3 years ago

Distinct Regulatory Role of Carbon Catabolite Protein A (CcpA) in Oral Streptococcal spxB Expression.

Nyssa Cullin, Rodrigo A Giacaman, Revathi Masilamani, Sylvio Redanz, Jens Kreth, Justin Merritt
Pyruvate oxidase (SpxB) dependent H2O2 production is under the control of carbon catabolite protein A (CcpA) in the oral species Streptococcus sanguinis and Streptococcus gordonii Interestingly, both species react differently to the presence of the preferred carbohydrate source glucose. S. gordonii CcpA dependent regulation of spxB follows classical carbon catabolite repression. Conversely, spxB expression in S. sanguinis is not influenced by glucose, but is repressed by CcpA. Here we constructed strains expressing the heterologous versions of CcpA or the spxB promoter region to learn if the distinct regulation of spxB expression is transferable from S. gordonii to S. sanguinis and vice versa While cross species binding of CcpA to the spxB promoter is conserved in vitro, we were unable to swap the species-specific regulation. This suggests that a regulatory mechanism upstream of CcpA is most-likely responsible for the observed difference in spxB expression. Moreover, the overall ecological significance of differential spxB regulation in the presence of varying glucose concentrations is tested with additional oral streptococci isolates and demonstrates that carbohydrate dependent and carbohydrate independent mechanisms exist to control expression of spxB in the oral biofilm. Overall, our data demonstrate the unexpected finding that metabolic pathways between two closely related oral streptococcal species can be regulated differently despite an exceptionally high DNA sequence identity.Importance Polymicrobial diseases are the result of interactions among the residential microbes, which lead to a dysbiotic community. Streptococcus sanguinis and Streptococcus gordonii are considered commensal species that are present in the healthy dental biofilm. Both species are able to produce significant amounts of H2O2 via the enzymatic action of the pyruvate oxidase, SpxB. H2O2 is able to inhibit species associated with oral diseases SpxB and its gene regulatory elements present in both species are highly conserved. Nonetheless, a differential response to the presence of glucose was observed. Here we investigate the mechanisms that lead to this differential response. A detailed knowledge of the regulatory mechanisms will aid in a better understanding of oral disease development and how to prevent dysbiosis.

Publisher URL: http://doi.org/10.1128/JB.00619-17

DOI: 10.1128/JB.00619-17

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