Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>
Pyruvate oxidase (SpxB)-dependent H
<jats:sub>2</jats:sub>
O
<jats:sub>2</jats:sub>
production is under the control of carbon catabolite protein A (CcpA) in the oral species
<jats:named-content content-type="genus-species">Streptococcus sanguinis</jats:named-content>
and
<jats:named-content content-type="genus-species">Streptococcus gordonii</jats:named-content>
. Interestingly, both species react differently to the presence of the preferred carbohydrate source glucose.
<jats:named-content content-type="genus-species">S. gordonii</jats:named-content>
CcpA-dependent regulation of
<jats:italic>spxB</jats:italic>
follows classical carbon catabolite repression. Conversely,
<jats:italic>spxB</jats:italic>
expression in
<jats:named-content content-type="genus-species">S. sanguinis</jats:named-content>
is not influenced by glucose but is repressed by CcpA. Here, we constructed strains expressing the heterologous versions of CcpA or the
<jats:italic>spxB</jats:italic>
promoter region to learn if the distinct regulation of
<jats:italic>spxB</jats:italic>
expression is transferable from
<jats:named-content content-type="genus-species">S. gordonii</jats:named-content>
to
<jats:named-content content-type="genus-species">S. sanguinis</jats:named-content>
and vice versa. While cross-species binding of CcpA to the
<jats:italic>spxB</jats:italic>
promoter is conserved
<jats:italic>in vitro</jats:italic>
, we were unable to swap the species-specific regulation. This suggests that a regulatory mechanism upstream of CcpA most likely is responsible for the observed difference in
<jats:italic>spxB</jats:italic>
expression. Moreover, the overall ecological significance of differential
<jats:italic>spxB</jats:italic>
regulation in the presence of various glucose concentrations was tested with additional oral streptococcus isolates and demonstrated that carbohydrate-dependent and carbohydrate-independent mechanisms exist to control expression of
<jats:italic>spxB</jats:italic>
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.
</jats:p>
<jats:p>
<jats:bold>IMPORTANCE</jats:bold>
Polymicrobial diseases are the result of interactions among the residential microbes, which can lead to a dysbiotic community.
<jats:named-content content-type="genus-species">Streptococcus sanguinis</jats:named-content>
and
<jats:named-content content-type="genus-species">Streptococcus gordonii</jats:named-content>
are considered commensal species that are present in the healthy dental biofilm. Both species are able to produce significant amounts of H
<jats:sub>2</jats:sub>
O
<jats:sub>2</jats:sub>
via the enzymatic action of the pyruvate oxidase SpxB. H
<jats:sub>2</jats:sub>
O
<jats:sub>2</jats:sub>
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. Detailed knowledge of the regulatory mechanisms will aid in a better understanding of oral disease development and how to prevent dysbiosis.
</jats:p>