Understanding LrgAB Regulation of Streptococcus mutans Metabolism

Co-transcribed genes SA1833-SA1832 promote persister formation by regulating the transcription of holin-like gene lrgA in methicillin-resistant Staphylococcus aureus strain N315

Staphylococcus aureus, a facultative anaerobic gram-positive bacterial pathogen, has posed major threat to public health worldwide. Upon S. aureus infection, the host immune system is activated for clearance. However, intracellular S. aureus, which remains viable for an extended time, has evolved the ability to escape from immune response and extracellular antibiotics. One of possible strategies is the formation of persisters. Persistence is one of the major causes of S. aureus relapse infection but the underlying mechanisms remain obscure. Here, we identified two co-transcribed genes SA1833-SA1832 that are involved in persister formation in S. aureus. Dysfunction of SA1833 and/or SA1832 significantly reduces persister formation in the presence of ceftizoxime. Additionally, we found that the expression of SA1833 and SA1832 under the induction of oxidative stress and SOS response is strictly regulated by the LexA-RecA pathway. Interestingly, SA1833-SA1832 contributes to persister formation in an lrgA-dependent manner. Moreover, the mouse RAW264.7 macrophage infection model indicated that disrupting SA1833-SA1832 inhibits S. aureus from infecting macrophages and impairs its ability to survive in the intracellular environment.

Cariogenic potential of the Streptococcus mutans Cid/Lrg system: an in vivo animal case study

In our prior study using a dual-species (Streptococcus mutans/Streptococcus gordonii) competitive mouse caries model to investigate the contribution of S. mutans LrgAB to in vivo fitness, S. mutans wild-type and ΔlrgAB mutants consistently outnumbered S. gordonii and had high caries scores, even though the ΔlrgAB mutant is highly sensitive to oxidative stress. To determine whether the highly cariogenic sucrose diet used in the previous study masked the contribution of LrgAB to competitive fitness of S. mutans against S. gordonii, we recapitulated our previous mouse caries experiment with a modification in which 4% sucrose drinking water was replaced with sterile water, hypothesized to decrease the frequency of exposure of mice to sucrose, a determinant in the cariogenicity of S. mutans. Given that both S. mutans ΔlrgAB and ΔcidB mutants are sensitive to oxidative stress and share similar transcriptional profiles, these strains, as well as wild-type UA159, were tested in this modified dual-species mouse caries model. When comparing between groups the colonization within molar dental biofilms of S. mutans strains, ΔlrgAB mutant was at a level similar to the wild type, whereas S. mutans ΔcidB was modestly lower than both wild-type and S. mutans ΔlrgAB. The severity of total sulcal caries in both the ∆cidB and ∆lrgAB mutant infections was significantly lower than that of wild type. These results demonstrate that the Cid/Lrg system aids in S. mutans fitness against S. gordonii and caries potential in vivo, a phenotype likely masked in our previous study by more frequent exposure to sucrose.IMPORTANCEThe development of a mature biofilm on the tooth surface is the central event in the pathogenesis of dental caries, which primarily requires that cariogenic organisms withstand the limited resources or environmental fluctuations experienced in the oral cavity. The sensitive and heterogeneous response of the cid and lrg operons to complex external signals has been hypothesized to trigger differentiation of the Streptococcus mutans biofilm community into distinct functional subpopulations to promote survival and persistence of the S. mutans community when challenged by an unfavorable environment. The study described herein enlightens our understanding of how Cid/Lrg contributes to S. mutans pathogenic potential in vivo (caries development), warranting further research regarding the adaptive role of Cid/Lrg system in human oral biofilms toward the development of anti-caries strategies directed at the Cid/Lrg system.

Aspects of oral streptococcal metabolic diversity: Imagining the landscape beneath the fog

It is widely acknowledged that the human-associated microbial community influences host physiology, systemic health, disease progression, and even behavior. There is currently an increased interest in the oral microbiome, which occupies the entryway to much of what the human initially encounters from the environment. In addition to the dental pathology that results from a dysbiotic microbiome, microbial activity within the oral cavity exerts significant systemic effects. The composition and activity of the oral microbiome is influenced by (1) host-microbial interactions, (2) the emergence of niche-specific microbial "ecotypes," and (3) numerous microbe-microbe interactions, shaping the underlying microbial metabolic landscape. The oral streptococci are central players in the microbial activity ongoing in the oral cavity, due to their abundance and prevalence in the oral environment and the many interspecies interactions in which they participate. Streptococci are major determinants of a healthy homeostatic oral environment. The metabolic activities of oral Streptococci, particularly the metabolism involved in energy generation and regeneration of oxidative resources vary among the species and are important factors in niche-specific adaptations and intra-microbiome interactions. Here we summarize key differences among streptococcal central metabolic networks and species-specific differences in how the key glycolytic intermediates are utilized.

A functional promoter from the archaeon Halobacterium salinarum is also transcriptionally active in E. coli

Background

Archaea form a third domain of life that is distinct from Bacteria and Eukarya. So far, many scholars have elucidated considerable details about the typical promoter architectures of the three domains of life. However, a functional promoter from the archaeon Halobacterium salinarum has never been studied in Escherichia coli.

Results

This paper found that the promoter of Halobacterium salinarum showed a promoter function in Escherichia coli. This Escherichia coli promoter structure contains − 10 box, -10 box extension and − 29 elements, however, no -35 box. The − 29 element is exercised by the TATA box in archaea. And we isolated the RM10 fragment that possessed the fusion characteristics of bacteria and archaea, which was overlapped with functionality of TATA box and − 29 elements.

Conclusions

The − 29 element reflects the evolutionary relationship between the archaeal promoter and the bacterial promoter. The result possibly indicated that there may be a certain internal connection between archaea and bacteria. We hypothesized that it provided a new viewpoint of the evolutionary relationship of archaea and other organisms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02489-y.

Testing of candidate probiotics to prevent dental caries induced by Streptococcus mutans in a mouse model

AIMS

We evaluated two species of human oral commensal streptococci in protection against dental caries induced by Streptococcus mutans.

METHODS AND RESULTS

Candidate probiotics, Streptococcus sp. A12, Streptococcus sanguinis BCC23 and an arginine deiminase mutant of BCC23 (∆arcADS) were tested for their ability to reduce S. mutans-induced caries in an established mouse model. Mice were colonized with a probiotic, challenged with S. mutans, then intermittently reinoculated with a probiotic strain. Oral colonization of each strain and autochthonous bacteria was assessed by qPCR. Both BCC23 strains, but not A12, were associated with markedly reduced sulcal caries, persistently colonized mucosal and dental biofilms, and significantly lowered S. mutans counts. All three strains enhanced mucosal colonization of autochthonous bacteria. In a follow-up experiment, when S. mutans was established first, dental and mucosal colonization of S. mutans was unaltered by a subsequent challenge with either BCC23 strain. Results between BCC23 and BCC23 ∆arcADS were equivalent.

CONCLUSIONS

BCC23 is a potential probiotic to treat patients at high caries risk. Its effectiveness is independent of ADS activity, but initial dental cleaning to enhance establishment in dental biofilms may be required.

SIGNIFICANCE AND IMPACT OF THE STUDY

In vivo testing of candidate probiotics is highly informative, as effectiveness is not always reflected by genotype or in vitro behaviors.

Selective Fermentation of Lactobacillus and Streptococcus In Vitro: Effects of Chinese Fermented Glutinous Rice on the Growth Promotion of Potential Probiotics

A functional Chinese fermented glutinous rice has been developed with the supplementation of Fu brick tea (CRW-FBT). In this study, we aimed to evaluate its effect on the growth of potential probiotic strains in the Lactobacillus, Streptococcus, and Weissella genus, compared with traditional Chinese fermented glutinous rice (CRW). The growth profiles of lactic acid bacteria were analyzed based on fermentations in vitro, and the optical densities were recorded at 600 nm during the whole fermentation. Growth curve, maximum OD600 nm, and growth rate were measured and compared among samples with different ratios of CRW-FBT and CRW addition. Through the multiple analysis of growth parameters, we found that all the tested strains obtained better growth results when CRW-FBT was supplemented to the media, compared with the CRW and basic media. The bacterial growth was promoted by exhibiting the shortened lag time, prolonged logarithmic phase and stationary phase, and increased growth rate and cell density, as well as the better performance after 24 h and 48 h fermentation. Besides, short-chain fatty acids and organic acids in CRW-FBT were founded. Our work demonstrated the positive effect of Fu brick tea supplemented in the CRW and illustrated its beneficial role in the food fermentation industry for the purpose of microorganism enrichment and the improvement of microbial metabolism.

Spontaneous Mutants of Streptococcus sanguinis with Defects in the Glucose-Phosphotransferase System Show Enhanced Post-Exponential-Phase Fitness

Genetic truncations in a gene encoding a putative glucose-phosphotransferase system (PTS) protein (manL, EIIAB^Man) were identified in subpopulations of two separate laboratory stocks of Streptococcus sanguinis SK36; the mutants had reduced PTS activities on glucose and other monosaccharides. To understand the emergence of these mutants, we engineered deletion mutants of manL and showed that the ManL-deficient strain had improved bacterial viability in the stationary phase and was better able to inhibit the growth of the dental caries pathogen Streptococcus mutans. Transcriptional analysis and biochemical assays suggested that the manL mutant underwent reprograming of central carbon metabolism that directed pyruvate away from production of lactate, increasing production of hydrogen peroxide (H₂O₂) and excretion of pyruvate. Addition of pyruvate to the medium enhanced the survival of SK36 in overnight cultures. Meanwhile, elevated pyruvate levels were detected in the cultures of a small but significant percentage (∼10%) of clinical isolates of oral commensal bacteria. Furthermore, the manL mutant showed higher expression of the arginine deiminase system than the wild type, which enhanced the ability of the mutant to raise environmental pH when arginine was present. To our surprise, significant discrepancies in genome sequence were identified between strain SK36 obtained from ATCC and the sequence deposited in GenBank. As the conditions that are likely associated with the emergence of spontaneous manL mutations, i.e., excess carbohydrates and low pH, are those associated with caries development, we propose that glucose-PTS strongly influences commensal-pathogen interactions by altering the production of ammonia, pyruvate, and H₂O₂. IMPORTANCE A health-associated dental microbiome provides a potent defense against pathogens and diseases. Streptococcus sanguinis is an abundant member of a health-associated oral flora that antagonizes pathogens by producing hydrogen peroxide. There is a need for a better understanding of the mechanisms that allow bacteria to survive carbohydrate-rich and acidic environments associated with the development of dental caries. We report the isolation and characterization of spontaneous mutants of S. sanguinis with impairment in glucose transport. The resultant reprograming of the central metabolism in these mutants reduced the production of lactic acid and increased pyruvate accumulation; the latter enables these bacteria to better cope with hydrogen peroxide and low pH. The implications of these discoveries in the development of dental caries are discussed.

Murine Salivary Amylase Protects Against Streptococcus mutans-Induced Caries

Saliva protects dental surfaces against cavities (i. e., dental caries), a highly prevalent infectious disease frequently associated with acidogenic Streptococcus mutans. Substantial in vitro evidence supports amylase, a major constituent of saliva, as either protective against caries or supporting caries. We therefore produced mice with targeted deletion of salivary amylase (Amy1) and determined the impact on caries in mice challenged with S. mutans and fed a diet rich in sucrose to promote caries. Total smooth surface and sulcal caries were 2.35-fold and 1.79-fold greater in knockout mice, respectively, plus caries severities were twofold or greater on sulcal and smooth surfaces. In in vitro experiments with samples of whole stimulated saliva, amylase expression did not affect the adherence of S. mutans to saliva-coated hydroxyapatite and slightly increased its aggregation in solution (i.e., oral clearance). Conversely, S. mutans in biofilms formed in saliva with 1% glucose displayed no differences when cultured on polystyrene, but on hydroxyapatite was 40% less with amylase expression, suggesting that recognition by S. mutans of amylase bound to hydroxyapatite suppresses growth. However, this effect was overshadowed in vivo, as the recoveries of S. mutans from dental plaque were similar between both groups of mice, suggesting that amylase expression helps decrease plaque acids from S. mutans that dissolve dental enamel. With amylase deletion, commensal streptococcal species increased from ~75 to 90% of the total oral microbiota, suggesting that amylase may promote higher plaque pH by supporting colonization by base-producing oral commensals. Importantly, collective results indicate that amylase may serve as a biomarker of caries risk.