Autoinducer-2 regulated genes in Streptococcus mutans UA159 and global metabolic effect of the luxS mutation

Helmholtz-Center for Infection Research, Division of Cell Biology, Braunschweig, Germany; Technical University of Braunschweig, Institute of Ecological Chemistry, Braunschweig, Germany; University of Toronto, Dental Research Institute, Toronto, Canada

^* To whom correspondence should be addressed. Email: iwd{at}helmholtz-hzi.de.

	Abstract

Autoinducer-2 (AI-2) is the only species-nonspecific autoinducer known in bacteria and is produced by both Gram-negative and Gram-positive organisms. Consequently, it is proposed to function as a universal quorum-sensing signal for interaction between bacterial species. AI-2 is produced as the byproduct of a metabolic transformation carried out by the LuxS enzyme. To separate the metabolic function of the LuxS enzyme from the signalling role of AI-2, we carried out a global transcriptome analysis of a luxS null mutant culture of Streptococcus mutans UA159, an important cariogenic bacterium and crucial component of the dental plaque biofilm community, in comparison to a luxS null mutant culture supplemented with chemically pure 4,5-dihydroxy-2,3-pentanedione (DPD), the precursor of AI-2. The data revealed fundamental changes in gene expression affecting 585 genes (30 % of the genome) which could not be restored by the signal molecule AI-2 and are therefore not caused by quorum sensing but by lack of the transformation carried out by the LuxS enzyme in the activated methyl cycle. All functional classes of enzymes were affected, including genes known to be important for biofilm formation, bacteriocin synthesis, competence and acid tolerance. At the same time, 59 genes were identified whose transcription clearly responded to the addition of AI-2. Some of them were related to protein synthesis, stress, and cell division. Three membrane transport proteins were upregulated which are not related to any of the known AI-2 transporters. Three transcription factors were identified whose transcription was stimulated repeatedly by AI-2 addition during growth. Finally, a global regulatory protein, the subunit of the RNA polymerase (rpoE) was induced 147 fold by AI-2, representing the largest differential gene expression observed. The data show that many phenotypes related to the luxS mutation can not be ascribed to quorum sensing and identified for the first time regulatory proteins potentially mediating AI-2 based signalling in Gram-positive bacteria.