The RNA chaperone Hfq has a role in the regulation of natural competence in Haemophilus influenzae
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Date
2010-06
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The Ohio State University
Abstract
Non-typeable Haemophilus influenzae (NTHi) is a Gram-negative commensal bacterium found in the upper respiratory tract of humans. NTHi is an opportunistic pathogen that causes otitis media, sinusitis and exacerbations of chronic obstructive pulmonary disease. This organism is naturally competent and can take up free DNA from the environment. The DNA taken up into the bacterium may be used as a source of nutrition, a substrate for DNA repair or for incorporation into the genome. Part of the competence regulon in H. influenzae is the pil operon, which encodes four genes whose products are required to make the type IV pilus (Tfp). This gene cluster is transcriptionally regulated in part by a protein designated Sxy; however, the mechanism by which sxy expression is regulated is unknown.
In many bacteria, small non-coding RNAs (sRNA) regulate gene expression by translational activation or repression of target mRNA sequences. These sRNAs function with the aid of Hfq, an RNA chaperone that binds both the sRNA and the sRNA’s mRNA target. We hypothesize that an sRNA acts as a post-transcriptional regulator of the pil operon in H. influenzae. To test this hypothesis we generated an hfq mutant in NTHi strain 86-028NP. In the absence of Hfq, transformation efficiency was reduced approximately 60%. These data suggest that Hfq, and by extension sRNAs, play a role in the natural competence of this organism. We then examined the expression levels of the PilA protein in 86-028NP and the hfq mutant by Western blot. The hfq mutant produced less PilA protein, compared to the parent strain.
However, there was no large difference in the transcript level for pilA in the hfq mutant when compared to the parent strain. The major difference in pil transcripts between the parent and the hfq mutant was with the transcript for pilC. These data suggest that in strain 86-028NP the loss of hfq affects expression of the pil operon post-transcriptionally, possibly via an sRNA. Also, a change in pilC expression in the hfq mutant may be affecting pilus biogenesis. Moreover, competence in strain 86-028NP, and by extension all Haemophilus spp., may be partially regulated by sRNAs.
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Keywords
RNA Hfq Haemophius influenzae, sRNA natural competence