Capsule expression regulated by a two-component signal transduction system inStreptococcus iniae

Abstract

Streptococcus iniae causes disease in fish and humans and the presence of capsule is associated with virulence. Tn917 transposon mutagenesis was performed to identify capsule-associated genes and a mutant was isolated, with an insertion in a genetic locus encoding a two-component signal transduction system (TCS), which we termed sivS/R. sivS and sivR encode a 506-amino-acid (aa) putative histidine kinase and a 223-aa putative response regulator, respectively. In order to investigate the role of sivS/R, a deletion-insertion mutant was constructed using a PCR ligation technique. Real-time PCR showed that transcription of cpsA, the first gene in the S. iniae capsule operon, was reduced in the mutant, indicating that sivS/R regulates expression of this gene at the transcriptional level. Whole human blood killing assays demonstrated that unlike the parent, the mutant was susceptible to phagocytosis. Transmission electron microscopy showed exopolysaccharide on the surface of the parent strain but not the mutant which showed aberrant asymmetric septae that resulted in clumps of abnormal-shaped cells. Exponential growth rates of the mutant and parent strain were similar, although the mutant exhibited a longer lag phase. We conclude that sivS/R regulates capsule expression, thus affecting the ability to evade phagocytosis.

Innate Immune Response to Streptococcus iniae Infection in Zebrafish Larvae

“…The polysaccharide capsule is an important virulence factor for S. iniae in establishing systemic disease in fish (36,(41)(42)(43)57). We next sought to determine whether the S. iniae 9117 capsule mutant iniae or an equivalent of 1,000 CFU wild-type bacteria heat killed at 95°C for 1 h (n ϭ 24 per group).…”

Towards Control ofStreptococcus iniae

“…In a flounder isolate obtained in Japan, insertions in cpsH , cpsM , cpsI , and orf276 of strain NUF631 resulted in attenuation, which was measured by increased chemiluminescence response of macrophages and loss of acidic polysaccharides ( 26 ). Like CAMP factor and streptolysin S, the 2-component system sivS/R is involved in transcriptional regulation of the capsular operon ( 32 ). …”

Novel Exopolysaccharides Produced byLactococcus lactissubsp.lactis, and the Diversity ofepsEGenes in the Exopolysaccharide Biosynthesis Gene Clusters

“…For example, an eps mutant of Streptococcus iniae is susceptible to phagocytosis whereas its parent strain is not. 44) Furthermore, the mitogenic activity of an acidic polysaccharide from Lactobacillus delbrueckii subsp. bulgaricus was completely abolished by dephosphorylation.…”