The opportunistic pathogen Pseudomonas aeruginosa utilizes a wide range of virulence factors to adapt to the host environment. With the antimicrobial pipeline drying up, understanding and targeting virulence factors for therapeutic development is an exciting alternative for the discovery of novel disease inhibitors. An integrated genome-wide transposon mutagenesis screening approach was performed in P. aeruginosa using multiple in vivo disease models with the aim to identify new virulence factors required for infection. A mutant attenuated in the production of multiple virulence determinants using in vitro assays was identified. This mutant also showed severe attenuation using in vivo models with up to an 80 % increased survival in murine chronic and acute lung infection models. The predicted protein coded by the mutated gene showed homology to nitrite and sulphite reductases. Using a methyl viologen reduction assay, we have shown that this gene encondes a nitrite reductase, operating in a siroheme and 4Fe-4S dependant manner. The preference for nitrite and the requirement of siroheme revealed that product of this gene is an assimilatory nitrite reductase and hence we propose it to be named as NirA. Work is now on-going to understand how NirA contributes to virulence and determine the crystal structure of this protein with a view to screen for novel inhibitors of this enzyme using a drug discovery platform available in our laboratories.

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