The leaderless communication peptide (LCP) class of quorum-sensing peptides is broadly distributed among Firmicutes

The MutRS quorum-sensing system controls lantibiotic mutacin production in the human pathogen Streptococcus mutans

Microbes use quorum-sensing systems to respond to ecological and environmental changes. In the oral microbiome, the pathogenic bacterium Streptococcus mutans uses quorum-sensing to control the production of bacteriocins. These antimicrobial peptides kill off ecological competitors and allow S. mutans to dominate the microenvironment of dental plaques and form dental caries. One class of bacteriocins produced by S. mutans, the lantibiotic mutacins, are particularly effective at killing due to their broad spectrum of activity. Despite years of study, the regulatory mechanisms governing production of lantibiotic mutacins I, II, and III in S. mutans have never been elucidated. We identified a distinct class of quorum-sensing system, MutRS, that regulates mutacins and is widespread among the streptococci. We demonstrate that MutRS systems are activated by a short peptide pheromone (Mutacin Stimulating Peptide) and show that MutRS controls production of three separate lantibiotic mutacins in three different strains of S. mutans. Finally, we show that paralogous MutRS systems participate in inter- and intrastrain crosstalk, providing further evidence of the interplay between quorum-sensing systems in the oral streptococci.

Entire Encapsulation of Thymopentin by Extended Biphen[3]arene Carboxylate for Improving Plasma Stability

Peptide-based therapy is appealing in modern medicine owing to its high activity and excellent biocompatibility. Poor stability, leading to unacceptable bioavailability, severely constrains its clinical application. Here, we proposed a general supramolecular approach for improving the plasma resistance of a commercially available peptide agent, thymopentin. The 1H NMR results indicated that the large-sized extended biphen[3]arene carboxylate (ExBP3C) can entirely encapsulate this peptide at its main chain with a binding stoichiometry of 1:1 and Ka value of (1.87 ± 0.15) × 105 M-1, which varied radically from recognizing specific amino acid residues by carboxylatopillar[5]arene (CP5A). Notably, host-guest complexation by ExBP3C could maintain 24.85% of the original thymopentin amount for 60 min in the presence of rat plasma, whereas free thymopentin, or co-dosed with CP5A and cucurbit[7]uril, underwent rapid degradation and became undetectable within just 30 min. In addition, cytotoxicity and hemolysis assays preliminary demonstrated that the employment of ExBP3C as a supplementary material was relatively nontoxic at a cellular level.

Advanced oxidation process/coagulation coupled with membrane distillation (AOP/Coag-MD) for efficient ammonia recovery: Elucidating biofouling control performance and mechanism

The inadequate understanding of the biofouling formation mechanism and the absence of effective control have inhibited the commercial application of membrane distillation (MD). In this study, an advanced oxidation process (AOP)/coagulation-coupled (Coag) membrane distillation system was proposed and exhibited the potential for MD ammonia recovery (recovery rate: 94.1%). Extracellular polymeric substances (EPS) and soluble microbial products (SMP) components such as humic acid and tryptophan-like proteins were disrupted and degraded in the digestate. The curtailment and sterilizing efficiency of AOP on biofilm growth was also verified by optical coherence tomography (OCT) in situ real-time monitoring and confocal laser scanning microscopy (CLSM). Peroxymonosulfate (PMS) was activated to generate sulfate (SO4•-) and hydroxyl radicals (HO•), which altered the microbial community. After oxidative treatment, 16 S rRNA sequencing indicated that the dominant phylum of the microbial community evolved into Firmicutes. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis demonstrated that free radicals produced by PMS could disrupt cells' signaling molecules and interactions. In conjunction with these analyses, the mechanisms of response to free radical attack by Gram-negative bacteria, Gram-positive bacteria, and fungi were revealed. This research provided new insights into the field of membrane fouling control for membrane technology resource recovery processes, broadening the impact of AOP applications on microbiological response and fate in the environment.

Engineered probiotic overcomes pathogen defences using signal interference and antibiotic production to treat infection in mice

Probiotic supplements are suggested to promote human health by preventing pathogen colonization. However, the mechanistic bases for their efficacy in vivo are largely uncharacterized. Here using metabolomics and bacterial genetics, we show that the human oral probiotic Streptococcus salivarius K12 (SAL) produces salivabactin, an antibiotic that effectively inhibits pathogenic Streptococcus pyogenes (GAS) in vitro and in mice. However, prophylactic dosing with SAL enhanced GAS colonization in mice and ex vivo in human saliva. We showed that, on co-colonization, GAS responds to a SAL intercellular peptide signal that controls SAL salivabactin production. GAS produces a secreted protease, SpeB, that targets SAL-derived salivaricins and enhances GAS survival. Using this knowledge, we re-engineered probiotic SAL to prevent signal eavesdropping by GAS and potentiate SAL antimicrobials. This engineered probiotic demonstrated superior efficacy in preventing GAS colonization in vivo. Our findings show that knowledge of interspecies interactions can identify antibiotic- and probiotic-based strategies to combat infection.