title: Sharply Tuned pH Response of Genetic Competence Regulation in Streptococcus mutans: a Microfluidic Study of the Environmental Sensitivity of comX.
abstract: Genetic competence in Streptococcus mutans is a transient state that is regulated in response to multiple environmental inputs. These include extracellular pH and the concentrations of two secreted peptides, designated CSP (competence-stimulating peptide) and XIP (comX-inducing peptide). The role of environmental cues in regulating competence can be difficult to disentangle from the effects of the organism's physiological state and its chemical modification of its environment. We used microfluidics to control the extracellular environment and study the activation of the key competence gene comX. We find that the comX promoter (PcomX) responds to XIP or CSP only when the extracellular pH lies within a narrow window, about 1 pH unit wide, near pH 7. Within this pH range, CSP elicits a strong PcomX response from a subpopulation of cells, whereas outside this range the proportion of cells expressing comX declines sharply. Likewise, PcomX is most sensitive to XIP only within a narrow pH window. While previous work suggested that comX may become refractory to CSP or XIP stimulus as cells exit early exponential phase, our microfluidic data show that extracellular pH dominates in determining sensitivity to XIP and CSP. The data are most consistent with an effect of pH on the ComR/ComS system, which has direct control over transcription of comX in S. mutans.
authors.affiliation: Department of Physics, University of Florida, Gainesville, Florida, USA.
authors.forename: Minjun
authors.initials: M
authors.lastname: Son
authors.affiliation: Department of Physics, University of Florida, Gainesville, Florida, USA.
authors.forename: Delaram
authors.initials: D
authors.lastname: Ghoreishi
authors.affiliation: Department of Oral Biology, University of Florida, Gainesville, Florida, USA.
authors.forename: Sang-Joon
authors.initials: SJ
authors.lastname: Ahn
authors.affiliation: Department of Oral Biology, University of Florida, Gainesville, Florida, USA.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Burne
authors.affiliation: Department of Physics, University of Florida, Gainesville, Florida, USA sjhagen@ufl.edu.
authors.forename: Stephen J
authors.identifier: http://orcid.org/0000-0002-3373-5033
authors.initials: SJ
authors.lastname: Hagen
mesh_terms: D001426:Bacterial Proteins / Q000096:biosynthesis*; D001431:Bacteriological Techniques; D061269:DNA Transformation Competence / Q000187:drug effects*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects*; D006863:Hydrogen-Ion Concentration; D044085:Microfluidics; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D013295:Streptococcus mutans / Q000187:drug effects* / Q000235:genetics*; D014157:Transcription Factors / Q000096:biosynthesis*
chemical_list: D001426:Bacterial Proteins; C120829:ComX protein, Streptococcus; D014157:Transcription Factors