Reduced virulence of a hfq mutant of Pseudomonas aeruginosa O1

Abstract The Sm-like protein Hfq has been implicated in the regulation of σ S -dependent and σ S -independent genes in E. coli and in the regulation of virulence factors in both, Yersinia enterocolitica and Brucella abortus . Here, we have studied the effect of Hfq on virulence and stress response of Pseudomonas aeruginosa (PAO1). We have constructed a PAO1 hfq − mutant and a PAO1 hfq-rpoS − double mutant to permit distinction between direct and indirect effects of Hfq. When compared to the wild-type and the rpoS − strains, the hfq knock out strain showed a reduced growth rate and was unable to utilize glucose as a sole carbon source. Elastase activity was 80% reduced in the hfq − mutant when compared to the wild-type or the rpoS − strain, whereas alginate production seemed to be solely affected by σ S . The production of catalase and pyocyanin was shown to be affected in an additive manner by both, Hfq and σ S . Moreover, twitching and swarming mediated by typeIV pili was shown to be impaired in the hfq − mutant. When compared to PAO1 wild-type and the rpoS − mutant, the hfq − mutant decreased virulence in Galleria mellonella by a factor of 1×10 4 and 5×10 3 , respectively. Likewise, when compared to wild-type, the PAO1 hfq − mutant was significantly attenuated in virulence when administered intraperitoneally in mice. These results strongly suggest that Hfq is a global regulator of PAO1 virulence and stress response which is not exclusively due to its role in stimulating the synthesis of σ S .