Claudia Hase
Pathogenesis of Vibrio cholerae
RESEARCH
Pathogenic species have to deal with a wide range of environments both within and outside the host and most have elaborate regulatory circuits to ensure the correct temporal and spatial expression of virulence factors. However, in most cases the primary clues used by the bacteria to determine whether they are in the host and the mechanisms by which this sensing occurs are not well understood. Vibrio cholerae is the causative agent of the potentially lethal epidemic diarrheal disease cholera. Na+ -based bioenergetics plays an important role in both the environmental and infectious phases of this organism. We recently reported the first example for an intimate connection between the expression of the main virulence factors and the sodium membrane bioenergetics in V. cholerae. It is conceivable that changes in the chemiosmotic sodium cycle are the primary signals that this organism uses to determine whether it is in the extra-host environment or the human gut. The objective of our research is the detailed molecular characterization of the observed linkage between transmembrane Na+ circulation and virulence in V. cholerae. Our experimental design is based on the combination of methods of classical membrane bioenergetics with the powerful tools of modern molecular genetics. Such an interdisciplinary approach will yield results that would be vitally important not only for the case of V. cholerae but also for the better understanding of regulation of virulence in various pathogenic microorganisms.
The recent completion of many bacterial genome sequences revealed the presence of genes encoding various sodium-dependent systems in orgamisms, including some that were not known to have a primary sodium cycle of energy. Analysis of bacterial genome sequences shows that many human and animal pathogens encode primary membrane Na+ pumps and a number of Na+-dependent permeases. This indicates that these bacteria can utilize Na+ as a coupling ion instead of, or in addition to the H+ cycle. This capability to use a Na+ cycle may well be an important virulence factor for some pathogens and could provide a target for development of a novel intervention strategy. Indeed, the recent discovery of an effective natural antibiotic, korormicin, targeted against the Na+-translocating NADH:ubiquinone oxidoreductase, NQR, suggests the potential use of Na+ pumps as a drug target. Moreover, anti-microbial potential of other inhibitors of the Na+ cycle, such as monensin, Li+ and Ag+ ions, and amiloride derivatives have been previously reported. During this project we intend to construct and analyze defined mutants in Na+-extruding enzymes in V. cholerae as a first step towards a better understanding of this complex system in bacteria. The long-term goal is to identify novel drug targets amongst these enzymes and develop a potentially new class of anti-infectives to combat bacterial infections by pathogens that utilize sodium as a coupling ion. V. cholerae represents one of the best model organism for a comprehensive and detailed analysis of the sodium cycle of energy, as it has been experimentally demonstrated to utilize Na+ as a coupling ion and appears to possess a multitude of Na+-dependent systems.
SELECTED PUBLICATIONS
Häse CC, Mekalanos JJ. TcpP protein is a regulator of virulence gene expression in Vibrio cholerae. Proc Natl Acad Sci USA 95:730-734, 1998.
Häse CC, Mekalanos JJ. Effects of changes in membrane sodium flux on virulence gene expression in Vibrio cholerae. Proc Natl Acad Sci USA 96:3183-3187, 1999.
Häse CC, Judson N, Mekalanos JJ. Cholera. In, Encyclopedia of Microbiology (J. Lederberg, ed), 2nd Edition, Academic Press, pp 143-154, 2000.
Gosink KK, Häse CC. Requirements for the conversion of the Na+-driven flagellar motor of Vibrio cholerae to the H+-drive motor of Escherichia coli. J Bacteriol 182:4234-4240, 2000.
Häse CC. Virulence and sodium bioenergetics. Trends in Microbiol 8:490-491, 2000.
Häse CC, Barquera B. Role of sodium bioenergetics in Vibrio cholerae. Biochem Biophys Acta 1505:169-178, 2001.
Häse CC. Analysis of the role of flagella activity on virulence gene expression in Vibrio cholerae. Microbiol 147:831-837, 2001.
Barquera B, Häse CC, Gennis R. Expression and mutagenesis of the NqrC subunit of the NQR respiratory Na+-pump from Vibrio cholerae with covalently attached FMN. FEBS Lett. 492:45-49, 2001.
Brown II, Häse CC. Flagellum-independent surface migration of Vibrio cholerae and Escherichia coli. J Bacteriol 183:3784-3790, 2001.
Häse CC, Fedorova ND, Galperin, MY, Dibrov PA. Sodium Cycle in bacterial pathogens. Evidence from cross-genome comparisons. Microbiol Molec Biol Rev 65:353-370, 2001.
Barquera, B., P. Hellwig, W. Zhou, J.E. Morgan, C.C. Häse, K.K. Gosink, M. Nilges, P.J. Bruesehoff, A. Roth, C.R.D. Lancaster, and R.B. Gennis. Purification and characterization of the recombinant Na+-translocating NADH:quinone oxidoreductase from Vibrio cholerae. Biochemistry 41:3781-3791, 2002.
Gosink, K.K., R. Kobayashi, I. Kawagishi, and C. C. Häse. Analyses of the roles of the three cheA homologs in chemotaxis of Vibrio cholerae. J. Bacteriol 184:1767-1771, 2002.
Dibrov P, Dzioba J, Gosink KK, Häse CC. Chemiosmotic mechanism of the antimicrobial activity of Ag+ in Vibrio cholerae. Antimicrob Agents Chemother 46:2668-2670, 2002.
Dzioba J, Häse CC, Gosink K, Galperin MY, Dibrov P. Experimental verification of a sequence-based prediction: F1F0-type ATPase of Vibrio cholerae transports protons, not Na+ ions. J Bacteriol 185:674-678, 2003.
Häse CC. Ion motive force dependence of protease secretion and phage transduction in Vibrio cholerae and Pseudomonas aeruginosa. FEMS Microbiol Lett, 227:65-71, 2003