Role of Streptococcus mutans eukaryotic-type serine/threonine protein kinase in interspecies interactions with Streptococcus sanguinis

Objective: Interspecies interactions of oral streptococci involve the production and excretion of antimicrobial compounds to compete successfully during colonization. Bacteriocin production by Streptococcus mutans and hydrogenperoxide (H₂O₂) production by Streptococcus sanguinis have been demonstrated as crucial for the clinical relevant antagonism between both species. A potential target of H₂O₂ is the cell-envelop of S. mutans. In the present study, the role of cell-envelop associated eukaryotic serine/threonine protein kinase (STPK) in S. mutans during interspecies competition has been investigated. Design: Allelic replacement via homologous recombination of the STPK encoding gene with a kanamycin resistant determinant has been constructed. The mutant has been screened for the susceptibility towards cell-envelope stress. A previously developed spotting assay was used to simulate interspecies competition. Results: The STPK^- mutant showed an increased susceptibility towards envelop stress caused by H₂O₂ and was significantly more inhibited during interspecies competition assays. Conclusions: S. mutans is able to sense antimicrobial compounds excreted by competing species and can potentially adjust the cell-envelop towards an increased resistance.