Reduced Glutathione Mediates Resistance to H ₂ S Toxicity in Oral Streptococci

Abstract

Periodontal disease is associated with changes in the composition of the oral microflora, where health-associated oral streptococci decrease while Gram-negative anaerobes predominate in disease. A key feature of periodontal disease-associated anaerobes is their ability to produce hydrogen sulfide (H 2 S) abundantly as a by-product of anaerobic metabolism. So far, H 2 S has been reported to be either cytoprotective or cytotoxic by modulating bacterial antioxidant defense systems. Although oral anaerobes produce large amounts of H 2 S, the potential effects of H 2 S on oral streptococci are currently unknown. The aim of this study was to determine the effects of H 2 S on the survival and biofilm formation of oral streptococci. The growth and biofilm formation of Streptococcus mitis and Streptococcus oralis were inhibited by H 2 S. However, H 2 S did not significantly affect the growth of Streptococcus gordonii or Streptococcus sanguinis. The differential susceptibility of oral streptococci to H 2 S was attributed to differences in the intracellular concentrations of reduced glutathione (GSH). In the absence of GSH, H 2 S elicited its toxicity through an iron-dependent mechanism. Collectively, our results showed that H 2 S exerts antimicrobial effects on certain oral streptococci, potentially contributing to the decrease in health-associated plaque microflora.

Hydrogen Sulfide Sensitizes Acinetobacter baumannii to Killing by Antibiotics

“…Generally, low concentrations (micromolar) of H 2 S are regarded as cytoprotective while high concentrations (millimolar) are cytotoxic (Ritter, 2010). Several studies have also established that H 2 S can either be cytoprotective or cytotoxic to microbes (Shatalin et al, 2011;Wu et al, 2015;Ooi and Tan, 2016;Fu et al, 2018). Shatalin et al (2011) showed that H 2 S is produced endogenously by orthologs of CBS, CSE, or MST in B. anthracis, P. aeruginosa, S. aureus, and E. coli.…”

H2S and reactive sulfur signaling at the host-bacterial pathogen interface

“…Further studies are required to establish the generality of this adaptive response across a wider range of organisms. Others have posited that H 2 S-mediated cytoprotection occurs via sequestration of the prooxidant free Fe(II) (23,98); however, this remains incompletely understood.…”

Molecular Adaptations of Bacterial Mercuric Reductase to the Hypersaline Kebrit Deep in the Red Sea

“…Hydrogen sulfide has been shown to mediate several physiological effects in eukaryotic cells (30,31), including the promotion of glutathione production (32). In prokaryotic cells, it has been shown that reduced glutathione mediates resistance to H 2 S toxicity in oral streptococci (33). Hence, intracellular thiols are likely to be abundant in Kebrit's microorganisms.…”