title: Deficiency of BrpB causes major defects in cell division, stress responses and biofilm formation by Streptococcus mutans.
abstract: Streptococcus mutans, the primary aetiological agent of dental caries, possesses an YjeE-like protein that is encoded by locus SMU.409, herein designated brpB. In this study, a BrpB-deficient mutant, JB409, and a double mutant deficient of BrpB and BrpA (a paralogue of the LytR-CpsA-Psr family of cell wall-associated proteins), JB819, were constructed and characterized using function assays and microscopy analysis. Both JB409 and JB819 displayed extended lag phases and drastically slowed growth rates during growth in brain heart infusion medium as compared to the wild-type, UA159. Relative to UA159, JB409 and JB819 were more than 60- and 10-fold more susceptible to acid killing at pH 2.8, and more than 1 and 2 logs more susceptible to hydrogen peroxide, respectively. Complementation of the deficient mutants with a wild-type copy of the respective gene(s) partly restored the acid and oxidative stress responses to a level similar to the wild-type. As compared to UA159, biofilm formation by JB409 and JB819 was drastically reduced (P<0.001), especially during growth in medium containing sucrose. Under a scanning electron microscope, JB409 had significantly more giant cells with an elongated, rod-like morphology, and JB819 formed marble-like super cells with apparent defects in cell division. As revealed by transmission electron microscopy analysis, BrpB deficiency in both JB409 and JB819 resulted in the development of low electron density patches and formation of a loose nucleoid structure. Taken together, these results suggest that BrpB likely functions together with BrpA in regulating cell envelope biogenesis/homeostasis in Strep. mutans. Further studies are under way to elucidate the mechanism that underlies the BrpA- and BrpB-mediated regulation.
authors.affiliation: Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, LA 70119, USA.
authors.forename: Jacob P
authors.initials: JP
authors.lastname: Bitoun
authors.affiliation: Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, LA 70119, USA.
authors.forename: Sumei
authors.initials: S
authors.lastname: Liao
authors.affiliation: Biology and Bioinformatics, Los Alamos National Laboratory, NM 87545, USA.
authors.forename: Gary G
authors.initials: GG
authors.lastname: Xie
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St Louis, MO 63110 USA.
authors.forename: Wandy L
authors.initials: WL
authors.lastname: Beatty
authors.affiliation: Department of Microbiology, Immunology and Parasitology, School of Medicine, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA.|Department of Comprehensive Dentistry and Biomaterials, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, LA 70119, USA.|Center of Excellence in Oral and Craniofacial Biology, School of Dentistry, Louisiana State University Health Sciences Center, New Orleans, LA 70119, USA.
authors.forename: Zezhang T
authors.initials: ZT
authors.lastname: Wen
mesh_terms: D000143:Acids / Q000633:toxicity; D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D018441:Biofilms / Q000254:growth & development*; D002455:Cell Division; D003470:Culture Media / Q000737:chemistry; D015964:Gene Expression Regulation, Bacterial; D055786:Gene Knockout Techniques; D005816:Genetic Complementation Test; D006861:Hydrogen Peroxide / Q000633:toxicity; D006863:Hydrogen-Ion Concentration; D050296:Microbial Viability / Q000187:drug effects; D008855:Microscopy, Electron, Scanning; D046529:Microscopy, Electron, Transmission; D013295:Streptococcus mutans / Q000187:drug effects / Q000235:genetics / Q000502:physiology* / Q000648:ultrastructure*; D013312:Stress, Physiological
chemical_list: D000143:Acids; D001426:Bacterial Proteins; D003470:Culture Media; D006861:Hydrogen Peroxide