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.
