• Genomewide identification of genetic determinants of antimicrobial drug resistance in Pseudomonas aeruginosa.

      Dötsch, Andreas; Becker, Tanja; Pommerenke, Claudia; Magnowska, Zofia; Jänsch, Lothar; Häussler, Susanne; Chronic Pseudomonas Infections Research Group, Helmholtz Center for Infection Research, Inhoffenstrasse 7, D-38124 Braunschweig, Germany. (2009-06)
      The emergence of antimicrobial drug resistance is of enormous public concern due to the increased risk of delayed treatment of infections, the increased length of hospital stays, the substantial increase in the cost of care, and the high risk of fatal outcomes. A prerequisite for the development of effective therapy alternatives is a detailed understanding of the diversity of bacterial mechanisms that underlie drug resistance, especially for problematic gram-negative bacteria such as Pseudomonas aeruginosa. This pathogen has impressive chromosomally encoded mechanisms of intrinsic resistance, as well as the potential to mutate, gaining resistance to current antibiotics. In this study we have screened the comprehensive nonredundant Harvard PA14 library for P. aeruginosa mutants that exhibited either increased or decreased resistance against 19 antibiotics commonly used in the clinic. This approach identified several genes whose inactivation sensitized the bacteria to a broad spectrum of different antimicrobials and uncovered novel genetic determinants of resistance to various classes of antibiotics. Knowledge of the enhancement of bacterial susceptibility to existing antibiotics and of novel resistance markers or modifiers of resistance expression may lay the foundation for effective therapy alternatives and will be the basis for the development of new strategies in the control of problematic multiresistant gram-negative bacteria.
    • Global genotype-phenotype correlations in Pseudomonas aeruginosa.

      Pommerenke, Claudia; Müsken, Mathias; Becker, Tanja; Dötsch, Andreas; Klawonn, Frank; Häussler, Susanne; Chronic Pseudomonas Infections, Helmholtz Center for Infection Research, Braunschweig, Germany. (2010)
      Once the genome sequence of an organism is obtained, attention turns from identifying genes to understanding their function, their organization and control of metabolic pathways and networks that determine its physiology. Recent technical advances in acquiring genome-wide data have led to substantial progress in identifying gene functions. However, we still do not know the function of a large number of genes and, even when a gene product has been assigned to a functional class, we cannot normally predict its contribution to the phenotypic behaviour of the cell or organism--the phenome. In this study, we assessed bacterial growth parameters of 4030 non-redundant PA14 transposon mutants in the pathogenic bacterium Pseudomonas aeruginosa. The genome-wide simultaneous analysis of 119 distinct growth-related phenotypes uncovered a comprehensive phenome and provided evidence that most genotypes are not phenotypically isolated but rather define specific complex phenotypic clusters of genotypes. Since phenotypic overlap was demonstrated to reflect the relatedness of genotypes on a global scale, knowledge of an organism's phenome might significantly contribute to the advancement of functional genomics.
    • The Pseudomonas aeruginosa Chemotaxis Methyltransferase CheR1 Impacts on Bacterial Surface Sampling.

      Schmidt, Juliane; Müsken, Mathias; Becker, Tanja; Magnowska, Zofia; Bertinetti, Daniela; Möller, Stefan; Zimmermann, Bastian; Herberg, Friedrich W; Jänsch, Lothar; Häussler, Susanne; et al. (2011)
      The characterization of factors contributing to the formation and development of surface-associated bacterial communities known as biofilms has become an area of intense interest since biofilms have a major impact on human health, the environment and industry. Various studies have demonstrated that motility, including swimming, swarming and twitching, seems to play an important role in the surface colonization and establishment of structured biofilms. Thereby, the impact of chemotaxis on biofilm formation has been less intensively studied. Pseudomonas aeruginosa has a very complex chemosensory system with two Che systems implicated in flagella-mediated motility. In this study, we demonstrate that the chemotaxis protein CheR1 is a methyltransferase that binds S-adenosylmethionine and transfers a methyl group from this methyl donor to the chemoreceptor PctA, an activity which can be stimulated by the attractant serine but not by glutamine. We furthermore demonstrate that CheR1 does not only play a role in flagella-mediated chemotaxis but that its activity is essential for the formation and maintenance of bacterial biofilm structures. We propose a model in which motility and chemotaxis impact on initial attachment processes, dispersion and reattachment and increase the efficiency and frequency of surface sampling in P. aeruginosa.
    • The pseudomonas quinolone signal (PQS) balances life and death in Pseudomonas aeruginosa populations.

      Häussler, Susanne; Becker, Tanja; Department of Cell Biology, Helmholtz Center for Infection Research, Braunschweig, Germany. susanne.haeussler@helmholtz-hzi.de (2008)
      When environmental conditions deteriorate and become inhospitable, generic survival strategies for populations of bacteria may be to enter a dormant state that slows down metabolism, to develop a general tolerance to hostile parameters that characterize the habitat, and to impose a regime to eliminate damaged members. Here, we provide evidence that the pseudomonas quinolone signal (PQS) mediates induction of all of these phenotypes. For individual cells, PQS, an interbacterial signaling molecule of Pseudomonas aeruginosa, has both deleterious and beneficial activities: on the one hand, it acts as a pro-oxidant and sensitizes the bacteria towards oxidative and other stresses and, on the other, it efficiently induces a protective anti-oxidative stress response. We propose that this dual function fragments populations into less and more stress tolerant members which respond differentially to developing stresses in deteriorating habitats. This suggests that a little poison may be generically beneficial to populations, in promoting survival of the fittest, and in contributing to bacterial multi-cellular behavior. It further identifies PQS as an essential mediator of the shaping of the population structure of Pseudomonas and of its response to and survival in hostile environmental conditions.