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

53ISV07Teichoic acids in Gram-positive cell wall function and hostinteractionA. PeschelUniversitätsklinikum Tübingen, Medical Microbiology and HygieneDepartment, Tübingen, GermanyThe presence of teichoic acids or related polyanionic glycopolymers hasremained an enigmatic trait of most Gram-positive bacterial cellenvelopes. Recent advances in teichoic acids biosynthesis and theavailability of defined mutants now permit to explore the roles of teichoicacids, which exhibit extensive species or strain-specific differences incomposition and glycosylation but share polyanionic properties. Althoughnot essential to bacterial viability recent studies indicate that teichoic acidare crucial for directing cell envelope metabolism and turn-over and forgoverning the capacity of host-adapted Gram-positive bacteria to colonizeand infect mammalian host organisms. Therefore, teichoic acids representattractive targets for new antibacterial therapeutics against staphylococciand other Gram-positive human pathogens.ISV08Out of the iron age: the battle for zincJ. TommassenUtrecht University, Molecular Microbiology, Utrecht, NetherlandsThe cell envelope of Gram-negative bacteria consists of two membranes,which are separated by the periplasm containing the peptidoglycan layer.The outer membrane is an asymmetrical bilayer consisting ofphospholipids in the inner leaflet and lipopolysaccharides in the outerleaflet. It functions as a barrier for harmful compounds from theenvironment including many antibiotics. In contrast to the innermembrane, the outer membrane is not energized by a proton gradient andATP is not available in the periplasm. The lack of direct energy sourcesmay complicate transport processes across the outer membrane.Nevertheless, nutrients are taken up from the environment and proteins,including toxins and hydrolytic enzymes, are secreted.Most nutrients pass the outer membrane by passive diffusion via outermembrane proteins, collectively called porins, which form large openchannels in the outer membrane. Hence, in this case, energy availability isnot an issue. However, diffusion is an option only when the extracellularconcentration of the solute is high. The uptake of nutrients that are toodilute in the environment or whose size exceeds the exclusion limit of theporins is dependent on specific receptors and requires energy. The energysource utilized is the proton-motive force across the inner membrane,which is coupled to the transport process in the outer membrane via acomplex of three proteins, the TonB complex. The receptors involved arecalled TonB-dependent family (Tdf) members.In the vertebrate host, iron is sequestered by the iron-transport and -storageproteins transferrin and lactoferrin. Hence, the concentration of free iron isextremely low and restricts microbial growth, a mechanism known asnutritional immunity. Many Gram-negative pathogens respond to ironlimitation by the production and secretion of small iron-chelatingcompound, called siderophores, which bind ferric ions with very highaffinity. In addition, they produce Tdf receptors for the uptake of ferricsiderophorecomplexes. Other pathogens, including Neisseria meningitidis,do not produce siderophores, but they produce receptors for the ironbindingproteins of the host.Since efficient iron acquisition is an important virulence factor, it has beenstudied extensively in many pathogens. However, nutritional immunity inthe host is not restricted to iron limitation. Also other metals, includingzinc, manganese and nickel, can be limiting in the host, which responds toinfections by the production of metal-binding proteins, such asmetallothioneins and calprotectin. How these metals are transported acrossthe outer membrane is largely unknown.N. meningitidis normally lives as a commensal in the upper respiratorytract of up to 20% of the population but occasionally causes sepsis anmeningitis. A broadly cross-protective vaccine is not available. Thepresence of 12 Tdf receptors has been identified by analyzing the availablegenome sequences. Five of these receptors have well-defined roles in ironacquisition and their expression is induced under iron limitation.Microarray studies revealed that the expression of several other Tdfreceptors is unresponsive to iron availability; hence, we considered thepossibility that these receptors are involved in the uptake of other metals.We have studied the response of N. meningitidis to zinc limitation andfound that the expression of two Tdf receptors is specifically inducedunder those conditions. We have demonstrated that these receptors areinvolved in zinc acquisition and identified their ligands. The resultsdemonstrate how N. meningitidis evades nutritional immunity imposed bythe metal-binding proteins of the host. The receptors involved areattractive vaccine candidates.ISV09Origins and proliferation of L-form (cell-wall deficient)Bacillus subtilisP. Domínguez-Cuevas, R. Mercier, Y. Kawai, J. Errington*Newcastle University, Centre for Bacterial Cell Biology, Institute for Celland Molecular Biosciences, Newcastle upon Tyne, United Kingdom.The cell wall is a defining structure of bacterial cells. It provides aprotective outer shell and is crucial in pathogenesis as well as the target forimportant antibiotics. Synthesis of the wall is organised by cytoskeletalproteins homologous to tubulin (FtsZ) and actin (MreB). Because all majorbranches of the bacterial lineage possess both wall and cytoskeleton, thesewere probably present in the last common ancestor of the bacteria. L-formsare unusual variants of bacteria that lack the wall and are found in variousspecialised habitats, possibly responsible for a range of chronic andpersistent diseases. We have developed a model system for studying the L-form state in Bacillus subtilis (Leaver et al., 2009, Nature 457, 849-53).Molecular genetic analysis has revealed a number of discrete stepsrequired for the transition from the walled to the non-walled state(Domnguez-Cuevas et al., 2012, Mol Microbiol 83, 52-66). Unexpectedly,it has also shown that proliferation of L-forms is completely independentof the normally essential FtsZ or MreB cytoskeletal systems and occurs bya membrane blebbing or tubulation process. Genetic analysis has identifiedfactors required for proliferation of L-forms, and so far these results pointto membrane dynamics as being of critical importance. L-forms mayprovide an interesting model for considering how primitive cellsproliferated before the invention of the cell wall.ISV10Positive regulation of cell division site positioning in bacteriaby a ParA proteinL. Søgaard-AndersenMax-Planck-Institut für terrestrische Mikrobiologie, Marburg, Germany.In all cells, accurate positioning of the division site is essential forgenerating appropriately-sized daughter cells with a correct chromosomenumber. In bacteria, cell division generally occurs at midcell and initiateswith assembly of the tubulin homologue FtsZ into a circumferential ringlikestructure, the Z-ring, underneath the cell membrane at the incipientdivision site. Subsequently, FtsZ recruits the remaining components of thedivision machinery needed to carry out cytokinesis. Thus, the position ofZ-ring formation dictates the division site. Consistently, all known systemsthat regulate positioning of the division site control Z-ring positioning.These systems act as negative regulators to inhibit Z-ring formation at thecell poles and over the nucleoid, leaving only midcell free for Z-ringformation. Here we show that the ParA homologue PomZ positivelyregulates Z-ring positioning in Myxococcus xanthus. Lack of PomZ resultsin division defects, a reduction in Z-ring formation, and abnormalpositioning of the few Z-rings formed. PomZ localization is cell cycleregulated and culminates at midcell before and independently of FtsZsuggesting that PomZ recruits FtsZ to midcell. FtsZ alone does notpolymerize, however, FtsZ polymerization is directly stimulated by PomZin vitro. Thus, PomZ positively regulates positioning of the division site byrecruiting FtsZ and providing positional information for Z-ring formationand coupling it to cell cycle progression. Models will be discussed for howPomZ identifies midcell.ISV11Integration of signals in the regulation of bacterial nitrogenassimilationA.J. NinfaUniversity of Michigan Medical School, Department of BiologicalChemistry, Ann Arbor, MI, United StatesIn bacteria, nitrogen assimilation is coordinated with other aspects ofmetabolism and cellular energy status. Three major signals are known tocontrol the expression of nitrogen regulated genes and the activity of theenzyme glutamine synthetase, which plays a key role in the assimilation ofthe preferred nitrogen source, ammonia. These three signals are (i)glutamine, (ii) a-ketoglutarate, and (iii) the ratio of ATP to ADP, which isan indicator of the cellular adenylylate energy charge. In this presentation,I will review our understanding of how these signals function to controlnitrogen assimilation in Escherichia coli.The expression of nitrogen-regulated (Ntr) genes in E. coli is controlled bya cascade-type system consisting of two linked covalent modificationcycles, in which the downstream cycle is comprised of a two-componentregulatory system that directly controls gene expression. The regulation ofglutamine synthetase activity is also controlled by a cascade-type systemcomprised of two linked covalent modification cycles, in which thedownstream cycle is comprised of glutamine synthetase and the enzymethat controls its activity by reversible adenylylation. The two signallingsystems are connected, as the upstream cycle for both systems is the same.In this upstream covalent modification cycle, the PII signal transductionBIOspektrum | Tagungsband 2012