D-103. Involvement of thrB in Antoinducer-2 Production in Streptococcus sanguinis

X. Ge, P. Xu;
Virginia Commonwealth Univ., Richmond, VA.

Background: Autoinducer-2 (AI-2) is one of the important signal molecules for quorum-sensing in both gram-negative and gram-positive bacteria. AI-2 is implicated in bacterial communication, biofilm formation, virulence and stress response. The luxS gene has been demonstrated involvement in AI-2 biosynthesis in bacteria including many streptococci. AI-2 is a byproduct of the activated methyl cycle (AMC). ThrB, a putative homoserine kinase required for threonine biosynthesis, was identified as one of virulence factors of Streptococcus sanguinis in rabbit endocarditis model. We found that the thrB mutant produced less AI-2 in luminescent assay via Vibrio harveyi reporter. The purpose of this study is to investigate the role of thrB gene in S. sanguinis AI-2 production. Methods: luxS, thrB and other related genes in threonine or methionine biosynthesis in S. sanguinis SK36 were mutated and complemented by PCR recombinant mutagenesis. AI-2 production bioassay was performed using V. harveyi BB170 for the luxS and thrB mutants. Results: AI-2 production increased with cells increase at exponential growth stage in S. sanguinis SK36. Compare to parent strain SK36, AI-2 production was inhibited in luxS-deficient mutant and significantly attenuated in thrB-deficient mutant. However, mutation of thrA and thrC, two other genes necessary for threonine biosynthesis, did not affect the AI-2 production. Mutation of metA and metB, connected methionine pathway and homoserine-threonine pathway, had no effect on AI-2 production. Moreover, addition of the intermediates in homoserine-methionine pathways did not alter the reduction in AI-2 production in thrB-deficient mutant. Conclusion: The results suggest thrB is implicated in AI-2 production in S. sanguinis. The influence of thrB on AI-2 production may not result from impacting homoserine-methionine metabolic pathways.