VAAM-Jahrestagung 2012 18.–21. März in Tübingen

54protein is reversibly uridylylated by the signal transducing enzymeUTase/UR. The PII protein then regulates the activity of the twodownstream covalent modification cycles. PII is one of the most widelydistributed proteins in nature, and it appears to be universally involved incontrolling nitrogen assimilation.I will discuss biochemical studies that indicated that PII is the sensor of thea-ketoglutarate signal and of the adenylylate energy charge signal, whichare antagonistic, and will review our current understanding of the signalingmechanisms. I will also discuss biochemical studies describing thesensation of glutamine by two of the signal-transduction enzymes of thesystem. Finally, I will review recent studies that revealed factorsinfluencing the sensitivity of responses to the glutamine signal. Together,these results will provide a basic overview of the control of nitrogenassimilation in E. coli.ISV12Signalling in biofilm formation of Bacillus subtilisJ. StülkeGeorg-August University, Allgemeine Mikrobiologie, Göttingen, GermanyCells of Bacillus subtilis can either be motile or sessile, depending on theexpression of mutually exclusive sets of genes that are required foragellum or biolm formation, respectively. Both activities arecoordinated by the master regulator, SinR. We have identified three novelfactors that are required for biofilm formation, the transcription factorCcpA, the novel RNase Y and the previously uncharacterized YmdBprotein. Since YmdB had not been studied before, we analyzed thecorresponding mutant in more detail. We observed a strong overexpressionof the hag gene encoding agellin and of other genes of the SigDdependentmotility regulon in the ymdB mutant, whereas the two majoroperons for biolm formation, tapA-sipW-tasA and epsA-O, were notexpressed. As a result, the ymdB mutant is unable to form biolms. Ananalysis of the individual cells of a population revealed that the ymdBmutant no longer exhibited bistable behavior; instead, all cells are shortand motile. The inability of the ymdB mutant to form biolms issuppressed by the deletion of the sinR gene encoding the master regulatorof biolm formation, indicating that SinR-dependent repression of biolmgenes cannot be relieved in a ymdB mutant. Our studies demonstrate thatlack of expression of SlrR, an antagonist of SinR, and overexpression ofSlrR suppresses the effects of a ymdB mutation.ISV13No abstract submitted!ISV14No abstract submitted!ISV15Suppression of Clostridium difficile disease and transmissionby the intestinal microbiotaA.W. WalkerWellcome Trust Sanger Institute, Pathogen Genomics Group, Hinxton,United KingdomThe human large intestine plays host to an extremely abundant and diversecollection of microbes, which are collectively termed the intestinalmicrobiota. Under normal circumstances our resident microbes areconsidered to play a number of key roles in the maintenance of humanhealth. One example is the establishment of a phenomenon termed“colonization resistance”. During health, or in the absence of antibioticuse, our indigenous microbiota can effectively inhibit colonization andovergrowth by invading “foreign” microbes such as pathogens. In doing soour microbiota helps to protect us from gastrointestinal infection and alsoacts to keep potentially pathogenic indigenous species such as Clostridiumdifficile under control. Colonization resistance against C. difficile istypically broken by broad-spectrum antibiotic use, which disrupts thedensity, composition and activity of the intestinal microbiota and allowsthe pathogen to proliferate in the intestine and cause disease. Using amouse model of disease we monitored longitudinal shifts in microbiotacomposition in an attempt to better understand the underlying dynamicsbehind antibiotic-associated C. difficile infection and transmission. Wefind that infection with certain strains of C. difficile results in prolongedshedding of C. difficile spores, which occurs in tandem with inhibited reestablishmentof colonization resistance. This leads to enhancedtransmission of these strains and also mimics the situation observed inaround 25% of C. difficile cases in humans where the disease becomesrefractory to treatment and patients suffers constant relapses, even aftertreatment with strong antibiotics such as vancomycin. I will thereforedescribe more novel means of restoring bacterial diversity in the intestineand offer some perspectives on future challenges for developing therapiesto promote colonization resistance.ISV16Systems biology of halophilic archaeaD. OestherheltMax-Planck-Institut für Biochemie, Martinsried, GermanyExtreme halophiles from the branch of euryarchaeota live in very hostileenvironments characterized by intense radiation and shortage of nutrientsand oxygen. Halobacterium salinarum became a model organism to studyadaptation of life to these extreme conditions and cytoplasmic saltconcentrations of up to 5 M. After a general description of halophilicfeatures of these organisms specific example of systems biological modelsof intermediary metabolism, bioenergetics and signal transduction on thebasis of -omics data as well ass biochemical and behavioural experimentswill be presented.ISV17Microbial survival strategies: Staphylococcus aureus as ahighly effective surviverR. A. ProctorEmeritus Professor of Medical Microbiology/Immunology and Medicine.University of Wisconsin School of Medicine and Public Health, Madison, WI,United StatesS. aureus uses multiple strategies to survive from colonizing passively thehost to attacking the host defenses. S. aureus has traditionally beenconsidered a colonizer of the nose, but the newer methicillin resistantstrains (MRSA) have the capacity to colonize the throat, vagina, rectum,and skin. Once the skin is barrier is breached host cationic antimicrobialproteins (CAPs) are released from the keratinocytes, but S. aureus has atwo-component regulator, GraRS, which recognizes and confers resistanceto CAPs. Local resident inflammatory cells such as macrophages and mastcells can be circumvented by the organism being taken up into the host cellvia 51 integrin and eventually the cytoplasm thereby avoiding thebactericidal mechanisms of these professional phagocytes. S. aureus has avery wide variety of factors that block each stage of influx of neutrophils(PMNs) into the area of local infection. Those PMNs that do reach theinfected site can also have their bactericidal mechanisms circumvented sothat they too become a reservoir for S. aureus. Proliferation of thestaphylococci can result in local abscess formation wherein bacterialproteins such as coagulase can limit blood flow thereby reducing PMNinflux, ClfA and Eap can help in the formation of an abscess, and theanaerobic micro-environment will also reduce the effectiveness ofprofessional phagocytes. Other S. aureus can down-regulate theirvirulence factors by becoming small colony variants (SCVs) and deletingtheir agr and its associated virulence regulon. Although these organismsare much less aggressive, they are better able to enter a very wide varietyof host cells (including respirator and mammar epithelial cells, endothelialcells, fibroblasts, and keratinocytes), and persist because they fail to lyseor to produce apoptosis of the host cells, do not stimulate hypoxiainduciblefactor (HIF), and resist host cell CAPs. Phenotypic switching toSCVs has now been demonstrated in animal models, and these SCVsgenerate a much less robust immune response than their wild type parentstrains. In addition, these apparently less virulent variants show increasedexpression of adhesins, thereby allowing them to persist better on hosttissues. The ability of S. aureus to form biofilm is another mechanism forescaping host defenses. T cells have been recently implicated in thedefense against S. aureus infections, and T-cell angery is found in chronicinfections. Particularly worrying is the fact that multi-drug resistantstrains are now circulating that have enhanced ability to survive on skin, inthe lung, and kidneys. For example, resistance to linezolid has been linkedto point mutations in relA that allowed for the development of SCVs thatshowed an enhanced stringent response and persistent infection in patientsand animal models. The success of S. aureus as a pathogen certainlyrelates to the vast array of survival strategies.BDV001Setting the pace: Mechanisms controlling the temporalregulation of the Caulobacter crescentus cell cycleK. Jonas* 1 , M.T. Laub 1,21 Massachusetts Institute of Technology, Department of Biology,Cambridge MA, United States2 Massachusetts Institute of Technology, Howard Hughes Medical Institute,Cambridge MA, United StatesOne of the most fundamental processes in biology is the regulation of thecell cycle, involving DNA replication, chromosome segregation, and celldivision. The alpha-proteobacterium Caulobacter crescentus has emergedas an excellent model for studying the basic principles of cell cyclecontrol, largely owing to an ability to synchronize large populations ofcells. Additionally, Caulobacter divides asymmetrically, yielding daughtercells that differ with respect to their replicative fates and morphology. Thisintrinsic asymmetry has also made Caulobacter an attractive model forunderstanding spatial regulatory mechanisms. Our recent workBIOspektrum | Tagungsband 2012