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. 2011 Jul;320(2):110-7.
doi: 10.1111/j.1574-6968.2011.02293.x. Epub 2011 May 13.

Transcriptional repressor Rex is involved in regulation of oxidative stress response and biofilm formation by Streptococcus mutans

Jacob P Bitoun  1 , Anne H Nguyen, Yuwei Fan, Robert A Burne, Zezhang T Wen
Affiliations

Transcriptional repressor Rex is involved in regulation of oxidative stress response and biofilm formation by Streptococcus mutans

Jacob P Bitoun et al. FEMS Microbiol Lett. 2011 Jul.

Abstract

The transcriptional repressor Rex has been implicated in the regulation of energy metabolism and fermentative growth in response to redox potential. Streptococcus mutans, the primary causative agent of human dental caries, possesses a gene that encodes a protein with high similarity to members of the Rex family of proteins. In this study, we showed that Rex-deficiency compromised the ability of S. mutans to cope with oxidative stress and to form biofilms. The Rex-deficient mutant also accumulated less biofilm after 3 days than the wild-type strain, especially when grown in sucrose-containing medium, but produced more extracellular glucans than the parental strain. Rex-deficiency caused substantial alterations in gene transcription, including those involved in heterofermentative metabolism, NAD(+) regeneration and oxidative stress. Among the upregulated genes was gtfC, which encodes glucosyltransferase C, an enzyme primarily responsible for synthesis of water-insoluble glucans. These results reveal that Rex plays an important role in oxidative stress responses and biofilm formation by S. mutans.

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Figures

Figure 1
Figure 1
Growth study (A) and crystal violet staining of 24-hour biofilms (B). A: The impact of Rex-deficiency on growth rate was assessed using a Bioscreen C system with S. mutans strains growing on regular BHI broth with or without inclusion of methyl viologen (MV, 25 mM). Results show an extended lag phase for the Rex-deficient mutant and complementation of the mutant with a wild-type copy of rex plus its cognate promoter in multi-copy plasmid restored the phenotype. Data presented here are representatives of more than three independent experiments. B: Crystal violet staining of 24-hour biofilms was done on 96-well plates, and S. mutans UA159 and TW239 were grown on BM medium with glucose (G) and sucrose (S), respectively. Data represent average (±standard deviation) of more than three separate experiments.
Figure 2
Figure 2
SEM analysis of biofilms. S. mutans strains were grown on BM medium with glucose, sucrose or glucose plus sucrose as the supplemental carbohydrate sources and biofilms were allowed to accumulate on HA discs. Images show representatives of 24 hour biofilms of UA159 (UA) and TW239 (TW) grown on BM glucose (G) and BM sucrose (S), respectively, with the respective magnifications as indicated.
Figure 3
Figure 3
Analysis of glucan production. S. mutans biofilms were grown on HA discs in BM medium with glucose and sucrose as the supplemental carbohydrate sources. After 3-days, biofilms were treated with concanavalin A lectin conjugated with Alexa Fluor 488 and SYTO 59, and green fluorescent glucans and red fluorescent cell clusters were visualized using a confocal microscope at magnification of 600×. Data presented here are representative images of BM sucrose-grown UA159 (UA), TW239 (TW) and TW239C (TWC), respectively.
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