Screening for inhibitors of mutacin synthesis in Streptococcus mutans using fluorescent reporter strains

Abstract

BackgroundWithin the polymicrobial dental plaque biofilm, bacteria kill competitors by excreting mixtures of bacteriocins, resulting in improved fitness and survival. Inhibiting their bacteriocin synthesis might therefore be a useful strategy to eliminate specific pathogens. We used Streptococcus mutans, a highly acidogenic inhabitant of dental plaque, as a model and searched for natural products that reduced mutacin synthesis. To this end we fused the promoter of mutacin VI to the GFP+ gene and integrated the construct into the genome of S. mutans UA159 by single homologous recombination.ResultsThe resulting reporter strain 423p - gfp + was used to screen 297 secondary metabolites from different sources, mainly myxobacteria and fungi, for their ability to reduce the fluorescence of the fully induced reporter strain by > 50% while growth was almost unaffected (> 90% of control). Seven compounds with different chemical structures and different modes of action were identified. Erinacine C was subsequently validated and shown to inhibit transcription of all three mutacins of S. mutans. The areas of the inhibition zones of the sensor strains S. sanguinis and Lactococcus lactis were reduced by 35% to 61% in comparison to controls in the presence of erinacine C, demonstrating that the amount of active mutacins in the culture supernatants of S. mutans was reduced. Erinacines are cyathane diterpenes that were extracted from cultures of the edible mushroom Hericium erinaceus. They have anti-inflammatory, antimicrobial and neuroprotective effects. For erinacine C, a new biological activity was found here.ConclusionsWe demonstrate the successful development of a whole-cell fluorescent reporter for the screening of natural compounds and report that erinacine C suppresses mutacin synthesis in S. mutans without affecting cell viability.Electronic supplementary materialThe online version of this article (10.1186/s12866-018-1170-3) contains supplementary material, which is available to authorized users.

Secretion, maturation and activity of a quorum-sensing peptide (GSP) inducing bacteriocins transcription inStreptococcus gallolyticus

“…Indeed, GSP 21-mer peptide EC50 (2.96 nm) was 18 around 100 times lower than GSP 24-mer EC50 (287 nM), indicating that the 21-mer is 19 significantly more active than the 24-mer ( Table 1). These results imply that GSP maturation to a 20 21-mer peptide increases GSP efficiency as compared to the 24-mer peptide, but is not absolutely 21 required, unlike the CSP/MIP of S. mutans (28,29 An ABC transporter is responsible for the secretion of GSP and gallocin peptides 27 We next aimed at determining how GSP was secreted and processed into a 21-mer peptide in Sgg 28 UCN34. In S. mutans, the equivalent 21-mer MIP peptide encoded by comC is secreted by a 29 specific ABC transporter composed of ComA and ComB proteins ( Fig.…”

Can medicinal mushrooms have prophylactic or therapeutic effect against COVID‐19 and its pneumonic superinfection and complicating inflammation?

“…40 When testing natural products against synthesis of the bacteriocin mutacin by Streptococcus mutans in dental plaque biofilm, it was found to be inhibited by erinacine C from HE. 43 Quorum sensing plays an important role for virulence, biofilm formation and survival of many pathogenic bacteria, including Gram-negative Pseudomonas aeruginosa. 44 Interestingly, an AbM extract has been shown to have antiquorum sensing effect as demonstrated by reduction of virulence factors of P aeruginosa and its biofilm forming capability, which may be used as weapon against such pathogens.…”

“…When testing natural products against synthesis of the bacteriocin mutacin by Streptococcus mutans in dental plaque biofilm, it was found to be inhibited by erinacine C from HE 43 . Quorum sensing plays an important role for virulence, biofilm formation and survival of many pathogenic bacteria, including Gram‐negative Pseudomonas aeruginosa 44 .…”

Secretion, Maturation, and Activity of a Quorum Sensing Peptide (GSP) Inducing Bacteriocin Transcription in Streptococcus gallolyticus

“…For example, the comABCDE circuitry in Streptococcus mutans regulates the production of bacteriocins called mutacins directly and competence through activation of the comRS circuitry ( 14 , 22 – 25 ). This observation has led to the proposal that the S. mutans CSP be renamed mutacin-inducing peptide (MIP) ( 14 , 26 , 27 ). Additionally, it was shown that the secreted 21-mer CSP/MIP peptide is inactive and requires further processing by the streptococcal extracellular protease (SepM), which cleaves the three C-terminal residues of 21-mer CSP/MIP to generate the active 18-mer CSP/MIP ( 28 , 29 ).…”