Magdeburg, Universiẗat, Diss., 2003.

Bacillus subtilis, une bactérie Gram-positive présente dans le sol, peut lorsque les nutriments sont en concentrations limitantes, sporuler, former des biofilms ou devenir compétente. La compétence est, chez B. subtilis, caractérisée par un arrêt de la division cellulaire, une tolérance aux antibiotiques et l'expression de plus d'une centaine de gènes. L'expression de la compétence, aussi désignée sous le nom de " K-state ", est dépendante de la synthèse du facteur de transcription ComK et se fait de façon stochastique résultant en la formation de deux sous-populations bactériennes, non-compétentes et compétentes. L'émergence, à partir de cellules génétiquement identiques, de deux sous-populations distinctes est une stratégie de survie très répandue chez les procaryotes, connue sous le nom de " bet-hedging ". Bien que les mécanismes de régulation du développement de la compétence ont, chez B. subtilis, largement été étudiés au cours des dernières années, la raison pour laquelle les souches non-domestiques sont très peu transformables (1-2% de la population) comparé aux souches domestiques (~15%) reste méconnue. Nous démontrons ici que c'est essentiellement dû à une mutation de transition dans le promoteur du gène degQ. Cette mutation diminue la synthèse de DegQ, protéine impliquée dans la régulation de la formation de biofilms, de la synthèse d'exoprotéases et de la transformation génétique. DegQ est une protéine impliquée dans le transfert d'un groupe phosphoryl entre la kinase DegS et son substrat DegU. Une faible quantité de DegQ diminue la concentration en DegU~P ce qui a pour conséquence la désinhibition de l'opéron srfA entrainant une accumulation de ComK et l'expression de la compétence. C'est ainsi que, dans les souches domestiques de B. subtilis, un plus grand nombre de bactéries atteignent le niveau nécessaire en ComK pour activer une boucle d'auto-activation transcriptionnelle de comK. Nous démontrons aussi que l'activation transcriptionnelle de srfA est, dans les souches non-domestiques, transitoire alors que la population bactérienne entre en phase stationnaire de croissance. Ces données indiquent que le développement de la compétence est moins fréquent et plus transitoire dans les souches non-domestiques de B. subtilis. De plus, cette limitation du K-state dans les souches non-domestiques est plus importante que précédemment " pensé " probablement dû à la domestication de B. subtilis au cours de ces 50 dernières années. Ce travail reflète non seulement, l'importance de l'utilisation de souches non-domestiques dans la caractérisation des voies de régulation de la compétence chez B. subtilis, mais aussi la portée du choix de modèle biologique dans l'étude de phénomènes biologiques complexes. / Bacillus subtilis, a Gram-positive soil bacterium, can enter into several developmental pathways such as sporulation, biofilm formation and competence development for DNA transformation when it becomes limited for essential nutrients. During competence, cells do not divide, are tolerant to antibiotics and competent cells express more than a 100 genes. The competent state has been named the K-state after its master regulator ComK. In B. subtilis, the entry into the K-state is stochastically determined by the activation of the transcription factor ComK and occurs, in the domesticated strains of B. subtilis, in approximately 15% of the population. The emergence from genetically identical cells of two distinct subpopulations (competent cells and non-competent cells) is known to be a classic survival strategy for bacteria, known as bet-hedging. Regulation of entry into the K-state has been intensively studied and is well understood; however, the reasons why undomesticated isolates of B. subtilis are poorly transformable compared to the domesticated strains remained unexplained. We show here that fewer cells enter the K-state, suggesting that some regulatory pathway limiting its expression has been lost in the domesticated backgrounds. We demonstrate that this is largely due to an inactivating point mutation in the degQ promoter region resulting in a decrease of the amount of DegQ. DegQ is known to stimulate phosphate transfer from the DegS autokinase to its cognate response regulator DegU. A low level of DegQ thus decreases the concentration of the phosphorylated form of DegU, leading to the de-repression of the srfA operon, which increases the amount of ComS leading to the stabilization of ComK. Thus, in domesticated strains of B. subtilis, more cells reach the concentration threshold of ComK needed to activate the positive auto-regulatory loop of ComK acting on its own promoter. We also show that the activation of srfA transcription in undomesticated strains is transient, as it is turned off when cells enter the stationary phase. Taken together, these data indicate that the K-state and transformability are less frequent and more transient in the undomesticated strains of B. subtilis. Consideration of the regulatory mechanisms and the fitness advantages and costs of the K-state must from now on take these features into consideration. These results underscore that our understanding of real-life biology requires the use of wild isolates.

This thesis examined the odiferous nature of rodent saliva for the male Mongolian gerbil, male and diestrous female golden hamsters, and male and female degus. Within each species,like-sexed pairs were dichotomized as to dominance or submissiveness and individual animals were presented with salivary samples from dominant pairings, an opposing gender, and a saline control; in an open field arena. Both degus and gerbils did not show any discriminative responding, via sniffs, time spent in proximity of and approaches to allstimuli. Degus discriminated salivary stimuli over the control when allowed to contact the stimuli. Degus preferred, via approaches, female samples. Male hamsters discriminated amongst all stimuli for the three behavioral measures. Dominant males preferred other male cues over diestrous female and saline samples via sniff. For approaches, dominant males preferred other dominant cues over submissive or female cues. Submissives preferred all salivary cues over the control via sniffs, but showed no individual preferences amongst the salivary cues. Female hamsters discriminated amongst all stimuli via sniffs. Dominant females preferred other submissive samples over those of a male and preferred dominant and submissive samples over the control, submissive females preferred all three salivary cues over the control; no other preferences were found. The importance of salivary cues and the odiferous nature of chemical cues of all secretory by-products of rodents are discussed.

Bacillus amyloliquefaciens FZB42 ist ein grampositives Bakterium, das in der Rhizosphäre das Pflanzenwachstum fördert (PGPR - Plant Growth Promotion) und pathogene Organismen hemmt. Abgesehen von dieser Fähigkeit produziert es eine Vielzahl von sekundären Metaboliten, die sowohl ribosomale als auch nicht-ribosomale Peptide umfassen. In dieser Arbeit erfolgte die Untersuchung der transkriptionellen Aktivierung und Regulation der Bacilysin- Biosynthese an den Promotoren der bac- und ywfH- Gene. Durch 5´-Deletionsanalysen wurde der Promotor von Bacilysin identifiziert. Die A (Sigmafaktor A) - abhängige Transkription startet über die konservierten Promotorelemente (-10 und -35) von den bac- und ywfH Genen. Die Untersuchungen der Promotoraktivitäten vom Wildtyp und den erzeugten Regulationsmutanten erfolgten über in vivo ß-Galaktosidase-(Reporter)-Assays. Die Ergebnisse der Reporter-Aktivitäten zeigten, dass Transkriptionsregulatoren die Expression der Bacilysin- Gene aktivieren. Mehrere globale Regulatoren wie DegU, ComA, Hpr und AbrB beeinflussen die Genexpression. In dieser Arbeit wurde mithilfe von DNaseI Footprinting-Analysen die DegU-Bindung an die bac- und ywfH- Promotoren bestätigt.Die negative Regulation der Bacilysin-Biosynthese wird durch den Regulator der transienten Phase Hpr bewerkstelligt. Eine direkte Hpr-Bindung an bac Promotor wurde mit DNaseI Footprint-Analysen gezeigt. Der Promotor des monocistronischen Gens ywfH wurde aber durch Hpr nicht beeinflusst. Die anderen Transkriptionsregulatoren, wie ComA und AbrB, regulieren die Genexpression von Bacilysin indirekt über DegQ und Hpr. In dieser Arbeit konnte demonstriert werden, dass der globale Regulator AbrB den Promotor vom hpr-Gen direkt kontrolliert. Zusammenfassend liefert diese Studie neue Informationen über die genetische Regulation der Bacilysin- Biosynthese in B. amyloliquefaciens FZB42. / Bacillus amyloliquefaciens FZB42 is a Gram-positive, pathogen-suppressing and plant-growth promoting rhizobacterium. Apart from this ability, it produces a vast array of secondary metabolites, which includes both ribosomal and non-ribosomal peptides. In this work, the transcriptional activation and regulation of bacilysin biosynthesis were studied at the promoters of bac and ywfH genes. The promoter of bacilysin was identified using 5''-deletion analysis. Sigma factor A (σA) was found to start transcription via conserved promoter elements (-10 and -35) of bac and ywfH genes. lacZ reporter fusion studies were performed in wild type and regulatory mutants. The results show the involvement of transcriptional regulators to activate the expression of bacilysin genes. Several global regulators such as DegU, ComA, Hpr and AbrB were identified and found to influence gene expression. In particular, I confirmed DegU binding in bac and ywfH promoters using radioactive DNase I footprinting. Furthermore, Hpr, a transition state regulator was found negatively to control bacilysin biosynthesis. Hpr binding to bac promoter was demonstrated using radioactive DNase I footprinting. Remarkably, Hpr does not influence the promoter of the monocistronic gene, ywfH. The other transcriptional regulators, such as ComA and AbrB, were correlated indirectly to affect the gene expression of bacilysin via DegQ and Hpr, respectively. The gene regulation of hpr was studied in this work. It was demonstrated that AbrB, a global regulator, directly controls the promoter of the hpr gene. However, the consensus sequence for AbrB binding was not identified, since it covers the entire promoter region in the DNA-protein interaction study. To conclude, this study provides new information regarding the genetic regulation of bacilysin biosynthesis in B. amyloliquefaciens FZB42.

No description available.