Modification of the Streptococcus mutans transcriptome by LrgAB and environmental stressors

Abstract

The Streptococcus mutans Cid/Lrg system is central to the physiology of this cariogenic organism, affecting oxidative stress resistance, biofilm formation and competence. Previous transcriptome analyses of lytS (responsible for the regulation of lrgAB expression) and cidB mutants have revealed pleiotropic effects on carbohydrate metabolism and stress resistance genes. In this study, it was found that an lrgAB mutant, previously shown to have diminished aerobic and oxidative stress growth, was also much more growth impaired in the presence of heat and vancomycin stresses, relative to wild-type, lrgA and lrgB mutants. To obtain a more holistic picture of LrgAB and its involvement in stress resistance, RNA sequencing and bioinformatics analyses were used to assess the transcriptional response of wild-type and isogenic lrgAB mutants under anaerobic (control) and stress-inducing culture conditions (aerobic, heat and vancomycin). Hierarchical clustering and principal components analyses of all differentially expressed genes revealed that the most distinct gene expression profiles between S. mutans UA159 and lrgAB mutant occurred during aerobic and high-temperature growth. Similar to previous studies of a cidB mutant, lrgAB stress transcriptomes were characterized by a variety of gene expression changes related to genomic islands, CRISPR-C as systems, ABC transporters, competence, bacteriocins, glucosyltransferases, protein translation, tricarboxylic acid cycle, carbohydrate metabolism/storage and transport. Notably, expression of lrgAB was upregulated in the wild-type strain under all three stress conditions. Collectively, these results demonstrate that mutation of lrgAB alters the transcriptional response to stress, and further support the idea that the Cid/Lrg system acts to promote cell homeostasis in the face of environmental stress.

Extracellular matrix influence in Streptococcus mutans gene expression in a cariogenic biofilm

“…In addition, it has been shown that a ΔlrgAB mutant presented transcriptomic profile distinct from the ΔlytS mutant, even though LytST controls expression of lrgAB, 29 suggesting that changes in gene expression by the mutation of lrgAB could be independent of LytST. 55 As pointed out earlier, it is possible that changes on the cell membrane could explain some of the distinct and even unexpected expression patterns, and hence, future research on membrane composition and structure deserves attention.…”

Acetate and Potassium Modulate the Stationary-Phase Activation of lrgAB in Streptococcus mutans

“…To measure growth-dependent expression of genes related to pyruvate metabolism, cells were harvested in early-exponential and -stationary growth phases. Extraction of RNA, qPCR, and data analysis were performed as described elsewhere Ahn and Rice, 2016;Rice et al, 2017). Expression was normalized against an internal standard (gyrA).…”

Inactivation ofStreptococcus mutansgeneslytSTanddltADimpairs its pathogenicityin vivo

“…Furthermore, as the ΔgtfB biofilm aged, the expression of lytS decreased, being inversely proportional to the increase of expression recorded for lrgAB, which was not observed for UA159 biofilms. Even though LytST controls the expression of lrgAB, a ΔlrgAB mutant presented a distinct transcriptomic profile from the ΔlytS mutant [45], suggesting that changes in gene expression by the mutation of lrgAB could be independent of LytST [59]. Further comparison of transcriptomics and proteomics of a ΔlrgAB mutant (vs. the parental strain) subjected to distinct oxidative, heat and antimicrobial stresses indicated 'that adaptation to a new environment may require radical proteome turnover or metabolic remodeling' [50].…”