VAAM-Jahrestagung 2011 Karlsruhe, 3.–6. April 2011

RGP039Comparison of different Escherichia coli K-12 laboratorystrains with respect to growth characteristics and biofilmformationA. Richter*, R. HenggeFree University, Berlin, GermanyWe systematically compared phenotypic traits of four commonly usedEscherichia coli K-12 strains: the nonmotile MC4100 (which carries anflhDC frame shift mutation) (1), the motile W3110 and two MG1655 strainswith different motility (affected by the presence or absence of IS elementsupstream of flhD) (2).The four strains grow differently in complex medium. They also showdifferences in cell length. RpoS is stationary phase-induced in all, butW3110 was found to exhibit higher RpoS levels. Colonies of W3110, butnot of the other strains, can form complex patterns of wrinkles and ringsunder some conditions. Formation of these structures requires motility,RpoS as well as regulatory and structural genes for adhesive curli fimbriae,but not cellulose formation, which could not be detected in any of the fourstrains. Curli fimbriae expression is different in the four strains. MC4100induced csgB::lacZ earlier during entry into stationary phase, since it doesnot express the RpoS antagonist FliZ, which is under FlhDC control anddetermines the timing of csgB::lacZ expression in the highly motile strainsW3110 and MG1665. The low-motility variant of MG1665 showed normaltiming but reduced levels of csgB::lacZ expression. Interestingly, neitherRpoS nor curli formation are required for W3110 and MG1655 to formbiofilms in the standard crystal violet assay in polystyrole microtiter plates(MC4100 does not form a biofilm at all). This confirms that E. coli can formdifferent types of biofilms dependent on different regulatory genes andstructural components.Overall, our work shows that the commonly used laboratory strains of E.coli K-12 differ in characteristics like motility, stress gene expression andcomplex biofilm formation. Overall, W3110 may be the strain with the mostoptimal combination of these complex traits. Moreover, our data suggestthat care should be taken in generalizing results obtained with only one ofthese four strains.[1] Ferenci, T. et al (2009): Genomic sequencing reveals regulatory mutations and recombinationalevents in the widely used MC4100 lineage of Escherichia coli K-12. J Bacteriol. 191: 4025-4029.[2] Barker, C. S. et al (2004) Increased motility of Escherichia coli by insertion sequence elementintergration into the regulatory region of the flhD operon. J Bacteriol. 186: 7529-7537.RGP040Induction dynamics of quorum sensing in Pseudomonasputida colonies under flow conditionsB. Hense* 1 , A. Meyer 2 , C. Kuttler 3 , J. Müller 3 , J. Megerle 2 , J. Rädler 21 Institute of Biomathematics and Biometry, Helmholtz Center Munich,Neuherberg/Munich, Germany2 Department für Physik und CeNS, Ludwig Maximilians-University,Munich, Germany3 Center for Mathematical Science, Technical University Munich,Garching/Munich, GermanyBacterial communication via release and sensing of signal molecules(autoinducer, AI) has been mainly investigated in batch cultures. Hereusually coordinated, synchronous response of the whole population isinduced in a cell density dependent manner (quorum sensing, QS). However,most bacteria live heterogeneously distributed in aggregates or biofilmsattached to surfaces. Under these conditions, functionality of the signallingsystem is less well understood and more difficult to approachexperimentally. We thus use a combined experimental/mathematicalmodelling strategy to investigate the induction dynamics of the PpuI/R QSsystem in Pseudomonas putida IsoF. Induction of AI controlled expressionof a gfp gene was followed with high spatio-temporal (single cell or colonylevel) resolution. The influence of flow respectively addition of external AIwas examined. Main results were: Mass transfer (flow) delays the inductionbehaviour, probably by removal of AIs. A compartmentation of yet unkownorigin occurs, limiting the influence of AI from outside the colony. ÁIregulation promoted intra- as well as intercolonial heterogeneity.Summarized, there were fundamental differences between the AIfunctionality in cell aggregates and planktonic batch cultures, which havebeen analysed before [1]. These differences have consequences for theecological functionality of autoinducers.RGP041Characterization of mutations in the sensor kinase geneof the two-component system CiaRH in clinicalStreptococcus pneumoniae strainsP. Marx*, M. Müller, R. Hakenbeck, R. BrücknerDepartment of Microbiology, University of Kaiserslautern, Kaiserslautern,GermanyThe two-component regulatory system CiaRH (competence induction andaltered cefotaxime susceptibility) of Streptococcus pneumoniae affects avariety of processes such as β-lactam resistance, competence development,autolysis, bacteriocin production, and virulence.The response regulator CiaR directly controls the expression of 24 genesorganized in 15 transcriptional units. Besides 19 protein coding genes, CiaRcontrols the expression of 5 small non-coding RNAs.Mutations in the histidine kinase gene ciaH have been identified inspontaneous β-lactam resistant mutants of Streptococcus pneumoniae R6, anon-pathogenic laboratory strain. Gene expression analyses of the promotersdirectly controlled by CiaR revealed that the CiaR response regulator ismore active in strains with altered kinase genes. Furthermore the mutationsin these strains lead to decreased susceptibility to β-lactam antibiotics,prevent development of spontaneous genetic competence, and lead to adelayed autolysis during stationary growth.In contrast to the detailed characterization of the CiaRH system in thelaboratory strain R6, CiaRH-mediated regulation has hardly been studied inclinical isolates of S. pneumoniae. The ciaH mutations appeared even to berestricted to mutants isolated in the laboratory. However, new ciaH allelesare present in S. pneumoniae genome sequences that became recentlyavailable. To test their functions, they were introduced into S. pneumoniaeR6 and CiaR-mediated regulation was analyzed. The results of theseexperiments clearly showed that most of these new ciaH alleles indeedactivated the CiaR regulon. Therefore, mutations in ciaH apparentlycontribute to advanced fitness under antibiotic conditions not only inlaboratory but also in nature.RGP042The phytochrome regulon of Pseudomonas aeruginosaS. Heine* 1 , K. Barkovits 1 , M. Scheer 2 , N. Frankenberg-Dinkel 11 Physiology of Microorganisms, Ruhr-University Bochum, Bochum,Germany2 Institute of Microbiology, University of Technology, Braunschweig,GermanyPhytochromes are red/far-red light sensitive photoreceptores. First they werediscovered in plants, but later on they have also been detected in fungi,cyanobacteria and other prokaryotes. In plants phytochromes control a widevariety of developmental processes, however, in prokaryotes the functionsare widely unknown. Most bacterial phytochromes contain a histdine-kinasedomain suggesting that signal transduction occurs via a two-componentregulatory system. Pseudomonas aeruginosa is one of the first heterotrophicbacteria in which a phytochrome has been identified. With the two genesbphO and bphP P. aeruginosa owns the two necessary components toassemble a red-light photoreceptor system: bphO codes for the hemeoxygenease to generate the chromophore biliverdin IXα and bphP, encodingthe apo-phytochrome. So far, no corresponding phytochrome responseregulator has been identified yet.bphO and bphP form a bicistronic operon whose expression is controlled bythe alternative sigma factor RpoS. New analyses provide a hint for anadditional regulation of bphP. To investigate the function of bphO and bphPchromosomal knock-out mutants were constructed and analysed. However,no significant phenotypical difference between the mutants and wild typewere observed. A combination of expression profile experiments andproteome analyses revealed a link to a bphP-mediated stress response. Themost downregulated gene PA4739 (osmY) is used in a genetic screen toidentify the corresponding response regulator of BphP to gain further insightinto the function of the phytochrome in P. aeruginosa and the componentsof its regulon.[1] Fekete, A. et al (2010): FEMS Microbiol. Ecol. 72, 22-34.spektrum | Tagungsband 2011