire ont permis d'obtenir le mutant ∆whiB6 et les souches complémentées WT et mutée (T51P) et leur ré-analyse indique que la souche mutée T51P entraîne une production d’ESAT-6 et de cytokines pro-inflammatoires plus faible que la souche sauvage ; nous réalisons actuellement une analyse du transcriptome. Les premiers résultats obtenus semblent indiquer que la mutation T51P dans WhiB6 entraîne moins de virulence et d’inflammation. Ce travail a permis de valider un outil maintenant indispensable au diagnostic des TB MDR en routine au CNR MyRMA et d’étudier la diffusion d’un clone MDR à travers les fonctions de deux facteurs de transcription impliqués dans la virulence
Tuberculosis (TB) is, excluding COVID, the leading cause of death linked to an infectious agent. Rapid determination of the full resistance profile of Mycobacterium tuberculosis (Mtb) is essential to initiate appropriate treatment of multidrug resistant (MDR) cases, thereby limiting the acquisition of additional resistance, increasing the chances of therapeutic success and reducing transmission of these strains. There are 9 main lineages within the M. tuberculosis complex, 2 of which are widespread throughout the world (L2 and L4). Within lineage 2, the clone W148 (or clonal complex CC 100-32) has recently spread to Europe and Asia. This spread could be explained by specific mutations within the genome.First, we investigated the Deeplex Myc-TB tool for rapid detection of genotype and resistance in clinical Mtb MDR strains. The Deeplex Myc-TB technology, based on multiplex PCR and high-throughput sequencing, determines species (hsp65), genotype (spoligotype) and resistance to 13 first- and second-line anti-tuberculosis drugs (18 targets). Our evaluation included 112 samples and 94 strains sent to the Centre National de Référence des Mycobactéries et de la Résistance des Mycobactéries aux Antituberculeux (CNR MyRMA). We have observed that the Deeplex Myc-TB test is efficient on microscopically positive samples and strains. The resistance profiles obtained are 85.4% concordant with the results of the phenotypic reference method. The use of Deeplex Myc-TB provides results within ten days, and around 6 weeks before those of the phenotypic antibiogram. Deeplex Myc-TB can therefore be used to adapt antibiotic therapy much earlier than was previously possible, to the patient benefit. We were thus able to validate this tool, which is now routinely used at CNR MyRMA. We next studied mutations specific to CC 100-32 MDR. Genome-wide analysis of 36 strains received at CNR MyRMA identified 30 non-synonymous mutations and small deletions specific to CC 100-32 MDR strains. Among these, we chose to study mutations present in kdpD and whiB6, as data in the literature indicated an impact of these genes on the virulence of the strain. On the one hand, KdpDE is a two-component system regulating expression of the inducible potassium transport system KdpFABC. The mutation present in the CC 100-32 MDR complex is a 2-nucleotides deletion at the end of the kdpD gene, resulting in a KdpDE fusion protein. We therefore constructed such a mutant in Mtb H37Rv by deleting both the kdpD and kdpE genes before complementing it with the wild-type or mutated form of kdpDE. We observed no difference in the in vitro growth of the different strains, even in the absence of potassium, suggesting that KdpDE is not essential for bacterial fitness in presence or absence of potassium. The impact of the deletion on transcriptional activity and virulence is currently being studied. On the other hand, WhiB6 is a transcription factor that regulates the ESX-1 system, necessary for virulence. Work from the laboratory generated a ∆whiB6 mutant and the complemented WT and mutated (T51P) strains and their re-analysis indicated that T51P mutant strain produces less ESAT-6 and pro-inflammatory cytokines than the wild-type strain. Our transcriptome analysis of these strains is currently underway. Initial results suggest that the T51P mutation in WhiB6 results in less virulence and inflammation. This work has validated a tool that is now essential for routine diagnosis of MDR TB at CNR MyRMA, and to study the spread of an MDR clone through the function of two transcription factors involved in virulence

碩士
國立臺灣大學
醫學檢驗暨生物技術學研究所
107
Proteus mirabilis with the swarming characteristic often causes urinary tract infections occurring mainly in patients with the long-term implantation of urinary catheters. According to previous study, potassium plays an important role in maintaining the function, pathogenicity and toxicity of bacteria. The lack of potassium transporters results in the decrease of secretion proteins and the invasion toward epilethial cells of Salmonella. KdpDE two-component system is a wildly expressed kinase/response regulator in bacteria. Intracellular KdpE is phosphorylated by KdpD when encountering a decreased concentration of potassium, which enhances the expression of KdpFABC potassium transporter. On the other hand, the increased concentration of potassium inhibits KdpE signal then decreased the expression level of KdpFABC to regulate the intracellular concentration of potassium. It has been proven that KdpDE is crucial to the pathogenicity of bacteria such as Yersinia pestis kdpDE mutant is with lower survival than wild type, Salmonella Typhimurium kdpDE mutant leads to a lower infectious rate to nematode and lower survival rate in marcophages as well as in high salinity condition. KdpDE regulates the KdpFABC and influences the uptake of potassium. The aim of this research is to investigate the gene regulation and function of the KdpDE two-component system in uropathogenic Proteus mirabilis. We discovered that kdpFABCDE in N2 genome of P. mirabilis is with 60% similarity with E.coli and S. Typhimurium. The kdpF promoter activity showed the same expression pattern as E.coli and S. Typhimurium in response to the potassium concentration. We proved kdpFABCDE can be a transcriptional unit under low potassium. Subsequently the phenotype of kdpE mutant, wild type, kdpE complementation and kdpE overexpression were analyzed. The tolerance to acid, H2O2 and high salt of the kdpE overexpression strain but not mutant was significantly better than the wild type. We showed kdpF promoter activity was almost no expression in both wild type and mutant in LB, instead of being highly induced in the kdpE overexpression strain. We then identified low K+, high Na+, H202, H+, or glucose as signal to trigger expression of kdpFABC through the kdpDE signal transduction pathway. Under high Na+and low K+ concentration, the salt-resistant, acid-resistant and anti-oxidation ability of wild type are significantly better than of mutant. We also demonstrated un phosphorylated KdpE still can induce kdpF expression in a less extent. Besides, kdpD mutant had no difference with kdpE mutant in terms of the phenotypes and the regulation of kdpFABC operon, suggesting kdpF promoter is solely regulated by kdpDE pathway under the condition used low K+, high Na+ condition. Moreover, overexpression of PtsN inhibited the activity of kdpF promoter and bacterial two-hybrid assay showed interaction between KdpD and PtsN. In summary, KdpDE regulated the expression of kdpFABC no matter KdpE is phosphorylated or not. Low K+, high Na+, high H+, and high H2O2 are signals of the KdpDE two component system. Low K+or high Na+ induces expression downstream gene of the KdpDE system to protect bacteria from the damages of H2O2 stresss, high saltanity and highly acidic condition.

Unter K+-limitierenden Wachstumsbedingungen oder, in wesentlich geringerem Ausmaß, unter Salzstress synthetisiert E. coli den KdpFABC-Komplex, ein hoch-affines K+-Transportsystem (Km ~ 2μM). Die Regulation der Expression des kdpFABC-Operons erfolgt durch das Sensorkinase/Antwortregulator-System KdpD/KdpE. Ziel des ersten Teils dieser Arbeit war die Identifizierung des Stimulus, der von der Sensorkinase KdpD wahrgenommen wird. Ausgangspunkt der Untersuchungen war die Beobachtung, dass die K+-Aufnahme über das Kdp-System bei K+-Konzentrationen >5 mM inhibiert wird. Diese wichtige Eigenschaft des Kdp-Systems wurde in der Vergangenheit häufig übersehen, da die Inhibierung des Kdp-Systems bei höheren pH-Werten (pH 7,8) durch eine hohe Rate unspezifischen K+-Transports kompensiert und somit überdeckt wird. Es konnte gezeigt werden, dass einzelne Aspartat-Substitutionen in den periplasmatischen Schleifen der Sensor-Domäne von KdpD ausreichten, um die Inhibierung des Kdp-Systems bei höheren K+-Konzentrationen aufzuheben. Diese KdpD-Derivate zeigten eine, im Vergleich zum KdpD-WT, veränderte Regulation der kdpFABC-Expression bei K+-Konzentrationen >5 mM, die eine adäquate K+-Aufnahme via KdpFABC ermöglichte. Diese Ergebnisse zeigen, dass die Inhibierung der K+-Aufnahme über das Kdp-System bei K+-Konzentrationen >5 mM auf einer Inhibierung der kdpFABC-Expression durch KdpD basiert. Weiterhin konnte gezeigt werde, dass eine Abnahme der extrazellulären K+-Konzentration eine effiziente und sofortige Stimulierung der KdpD/KdpE-Signaltransduktion bewirkt. Aus diesen Ergebnissen wurde geschlussfolgert, dass die extrazelluläre K+-Konzentration als Reiz für die Sensorkinase KdpD dient. Im zweiten Teil dieser Arbeit erfolgte erstmals eine absolute Quantifizierung von KdpD und KdpE, sowie der Untereinheiten des KdpFABC-Komplexes unter induzierenden und nicht-induzierenden Bedingungen mittels hoch-sensitiver und selektiver Massenspektrometrie. Unter nicht-induzierenden Bedingungen liegt die KdpFABC-Synthese in der gleichen Größenordnung wie die KdpD- und KdpE-Synthese vor. Dieser Befund ist eine wichtige Voraussetzung für die postulierte, regulatorische Interaktion zwischen der Sensorkinase KdpD und der K+-Transportuntereinheit KdpB (Kipschull, 2011). Unter induzierenden Bedingungen stieg die KdpFABC-Synthese 100-300-fach, während eine etwa 10-fache Erhöhung der KdpD- und KdpE-Synthese nachgewiesen werden konnte. Diese Beobachtung bestätigt, dass das Zweikomponenten-System KdpD/KdpE unter induzierenden Bedingungen einer Autoregulation unterliegt. Die Autoregulation konnte durch eine räumliche Trennung des kdpFABC- und kdpDE-Operons aufgehoben werden. Die Aufhebung der Autoregulation von KdpD/KdpE hatte jedoch keinen Einfluss auf die Expressionskinetik des kdpFABC-Operons unter induzierenden Bedingungen. Der dritte Teil dieser Arbeit beschreibt die Konstruktion eines E. coli-Stamms, der eine vollständige Deletion des kdpD-Gens trägt. Nach einer zeitlichen Verzögerung konnte in dem daraus resultierenden E. coli-Stamm (LB2240ΔkdpD) unter K+-Limitation eine KdpD-unabhängige Expression des kdpFABC-Operons nachgewiesen werden. Die kdpFABC-Expression befähigte diesen Stamm, in Abwesenheit von KdpD unter K+-Limitation zu wachsen. Es konnte gezeigt werde, dass das K+-limitierte Wachstum von LB2240ΔkdpD eine Phosphorylierung von KdpE voraussetzt, wobei Acetylphosphat nicht als alternativer Phosphodonor diente. Da nur wenige Zellen einer LB2240ΔkdpD-Kultur den beschriebenen Phänotyp zeigten, liegt die Vermutung nahe, dass diese Zellen Träger einer Suppressormutation sind, die eine KdpD-unabhängige Phosphorylierung von KdpE und daraus folgend eine kdpFABC-Expression verursacht.

In dieser Arbeit konnten mittels des BACTH-Systems Interaktionen des kompletten KdpD Proteins sowie der N-terminalen Domäne (KdpD1-395) mit den N- und C-terminalen (KdpD396-894) Domänen von KdpD nachgewiesen werden. Darüber hinaus wurde der Zusammenhang zwischen dem Interaktionsverhalten und den Phänotypen bestimmter Punktmutations- und Deletionsmutanten von KdpD untersucht, jedoch konnte eine solche Abhängigkeit nicht bestätigt werden. Die Lokalisation von KdpD-GFP wurde in dem kdpD-Teildeletionsstamm TKV2208 untersucht, in dem sich das Hybridprotein membrangebunden in einem gepunkteten Verteilungsmuster entlang des Zellkörpers nachweisen lässt. Besonders interessant ist das häufige Vorkommen spiralförmiger KdpD-GFP Strukturen, welche sich entlang des Zellkörpers zeigen. Daher wurde eine Beeinflussung der Lokalisation von KdpD-GFP durch MreB vermutet. Eine Behandlung der Zellen mit der Verbindung A22 veränderte die Proteinverteilung jedoch nicht. Daher ist anzunehmen, dass die KdpD-GFP Lokalisation in E. coli MreB-unabhängig erfolgt. Des Weiteren wurde eine Beeinflussung der Lokalisation des Hybridproteins durch das Penicillin-Bindeprotein 3 in Erwägung gezogen. Um diese Möglichkeit zu evaluieren wurde PBP3 mit Cephalexin spezifisch gehemmt. Jedoch konnte kein Unterschied zur vorher aufgeführten Lokalisation von KdpD-GFP beobachtet werden. Ein weiterer Aspekt der Lokalisationsstudien war, ob Cardiolipin einen Einfluss auf die KdpD-GFP Lokalisation hat. Für diese Fragestellung wurde der Stamm UE54 benutzt, welcher kein Cardiolipin synthetisieren kann. Es konnte gezeigt werden, dass Cardiolipin keinen Einfluss auf die Lokalisation von KdpD-GFP zu haben scheint. Darüber hinaus wurde die Abhängigkeit der KdpD-GFP Lokalisation von SecB und SecG mittels Deletionsmutanten getestet. Die Deletion dieser beiden Sec-Translokationsproteine führte jedoch zu keiner Veränderung der Lokalisation von KdpD-GFP.

In dieser Arbeit wurde untersucht, ob Kalium-Limitation die Zusammensetzung der Phospholipide der Membran in Escherichia coli beeinflusst. Dabei standen mögliche Auswirkungen auf die Expression des kdpFABC-Operons im Vordergrund. Die Regulation der Expression dieses Operons erfolgt durch die Sensorkinase KdpD und den Antwortregulator KdpE. Während die Signalkaskade aufgeklärt ist, wird der Stimulus, den KdpD wahrnimmt, nach wie vor kontrovers diskutiert.

Salmonella enterica is a worldwide food-borne pathogen, which regularly causes large outbreaks of food poisoning. Recent outbreaks linked to consumption of contaminated foods with low water-activity, have raised interest in understanding the factors that control fitness of this pathogen to dry environment. Consequently, the general objective of this study was to extend our knowledge on desiccation tolerance and long-term persistence of Salmonella. We discovered that dehydrated STm entered into a viable-but-nonculturable state, and that addition of chloramphenicol reduced bacterial survival. This finding implied that adaptation to desiccation stress requires de-novo protein synthesis. We also discovered that dried STm cells develop cross-tolerance to multiple stresses that the pathogen might encounter in the agriculture/food environment, such as high or low temperatures, salt, and various disinfectants. These findings have important implications for food safety because they demonstrate the limitations of chemical and physical treatments currently utilized by the food industry to completely inactivate Salmonella. In order to identify genes involved in desiccation stress tolerance, we employed transcriptomic analysis of dehydrated and wet cells and direct screening of knock-out mutant and transposon libraries. Transcriptomic analysis revealed that dehydration induced expression of ninety genes and down-regulated seven. Ribosomal structural genes represented the most abundant functional group with a relatively higher transcription during dehydration. Other large classes of induced functional groups included genes involved in amino acid metabolism, energy production, ion transport, transcription, and stress response. Initial genetic analysis of a number of up-regulated genes was carried out). It was found that mutations in rpoS, yahO, aceA, nifU, rpoE, ddg,fnr and kdpE significantly compromised desiccation tolerance, supporting their role in desiccation stress response.