Effect of Different Glucose Concentrations on Small RNA Levels and Adherence of Streptococcus mutans

Small regulatory RNAs are mediators of the Streptococcus mutans SloR regulon

Dental caries is among the most prevalent chronic infectious diseases worldwide. Streptococcus mutans , the chief causative agent of caries, uses a 25 kDa manganese dependent SloR protein to coordinate the uptake of essential manganese with the transcription of its virulence attributes. Small non-coding RNAs (sRNAs) can either enhance or repress gene expression and reports in the literature ascribe an emerging role for sRNAs in the environmental stress response. Herein, we identify 18-50 nt sRNAs as mediators of the S. mutans SloR and manganese regulons. Specifically, the results of sRNA-seq revealed 56 sRNAs in S. mutans that were differentially transcribed in the SloR-proficient UA159 and SloR-deficient GMS584 strains, and 109 sRNAs that were differentially expressed in UA159 cells grown in the presence of low versus high manganese. We describe SmsR1532 and SmsR1785 as SloR- and/or manganese-responsive sRNAs that are processed from large transcripts, and that bind SloR directly in their promoter regions. The predicted targets of these sRNAs include regulators of metal ion transport, growth management via a toxin-antitoxin operon, and oxidative stress tolerance. These findings support a role for sRNAs in coordinating intracellular metal ion homeostasis with virulence gene control in an important oral cariogen.

IMPORTANCE

Small regulatory RNAs (sRNAs) are critical mediators of environmental signaling, particularly in bacterial cells under stress, but their role in Streptococcus mutans is poorly understood. S. mutans, the principal causative agent of dental caries, uses a 25 kDa manganese-dependent protein, called SloR, to coordinate the regulated uptake of essential metal ions with the transcription of its virulence genes. In the present study, we identified and characterize sRNAs that are both SloR- and manganese-responsive. Taken together, this research can elucidate the details of regulatory networks that engage sRNAs in an important oral pathogen, and that can enable the development of an effective anti-caries therapeutic.

[Regulatory role of small RNA srn821978 in mutacin IV expression in Streptococcus mutans]

OBJECTIVE

To analyze the role of small RNA srn821798 in posttranscriptional regulation of mutacin IV expression in Streptococcus mutans.

METHODS

The potential target genes of srn821978 were predicted using RNAhybrid, RNAPredator and IntaRNA. We collected 10 Streptococcus mutans (S.muans) strains with high expression of mutacin IV and another 10 S.muans strains that did not express mutacin IV screened by inhibition zone test, and the expression levels of srn821798 and the candidate target genes in these strains were detected by qPCR. Using synthesized mimics and inhibitors of srn821798, we constructed S.muans strains with high or low srn821798 expression via electroporation based on the standard strain of S.muans UA159, and analyzed the expression levels of srn821798 and its candidate target genes in these strains. We also examined the binding ability of srn821798 to its target gene sepM using electrophoresis and a dual- luciferase reporter system.

RESULTS

The expression levels of the candidate target genes of srn821798 including sepM, comD, comE, nlmA and nlmB were significantly higher while the expression level of srn821798 was significantly lower in clinical S.muans strains with high expression of mutacin IV than in those without mutacin IV expression (P < 0.05). Although the expression levels of the candidate target genes in strains with up- regulated or down- regulated srn821798 expression did not differ significantly from those in the standard strain, the expression level of sepM showed a trend of differential distribution, and srn821798 was predicted to have a strong binding ability to sepM action site.

CONCLUSION

srn821798 may play a regulatory role in the expression of mutacin IV in S.muans, but the underlying mechanism remains to be explored.

Small regulatory RNAs of oral streptococci and periodontal bacteria

Small regulatory RNAs (sRNAs) belong to a family of non-coding RNAs, and many of which regulate expression of genes via interaction with mRNA. The recent popularity of high-throughput next generation sequencers have presented abundant sRNA-related data, including sRNAs of several different oral bacterial species. Some sRNA candidates have been validated in terms of their expression and interaction with target mRNAs. Since the oral cavity is an environment constantly exposed to various stimuli, such as fluctuations in temperature and pH, and osmotic pressure, as well as changes in nutrient availability, oral bacteria require rapid control of gene expression for adaptation to such diverse conditions, while regulation via interactions of sRNAs with mRNA provides advantages for rapid adaptation. This review summarizes methods effective for identification and validation of sRNAs, as well as sRNAs identified to be associated with oral bacterial species, including cariogenic and periodontal pathogens, together with their confirmed and putative target genes.

Effect of different salivary glucose concentrations on dual-species biofilms of Candida albicans and Streptococcus mutans

Diabetes mellitus is one of the most prevalent diseases worldwide. The glucose levels found in the blood of diabetic patients can be reflected in the saliva, which can favor biofilm growth and predispose denture wearers to oral candidiasis. This study aimed to evaluate the effect of different salivary glucose concentrations on dual-species biofilms of Candida albicans and Streptococcus mutans. A 96-h biofilm was developed on acrylic resin specimens exposed to 'feast' (10% sucrose) and 'famine' periods. Biofilms were constantly exposed to salivary glucose concentrations equivalent to 0, 20, 60 and 100 mM. Higher salivary glucose concentrations resulted in increased counts of C. albicans and a higher quantity of insoluble extracellular polysaccharides. All biofilms presented high phospholipase activity. The biofilms were characterized by the predominance of yeast cells and microcolonies in all the groups analyzed with co-localization of both species. Higher salivary glucose concentrations formed more robust and potentially virulent biofilms.

Recent Research Advances in Small Regulatory RNAs in Streptococcus

Small non-coding RNAs (sRNAs) are a class of regulatory RNAs 20-500 nucleotides in length, which have recently been discovered in prokaryotic organisms. sRNAs are key regulators in many biological processes, such as sensing various environmental changes and regulating intracellular gene expression through binding target mRNAs or proteins. Bacterial sRNAs have recently been rapidly mined, thus providing new insights into the regulatory network of biological functions in prokaryotes. Although most bacterial sRNAs have been discovered and studied in Escherichia coli and other Gram-negative bacteria, sRNAs have increasingly been predicted and verified in Gram-positive bacteria in the past decade. The genus Streptococcus includes many commensal and pathogenic Gram-positive bacteria. However, current understanding of sRNA-mediated regulation in Streptococcus is limited. Most known sRNAs in Streptococcus are associated with the regulation of virulence. In this review, we summarize recent advances in understanding of the functions and mechanisms of sRNAs in Streptococcus, and we discuss the RNA chaperone protein and synthetic sRNA-mediated gene regulation, with the aim of providing a reference for the study of microbial sRNAs.