SloR modulation of the Streptococcus mutans acid tolerance response involves the GcrR response regulator as an essential intermediary.
Streptococcus mutans, the primary causative agent of human dental caries, grows as a biofilm on the tooth surface, where it metabolizes dietary carbohydrates and generates acid byproducts that demineralize tooth enamel. A drop in plaque pH stimulates an adaptive acid-tolerance response (ATR) in this oral pathogen that allows it to survive acid challenge at pHs as low as 3.0. In the present study, we describe the growth of an S. mutans mutant, GMS901, that harbours an insertion-deletion mutation in gcrR, a gene that encodes a transcriptional regulatory protein. The mutant is acid-sensitive and significantly compromised in its ATR relative to the UA159 wild-type progenitor strain. Consistent with these findings are the results of real-time quantitative RT-PCR (qRT-PCR) experiments that support the GcrR-regulated expression of known ATR genes, including atpA/E and ffh. Although we observed gcrR transcription that was not responsive to acidic pH, we did note a significant increase in gcrR expression when S. mutans cells were grown in a manganese-restricted medium. Interestingly, the results of gel mobility shift assays indicate that the S. mutans SloR metalloregulatory protein is a potential regulator of gcrR by virtue of its manganese-dependent binding to the gcrR promoter region, and expression studies support the hypothesis that sloR transcription is responsive to manganese deprivation and acidic pH. Taking these results together, we propose that SloR-Mn modulates S. mutans gcrR expression as part of a general stress response, and that GcrR acts downstream of SloR to control the ATR.
Dunning
Daniel W
DW
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
McCall
Lathan W
LW
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
Powell
William F
WF
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
Arscott
W Tristram
WT
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
McConocha
Erin M
EM
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
McClurg
Cheryl J
CJ
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
Goodman
Steven D
SD
Division of Diagnostic Sciences, University of Southern California School of Dentistry, Los Angeles, CA 90089, USA.
Spatafora
Grace A
GA
Department of Biology, Middlebury College, 276 Bicentennial Way, MBH354, Middlebury, VT 05753, USA.
D000143:Acids / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D004269:DNA, Bacterial / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D020869:Gene Expression Profiling; D023061:Gene Order; D006801:Humans; D054643:INDEL Mutation; D008345:Manganese / Q000378:metabolism; D050296:Microbial Viability; D011485:Protein Binding; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013295:Streptococcus mutans / Q000187:drug effects / Q000502:physiology*; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
D000143:Acids; D001426:Bacterial Proteins; D004269:DNA, Bacterial; D014157:Transcription Factors; D008345:Manganese