Characterization of fliYfunction and regulation in the squid-vibrio symbiosis
The Hawaiian bobtail squid, Euprymna scolopes, forms a symbiosis with the marine bacterium, Vibrio fischeri, in a specialized structure called the light organ. Bacterial transmission in the squid-vibrio symbiosis is horizontal, i.e., juvenile squid hatch from their eggs un-colonized and acquire V. fischeri symbionts from the surrounding seawater. Previous work demonstrated that cysteine auxotrophs of V. fischeri are accommodated within the light organ; however, free cysteine was not detected in the light organ matrix fluid. An alternative mechanism V. fischeri can use to acquire cysteine involves the periplasmic binding protein, FliY, which binds to cystine, the oxidized form of cysteine. Therefore, we hypothesized that FliY allows for the acquisition of host-derived cystine within the light organ. However, a colonization defect was not observed with a ∆fliY mutant, suggesting our initial hypothesis is incorrect. In this study, we also found that the expression of fliY varies among the different populations within the light organ. Culture work has shown that fliY expression is repressed by cysteine and cystine. The results of a transposon mutagenesis screen have suggested that the cysteine biosynthetic pathway activates fliY expression. A regulator of this biosynthetic pathway is the protein CysB. Taken together, our results suggest that some V. fischeri populations within the squid light organ must synthesize cysteine while others receive cysteine in a form different from free cysteine or cystine.
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|Work Title||Characterization of fliYfunction and regulation in the squid-vibrio symbiosis|
|License||Attribution-NonCommercial-NoDerivs 3.0 United States|
|Publication Date||Spring 2015|
|Deposited||June 22, 2016|
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