It is well known that biofilm-forming bacteria produce a large amount of extracellular polymeric substances, including exopolysaccharides (EPS), nucleic acids and proteins, and cause chronic or persistent infections. However, the genes associated with EPS production remain poorly understood. The aim of this study was to identify gene(s) responsible for EPS production in a clinically isolated Actinomyces oris (A. oris) strain K20, which has the ability to produce an abundance of EPS extracellularly. We performed random mutagenesis against A. oris strain K20, using EZ-Tn5^<TM> <KAN-2> Tnp Transposome^<TM> (EZ-Tn5). Screening by SEM identified five EPS production-deficient mutants from isolated transposants. The genes disrupted by the transposon insertion were determined by direct genome sequencing with the transposon-end primers and pyrosequencing. One of the mutants, designated the strain M154, had a transposon insertion within a gene that encodes polysaccharide deacetylase. We determined that the gene map around this gene revealed the existence of several open reading frames predicted to be associated with the biosynthesis of sugar and its transport. Our findings indicated this gene might be implicated in EPS production in A. oris strain K20.

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Our group recently determined the complete genome sequence of Rothia mucilaginosa strain DY-18, a clinical isolate from a persistent periapical periodontitis lesion. We bioinformatically determined that this strain possesses two sigma factors, one of which is a primary sigma factor that recognizes housekeeping promoters, and the other is an additional sigma factor whose promoter-binding activity may be regulated in response to physiolosical and environmental cues. Furthermore, the gene encoding the additional sigma factor is arranged in an operon-like structure with its cognate anti-sigma factor gene. Through multiple alignment analysis of the anti-sigma factor and its homologs, we found a conserved redox motif within these proteins. On the basis of these results, it was suggested that this sigma-antisigma regulatory system is a response to oxidative stress.

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