Sigma factors in Pseudomonas aeruginosa

In Pseudomonas aeruginosa, as in most bacterial species, the expression of genes is tightly controlled by a repertoire of transcriptional regulators, particularly the so-called sigma (σ) factors. The basic understanding of these proteins in bacteria has initially been described in Escherichia coli where seven σ factors are involved in core RNA polymerase interactions and promoter recognition. Now, 7 years have passed since the completion of the first genome sequence of the opportunistic pathogen P. aeruginosa. Information from the genome of P. aeruginosa PAO1 identified 550 transcriptional regulators and 24 putative σ factors. Of the 24 σ, 19 were of extracytoplasmic function (ECF). Here, basic knowledge of σ and ECF proteins was reviewed with particular emphasis on their role in P. aeruginosa global gene regulation. Summarized data are obtained from in silico analysis of P. aeruginosaσ and ECF including rpoD (σ⁷⁰), RpoH (σ³²), RpoF (FliA or σ²⁸), RpoS (σS or σ³⁸), RpoN (NtrA, σ⁵⁴ or σN), ECF including AlgU (RpoE or σ²²), PvdS, SigX and a collection of uncharacterized σ ECF, some of which are implicated in iron transport. Coupled to systems biology, identification and functional genomics analysis of P. aeruginosaσ and ECF are expected to provide new means to prevent infection, new targets for antimicrobial therapy, as well as new insights into the infection process.