| Summary: | <p>Abstract</p> <p>Background</p> <p>LuxS may function as a metabolic enzyme or as the synthase of a quorum sensing signalling molecule, auto-inducer-2 (AI-2); hence, the mechanism underlying phenotypic changes upon <it>luxS </it>inactivation is not always clear. In <it>Helicobacter pylori</it>, we have recently shown that, rather than functioning in recycling methionine as in most bacteria, LuxS (along with newly-characterised MccA and MccB), synthesises cysteine via reverse transsulphuration. In this study, we investigated whether and how LuxS controls motility of <it>H. pylori</it>, specifically if it has its effects via <it>luxS</it>-required cysteine metabolism or via AI-2 synthesis only.</p> <p>Results</p> <p>We report that disruption of <it>luxS </it>renders <it>H. pylori </it>non-motile in soft agar and by microscopy, whereas disruption of <it>mccA</it><sub>Hp </sub>or <it>mccB</it><sub>Hp </sub>(other genes in the cysteine provision pathway) does not, implying that the lost phenotype is not due to disrupted cysteine provision. The motility defect of the Δ<it>luxS</it><sub>Hp </sub>mutant was complemented genetically by <it>luxS</it><sub>Hp </sub>and also by addition of <it>in vitro </it>synthesised AI-2 or 4, 5-dihydroxy-2, 3-pentanedione (DPD, the precursor of AI-2). In contrast, exogenously added cysteine could not restore motility to the Δ<it>luxS</it><sub>Hp </sub>mutant, confirming that AI-2 synthesis, but not the metabolic effect of LuxS was important. Microscopy showed reduced number and length of flagella in the Δ<it>luxS</it><sub>Hp </sub>mutant. Immunoblotting identified decreased levels of FlaA and FlgE but not FlaB in the Δ<it>luxS</it><sub>Hp </sub>mutant, and RT-PCR showed that the expression of <it>flaA, flgE</it>, <it>motA</it>, <it>motB</it>, <it>flhA </it>and <it>fliI </it>but not <it>flaB </it>was reduced. Addition of DPD but not cysteine to the Δ<it>luxS</it><sub>Hp </sub>mutant restored flagellar gene transcription, and the number and length of flagella.</p> <p>Conclusions</p> <p>Our data show that as well as being a metabolic enzyme, <it>H. pylori </it>LuxS has an alternative role in regulation of motility by modulating flagellar transcripts and flagellar biosynthesis through production of the signalling molecule AI-2.</p>
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