Expression of Streptococcus mutans fimA is iron-responsive and regulated by a DtxR homologue

Abstract

Iron uptake, transport and storage in Streptococcus mutans, the principal causative agent of human dental cavities, is unexplored despite early reports in the literature which predict a role for this trace metal in cariogenesis. Experiments in the authors' laboratory revealed several iron-responsive proteins in S. mutans, one of which reacted with a polyclonal antiserum directed against the FimA fimbrial adhesin from Streptococcus parasanguis on Western blots. The results of Western blot and Northern hybridization experiments support an inverse relationship between iron availability and S. mutans fimA expression, and metal ion uptake experiments implicate FimA in S. mutans 55 Fe transport. Cloning of the S. mutans fimA homologue facilitated the construction of a fimA knockout mutant which grew poorly in an ironlimiting medium relative to the wild-type progenitor strain, lending further support to a role for FimA in S. mutans iron transport. The authors also identified and cloned a dtxR-like gene (dlg) located downstream of fimA on the S. mutans chromosome, and noted increased fimA expression in a S. mutans dlg knockout mutant relative to wild-type on RNA spot blots and Western blots. The uptake of 55 Fe, which was also significantly increased in this mutant, was compromised in a fimA/dlg double knockout. These findings are consistent with a role for Dlg in the iron-mediated regulation of fimA, and possibly other S. mutans iron transporters. Finally, the cariogenic potential of the fimA and dlg knockout mutants was not significantly different from that of the wild-type progenitor in a germ-free rat model.

The src Homology 3-Like Domain of the Diphtheria Toxin Repressor (DtxR) Modulates Repressor Activation through Interaction with the Ancillary Metal Ion-Binding Site

“…Homologues of DtxR have been found in many pathogenic gram-positive microorganisms, including S. aureus (5), S. mutans (20), and T. pallidum (13). The closest relative to DtxR is IdeR from M. tuberculosis (19), and both metal ion-dependent repressors are believed to recognize similar operator sequences and to regulate similar regulons (8,11,19).…”

“…In the absence of these cations, apo-DtxR is inactive and unable to recognize its target operators. Homologues of DtxR have been identified in a number of microorganisms, including Staphylococcus aureus (5), Mycobacterium tuberculosis (19), Treponema pallidum (13), and Streptococcus mutans (20). Although different homologues display different cation selectivities, all members of this protein family appear to regulate genes responsible for transition metal cation homeostasis and virulence.…”

Involvement of Lsp, a Member of the LraI-Lipoprotein Family inStreptococcus pyogenes, in Eukaryotic Cell Adhesion and Internalization

“…This was initially observed in Synechocystis sp. where the MntC protein was found to transport Mn 2ϩ ions (1 (7,10,28,33,50). Mutants in the LraI genes did not only exhibit an increased requirement for certain divalent cations but also showed impairments in various biological functions such as spore formation, response to oxidative stress, and natural competence (reviewed by Jakubovics and Jenkinson [26]).…”

“…In several cases, an independently transcribed gene located up-or downstream of LraI operons was found to be involved in LraI operon expression (21,27,50). These genes usually encode negative regulators that are activated by increased concentrations of their cognate metal ion.…”

The Divergently Transcribed Streptococcus parasanguis Virulence-Associated fimA Operon Encoding an Mn 2+ -Responsive Metal Transporter and pepO Encoding a Zinc Metallopeptidase Are Not Coordinately Regulated

“…It has been suggested that the promoter domains of the fimA operon and pepO gene overlap and that the two may be coordinately regulated (14). Regulation of transcription is often the means by which metal ion acquisition is regulated (15,20,33). Classic examples of this are the ferric uptake repressor (Fur) of Escherichia coli and the diphtheria toxin repressor (DtxR) of Corynebacterium diphtheriae.…”