Abstract
The Rex repressor has been implicated in regulation of central carbon and energy metabolism in Gram-positive bacteria. We have previously shown that Streptococcus mutans, the primary causative agent of dental caries, alters its transcriptome upon Rex-deficiency and renders S. mutans to have increased susceptibility to oxidative stress, aberrations in glucan production, and poor biofilm formation. In this study, we showed that rex in S. mutans is co-transcribed as an operon with downstream guaA, encoding a putative glutamine amidotransferase. Electrophoretic mobility shift assays showed that recombinant Rex bound promoters of target genes avidly and specifically, including those down-regulated in response to Rex-deficiency, and that the ability of recombinant Rex to bind to selected promoters was modulated by NADH and NAD+. Results suggest that Rex in S. mutans can function as an activator in response to intracellular NADH/NAD+ level, although the exact binding site for activator Rex remains unclear. Consistent with a role in oxidative stress tolerance, hydrogen peroxide challenge assays showed that the Rex-deficient mutant, TW239, and the Rex/GuaA double mutant, JB314, were more susceptible to hydrogen peroxide killing than the wildtype, UA159. Relative to UA159, JB314 displayed major defects in biofilm formation, with a decrease of more than 50-fold in biomass after 48-hours. Collectively, these results further suggest that Rex in S. mutans regulates fermentation pathways, oxidative stress tolerance, and biofilm formation in response to intracellular NADH/NAD+ level. Current effort is being directed to further investigation of the role of GuaA in S. mutans cellular physiology.
Highlights
Streptococcus mutans, the major causative agent of human dental caries, lives almost exclusively as tenacious biofilms on the tooth surface in an environment featured with fluctuating and often unpredictable conditions in nutrient availability, pH, temperature, oxygen tension, saliva, and shearing force [1,2]
We showed that deficiency of Rex in S. mutans causes substantial alterations in the transcriptional profile and the abilities of the deficient mutant to survive oxidative stress and form biofilms [25]
We provided further evidences that similar to B. subtilis and S. aureus, Rex in S. mutans binds to target promoters and its binding efficiency is affected by the level of NADH:NAD+
Summary
Streptococcus mutans, the major causative agent of human dental caries, lives almost exclusively as tenacious biofilms on the tooth surface in an environment featured with fluctuating and often unpredictable conditions in nutrient availability, pH, temperature, oxygen tension, saliva, and shearing force [1,2]. When glucose is available in excess or during aerobic growth, S. mutans catabolizes glucose through homofermentation pathways, yielding primarily lactate. During growth under glucose limiting or anaerobic conditions, S. mutans undergoes heterofermentation, generating formate, acetate, acetoin, and ethanol. Despite the abundance of oxygen in the oral cavity, plaque biofilms support growth of a wide range of bacteria, including facultative and obligate anaerobes. Plaque bacteria, including anaerobes, have developed active defense mechanisms against oxygen and oxidative stress [10]. In S. mutans, oxygen and the deleterious reactive oxygen species (ROS) are scavenged through an array of cytoprotective enzymes, including alkylhydroperoxide reductases (AhpCF), glutathione reductase (GshR), superoxide dismutase (SodA), thioredoxin reductase (TrxA), and NADH oxidase (Nox) [11,13,14,15]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
