title: Transcriptional and Phenotypic Characterization of Novel Spx-Regulated Genes in Streptococcus mutans.
abstract: In oral biofilms, two of the major environmental challenges encountered by the dental pathogen Streptococcus mutans are acid and oxidative stresses. Previously, we showed that the S. mutans transcriptional regulators SpxA1 and SpxA2 (formerly SpxA and SpxB, respectively) are involved in stress survival by activating the expression of classic oxidative stress genes such as dpr, nox, sodA and tpx. We reasoned that some of the uncharacterized genes under SpxA1/A2 control are potentially involved in oxidative stress management. Therefore, the goal of this study was to use Spx-regulated genes as a tool to identify novel oxidative stress genes in S. mutans. Quantitative real-time PCR was used to evaluate the responses of ten Spx-regulated genes during H2O2 stress in the parent and Δspx strains. Transcription activation of the H2O2-induced genes (8 out of 10) was strongly dependent on SpxA1 and, to a lesser extent, SpxA2. In vitro transcription assays revealed that one or both Spx proteins directly regulate three of these genes. The gene encoding the FeoB ferrous permease was slightly repressed by H2O2 but constitutively induced in strains lacking SpxA1. Nine genes were selected for downstream mutational analysis but inactivation of smu127, encoding a subunit of the acetoin dehydrogenase was apparently lethal. In vitro and in vivo characterization of the viable mutants indicated that, in addition to the transcriptional activation of reducing and antioxidant pathways, Spx performs an important role in iron homeostasis by regulating the intracellular availability of free iron. In particular, inactivation of the genes encoding the Fe-S biogenesis SUF system and the previously characterized iron-binding protein Dpr resulted in impaired growth under different oxidative stress conditions, increased sensitivity to iron and lower infectivity in rats. These results serve as an entryway into the characterization of novel genes and pathways that allow S. mutans to cope with oxidative stress.
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America; Department of Physiological Sciences, Dentistry School of Piracicaba, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Lívia C C
authors.initials: LC
authors.lastname: Galvão
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: James H
authors.initials: JH
authors.lastname: Miller
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Jessica K
authors.initials: JK
authors.lastname: Kajfasz
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Kathy
authors.initials: K
authors.lastname: Scott-Anne
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America; Department of Physiological Sciences, Dentistry School of Piracicaba, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Irlan A
authors.initials: IA
authors.lastname: Freires
authors.affiliation: Department of General Biology, Laboratory of Physiology and Pathophysiology, State University of Ponta Grossa, Ponta Grossa, PR, Brazil.
authors.forename: Gilson C N
authors.initials: GC
authors.lastname: Franco
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America; Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: Jacqueline
authors.initials: J
authors.lastname: Abranches
authors.affiliation: Department of Physiological Sciences, Dentistry School of Piracicaba, State University of Campinas, Piracicaba, SP, Brazil.
authors.forename: Pedro L
authors.initials: PL
authors.lastname: Rosalen
authors.affiliation: Center for Oral Biology, University of Rochester Medical Center, Rochester, New York, United States of America; Department of Microbiology and Immunology, University of Rochester Medical Center, Rochester, New York, United States of America.
authors.forename: José A
authors.initials: JA
authors.lastname: Lemos
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D006861:Hydrogen Peroxide / Q000494:pharmacology; D009055:Mouth / Q000382:microbiology; D018384:Oxidative Stress; D051381:Rats; D013295:Streptococcus mutans / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D001426:Bacterial Proteins; D006861:Hydrogen Peroxide