Effect of Type Three Secretion System and Phospholipases on Virulence of Harveyi Clade Vibrios ( Vibrio harveyi and Vibrio campbellii)

Abstract

Vibrios belonging to Harveyi clade ( V. harveyi and V. campbellii) are pathogenic marine bacteria in shrimp causing devastating vibriosis in aquaculture industry. Several virulence factors are involved in the virulence including type three secretion system (TTSS) and phospholipases. The TTSS are specialized secretion apparatus used by pathogens to inject virulence factors directly into host cells. To facilitate the invasion of host tissues, microbial cells possess constitutive and inducible hydrolytic enzymes such as phospholipases. But there is a knowledge gap on expression of virulence genes and it's relation to the virulence. Therefore this study aimed at detecting the connection between the expression of virulence factors and the virulence of Harveyi clade vibrios. The level of expression of genes o f type three secretion system such as, vopD (gene for outer protein), vcrD (gene for calcium response protein), vscP (gene for secretion protein) and five genes responsible for phospholipase activity [pll, pl2, pl3: phospholiphase genes; omplAl, omplA2: outer membrane phospholiphase A genes) were quantified. Genes of type three secretion system (TTSS) showed clear differences in expression levels between virulent and avirulent strains with significantly high expression in avirulent isolates (Fold-expression 27.4,19.7 and 13.4 for vopD, vcrD and vcsP respectively) and lower in virulent isolates (Fold-expression 1 for all three genes). Two out of the five phospholipases genes showed significant differences between the different strains having relatively higher expression in low virulence strains and having relatively low expression in high virulence strains. The TTSS genes and some of the phospholipases genes expression is inversely proportionate to the virulence. Findings of this research can have significant consequences on the implementation of control measures for the devastating luminescent Vibriosis problem in the aquaculture industry.