Expression of Streptococcus mutans fimA is iron-responsive and regulated by a DtxR homologue.
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 iron-limiting 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.
Spatafora
Grace
G
Department of Biology, Middlebury College, Middlebury, VT 05753, USA1.
Moore
Meagan
M
Department of Biology, Middlebury College, Middlebury, VT 05753, USA1.
Landgren
Susan
S
Department of Biology, Middlebury College, Middlebury, VT 05753, USA1.
Stonehouse
Emily
E
Department of Biology, Middlebury College, Middlebury, VT 05753, USA1.
Michalek
Suzanne
S
Department of Microbiology, The University of Alabama at Birmingham, Birmingham, AL 35294, USA2.
D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D001693:Biological Transport, Active; D015152:Blotting, Northern; D015153:Blotting, Western; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D036781:Fimbriae Proteins; D015964:Gene Expression Regulation, Bacterial; D007501:Iron / Q000378:metabolism*; D012333:RNA, Messenger / Q000032:analysis; D013295:Streptococcus mutans / Q000235:genetics* / Q000378:metabolism
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; C075586:DtxR protein, Corynebacterium diphtheriae; D012333:RNA, Messenger; C063055:fimbrillin; D036781:Fimbriae Proteins; D007501:Iron