Catabolite repression in Pseudomonas aerugiosa

Pseudomonas aeruginosa is a versatile microorganism, which grows in soil, in water and on plants, and its aliphatic amidase contributes to this traits. The aliphatic amidase in P. aeruginosa assimilates short chain aliphatic amides to the corresponding acid and ammonia, which can be used as nutrients (i.e. as carbon and nitrogen source). However, aliphatic amides are not the preferred carbon source for P. aeruginosa, as the metabolic energy derived from acetamide degradation is modest. This is the reason why Pseudomonas (and bacteria in general) use mechanisms to repress the assimilation of non-preferred carbon sources until the preferred one (for P. aeruginosa: succinate) is consumed. This mechanism is called catabolite repression (CR). Our previous results have shown that the two component regulatory system CbrA/B, which senses differences in the carbon to nitrogen ratio, activates the expression of the sRNA crcZ. CrcZ binds to the catabolite repression control protein Crc, the major translational regulator in P. aeruginosa`s CR, and antagonizes the negative function of Crc on target gene expression by sequestering this protein. Besides its predominantly environmental lifestyle, P. aeruginosa is an opportunistic human pathogen, which causes serious infections in patients with cystic fibrosis, cancer or severe burn wounds. P. aeruginosa infections are difficult to eradicate because of its resistance towards many commonly used antibiotics and its ability to form biofilms. The aim of this project is to characterize the Cbr/Crc pathway as a new regulatory system of CR in P. aeruginosa. I will investigate the binding specificity of Crc to the sRNA CrcZ and to target mRNAs (e. g. amiE). Furthermore, I will determine whether a second putative Crc-like protein (PA4172) is involved in CR. In addition, the global regulator Hfq as a possible activator of crc and crcZ expression will be studied. Since most regulatory effects of Hfq are mediated by sRNAs, I will attempt to search for novel sRNAs which are implicated in CR. In addition, I will identify new targets of the Cbr/Crc system, especially those which are involved in biofilm formation and virulence of P. aeruginosa. This study should contribute to a better insight into the global carbon regulation of P. aeruginosa. Since CR is involved in virulence gene regulation as well as in the synthesis of enzymes important for degradation of toxic aromatic compounds, this project might impact on medical aspects of Pseudomonas infections as well as on Pseudomonas biodegradation.