Gene Expression of Cold Shock and Other Stress-Related Genes in Vibrio vulnificus Grown in Pure Culture under Shellstock Temperature Control Conditions

Shellstock refrigeration after harvesting is recommended to prevent further increases in Vibrio vulnificus numbers in oysters, but it could potentially induce a cold shock response in this bacterium. V. vulnificus was incubated at 35, 25, 20, and 15 degree C and then subjected to 7.2 and 4 degree C for 1 week. A cold-adaptation response that enhanced cell culturability was observed when cells were incubated at 15 degree C prior to cold shock at 7.2 degree C. In vitro cold shock gene expression was analyzed by reverse transcriptase PCR (RT-PCR). The expression of cold shock genes csp1 and csp5 (homologous genes to cspA and cspV) remained constant, despite cold shock. However, the transcript of csp3 was constitutively expressed before and after cold shock, with a few exceptions. The synthesis of csp3 mRNA in V. vulnificus C7184Tr (an avirulent strain) was induced only after 15 degree C incubation and cold shock at 4 degree C. The expression of csp4 was repressed after cold shock. Our data showed that the csp sub(s) tested in this study are not cold inducible. The transcripts of two oxidative stress-related genes, oxyR and katG, showed different induction patterns among strains after cold shock, suggesting that V. vulnificus cells encountered oxidative stress during cold shock.