Biochemistry of pathogenic bacteria: Isobacteriochlorin heme d1 biosynthesis in Pseudomonas aeruginosa

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Anaerobic growth and survival of Pseudomonas aeruginosa is essential for biofilm formation and infection. Replacement of the electron acceptor oxygen by nitrate during anaerobic denitrification (NO3-  NO2-  NO  N2O  N2) is a powerful strategy for anaerobic energy generation and ecologically indispensable for the global nitrogen cycle. In the second step of the denitrification process the dissimilatory nitrite reductase (cytochrome cd1) utilizes the prosthetic groups heme c and heme d1 for the reduction of NO2- to NO. Heme d1 is not a real heme, rather an isobacteriochlorin related to siroheme, vitamin B12 and coenzyme F430. The multistep biosynthesis of this unique cofactor is only poorly understood. This proposal focuses on the investigation of the biosynthetic raute leading to the formation of heme d1 in P. aeruginosa. The main objectives are the identification of biosynthetic intermediates and the elucidation of the catalytic properties of involved enzymes. For the stepwise identification of involved metabolites and enzymes available mutants of the involved nirCFDLGHJEN genes will be physiologically, genetically and biochemically characterized. Selected recombinant Nir proteins will be subjected to thorough biochemical and biophysical characterization to deduce their catalytic properties. Since heme d1 biosynthesis reconstitutes a unique bacterial target the impact of genetic pathway disruption on biofilm formation and infection are of general medical interest.