Analyzing Possible Native Functions of the Quinolone Resistance Gene in Vibrio vulnificus.

The worldwide distribution of genes found on plasmids and their presence on the chromosomes of aquatic bacteria, such as , one of the suspected sources, suggests an origin before the development of synthetic quinolones. However, their native function remains unknown. Previous work indicated that expression of in was induced by cold shock. To investigate its role further, we constructed single in-frame deletion mutants in and (the gene for cold shock protein) and a double mutant in and in ATCC 17562 to evaluate the response to different environmental conditions and stresses and to exposure to various DNA-damaging agents. We found that is involved in resistance to ciprofloxacin, levofloxacin, and mitomycin C and in the cold shock response in Moreover, Δ and Δ mutants showed slower growth when they were treated with bile salts at 37°C and then shifted to 15°C (cold shock) without bile salts in the medium, with the effect being stronger in the double mutant. This transition may mimic what happens when is ingested into the gastrointestinal tract and released in its natural environment. Cold shock and bile salts induced the expression of and DNA gyrase and topoisomerase IV genes. However, no induction was found in the Δ mutant, suggesting that the gene is involved in the response to DNA damage and nucleic acid secondary structure.