Regulatory Involvement of the PerR and SloR Metalloregulators in the Streptococcus mutans Oxidative Stress Response

Abstract

Streptococcus mutans is a commensal of the human oral microbiome that can promote dental caries under conditions of dysbiosis. This study investigates metalloregulators and their involvement in the S. mutans oxidative stress response. Oxidative stress in the human mouth can derive from temporal increases in reactive oxygen species (ROS) after meal consumption and from endogenous bacterial ROS-producers that colonize the dentition. We hypothesize that the S. mutans PerR (SMU.593) and SloR (SMU.186) metalloregulatory proteins contribute to the regulation of oxidative stress genes and their products. Expression assays with S. mutans UA159 wild type cultures exposed to H2O2 reveal that H2O2 upregulates perR, and that PerR represses sloR transcription upon binding directly to Fur and PerR consensus sequences within the sloR operator. In addition, the results of Western blot experiments implicate the Clp proteolytic system in SloR degradation under conditions of H2O2-stress. To reveal a potential role for SloR in the H2O2-resistant phenotype of S. mutans GMS802 (a perR-deficient strain), we generated a sloR/perR double knockout mutant, GMS1386, where we observed upregulation of the tpx and dpr antioxidant genes. These results are consistent with GMS802 H2O2 resistance and with a role for PerR as a transcriptional repressor. Cumulatively, these findings support a reciprocal relationship between PerR and SloR during the S. mutans oxidative stress response and begin to elucidate the fitness strategies that evolved to foster S. mutans persistence in the transient environments of the human oral cavity. IMPORTANCE In 2020, untreated dental caries, especially in the permanent dentition, ranked among the most prevalent infectious diseases worldwide, disproportionately impacting individuals of low socioeconomic status. Untreated caries can lead to systemic health problems and has been associated with extended school and work absences, inappropriate use of emergency departments, and an inability for military forces to deploy. Together with public health policy, research aimed at alleviating S. mutans-induced tooth decay is important because it can improve oral health (and overall health), especially in underserved populations. This research, focused on S. mutans metalloregulatory proteins and their gene targets, is significant because it can promote virulence gene control in an important oral pathogen, and contribute to the development of an anti-caries therapeutic that can reduce tooth decay.

TheStreptococcus mutansRhamnose-glucose Polysaccharide Plays an Important Role in Oxidative Stress Resistance and Iron Homeostasis

“…Further, the overlap of the motifs for PerR and Rex highlights the control these proteins have on rmlD expression. Canonically, PerR is considered a repressor, while Rex has been shown to act as an activator or repressor of gene expression, dependent on the gene being regulated (30, 32, 33, 35, 37, 38). Our results support these previous findings, where rmlD expression was elevated in the absence of PerR, or when its binding motif was disrupted, upon exposing a culture to H 2 O 2 .…”

“…PerR is a member of the Fur family of transcriptional regulators that regulate iron homeostasis and expression of oxidative stress response genes in streptococci (27)(28)(29)(30). The genes dpr (SMU.540), ahpCF (SMU.764-765), and sod (SMU.629) have all been shown to be negatively regulated, or repressed, by PerR (23,28,31,32). Loss of PerR in S. mutans has been shown to result in decreased susceptibility to hydrogen peroxide (23).…”

Molecular and regulatory mechanisms of oxidative stress adaptation in Streptococcus mutans

“…When S. mutans is threatened by H 2 O 2 produced by Streptococcus gordonii or S. sanguinis , SloR can activate the expression of S. mutans oxidative stress adaptation genes (such as dpr and sod ) at an early stage (Crepps et al., 2016). But caseinolytic protease (Clp) proteolytic systems degrade SloR proteins in the H 2 O 2 environment (Ruxin et al, 2021). Therefore, the regulation system of oxidative stress adaptation mechanism of S. mutans is compilated.…”

“…The upregulation of dpr was observed in perR single‐knockout or sloR and perR double‐knockout strains, and further reduced the ROS damage to cells (Brenot et al., 2007; Faulkner & Helmann, 2011; H. J. Wu et al., 2006). Furthermore, studies have shown that when S. mutans is exposed to H 2 O 2 , the perR gene is upregulated, and bind to specific sequences in the sloR operon to inhibit sloR transcription (Ruxin et al, 2021).…”

“…Furthermore, S. mutans has a variety of mechanisms, mainly including transcription factors SloR, PerR, Rex, and Spx (Bitoun & Wen, 2016;Crepps et al, 2016;Ganguly et al, 2020;Kajfasz et al, 2017Kajfasz et al, , 2021Ruxin et al, 2021), two-component systems (TCSs) (De Furio, 2017), and Cid and Lrg (Rice et al, 2017) to regulate the protective molecules expression, which helps S. mutans adapt to the oxidative stress. This study aimed to summarize the protective molecules and related regulatory mechanisms of oxidative stress adaptation of the cariogenic microorganism S. mutans.…”