| Summary: | <p>Abstract</p> <p>Background</p> <p>Mutans streptococci are a group of gram-positive bacteria including the primary cariogenic dental pathogen <it>Streptococcus mutans </it>and closely related species. Two component systems (TCSs) composed of a signal sensing histidine kinase (HK) and a response regulator (RR) play key roles in pathogenicity, but have not been comparatively studied for these oral bacterial pathogens.</p> <p>Results</p> <p>HKs and RRs of 8 newly sequenced mutans streptococci strains, including <it>S. sobrinus </it>DSM20742, <it>S. ratti </it>DSM20564 and six <it>S. mutans </it>strains, were identified and compared to the TCSs of <it>S. mutans </it>UA159 and NN2025, two previously genome sequenced <it>S. mutans </it>strains. Ortholog analysis revealed 18 TCS clusters (HK-RR pairs), 2 orphan HKs and 2 orphan RRs, of which 8 TCS clusters were common to all 10 strains, 6 were absent in one or more strains, and the other 4 were exclusive to individual strains. Further classification of the predicted HKs and RRs revealed interesting aspects of their putative functions. While TCS complements were comparable within the six <it>S. mutans </it>strains, <it>S. sobrinus </it>DSM20742 lacked TCSs possibly involved in acid tolerance and fructan catabolism, and <it>S. ratti </it>DSM20564 possessed 3 unique TCSs but lacked the quorum-sensing related TCS (ComDE). Selected computational predictions were verified by PCR experiments.</p> <p>Conclusions</p> <p>Differences in the TCS repertoires of mutans streptococci strains, especially those of <it>S. sobrinus </it>and <it>S. ratti </it>in comparison to <it>S. mutans</it>, imply differences in their response mechanisms for survival in the dynamic oral environment. This genomic level study of TCSs should help in understanding the pathogenicity of these mutans streptococci strains.</p>
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