Differential expression of vvhA and CPS operon allele 1 genes in Vibrio vulnificus under biofilm and planktonic conditions

Abstract

Examination of genes encoding for the virulence factors, hemolysin/cytolysin (vvhA) and capsular polysaccharide (CPS allele 1), during biofilm formation revealed that their expression was influenced by the maturity of the biofilm as well as by temperature. At 24 °C, expression of vvhA during biofilm formation was low between 4 and 12 h but increased 10-fold by 24 h to (5.1 × 10⁴ ± 6.3 × 10³mRNA copies/ml) as the biofilm matured. Compared to planktonic cells, expression of vvhA during biofilm formation at 24 °C was initially up-regulated at 4 h (1.07 ± 0.00-fold) but then was down-regulated almost four-fold during the intermediate and mature stages of biofilm formation. In contrast, vvhA expression at 37 °C was up-regulated almost four-fold in the early stages (4 and 6 h) of biofilm formation and remained two-fold up-regulated by 24 h even as the biofilm was deteriorating. CPS allele 1 expression at 24 °C during biofilm formation was up-regulated (1.50 ± 0.18-fold) during the initial attachment phase of the cells but was strongly down-regulated during the intermediate phases at 8 and 10 h (74.42 ± 42.16-fold and 453.76 ± 193.32-fold, respectively), indicating that capsular polysaccharide (CPS) is not important to intermediate biofilm architecture. Interestingly, as the biofilm matured by 24 h, expression of CPS allele 1 was again up-regulated (1.88 ± 1.07), showing that CPS plays a role in mature biofilm. At 37 °C, CPS allele 1 expression was significantly up-regulated (up to 10⁵) during biofilm formation, indicating that the biofilm form of V. vulnificus may be preferred over the planktonic form in the human host.