Postgenomic analysis of the Salmonella typhimurium cell envelope after exposure to cationic antimicrobial peptides

• Applicant: Dr. Martin Bader
• Subject Area: Metabolism, Biochemistry and Genetics of Microorganisms
• Term: from 2002 to 2007
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 5388006

Cationic antimicrobial peptides (CAMP) constitute a first barrier of the innate immune system by efficiently killing a wide spectrum of bacteria. CAMP bind to the lipopolysaccharid (LPS) moiety of the gram-negative outer membrane, thus dramatically increasing its permeability. In Salmonella typhimurium, reversible modifications of lipopolysaccaride lead to high levels of CAMP resistance. It has remained elusive whether these modifications are part of a global CAMP induced stress response. Here, I propose a proteomic approach to study the protein composition of the S. typhimurium cell envelope after its exposure to different CAMP classes, including polymyxins, a-helical peptides and defensins. Proteins, which are up- or downregulated under these stress conditions will be identified by two-dimensional gel electrophoresis and peptide mass fingerprinting. Expression of newly identified proteins will then be examined on the transcriptional level by generating gene fusions to a reporter gene. These fusion constructs will be further employed to screen for regulatory genes which respond to CAMP stress. To address the function of individual cell surface proteins, knockout mutants will be generated and tested for virulence in mice. These experiments are expected to lead to a better understanding of how gram-negative bacteria cope with the deleterious effects of antimicrobial peptides.

• DFG Programme: Emmy Noether International Fellowships
• Host: Professor Dr. Samuel I. Miller