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

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

Streptococcus gallolyticus subsp. gallolyticus is an emerging opportunistic pathogen responsible for septicemia and endocarditis in the elderly. Invasive infections by S. gallolyticus subsp. gallolyticus are strongly linked to the occurrence of colorectal cancer (CRC). It was previously shown that increased secondary bile salts under CRC conditions enhance the bactericidal activity of gallocin, a bacteriocin produced by S. gallolyticus subsp. gallolyticus, enabling it to colonize the mouse colon by outcompeting resident enterococci (L. Aymeric, F. Donnadieu, C. Mulet, L. du Merle, et al., Proc Natl Acad Sci U S A 115:E283-E291, 2018, https://doi.org/10.1073/pnas.1715112115). In a separate study, we showed that S. gallolyticus subsp. gallolyticus produces and secretes a 21-mer peptide that activates bacteriocin production (A. Proutière, L. du Merle, B. Périchon, H. Varet, et al., mBio 11:e03187-20, 2020, https://doi.org/10.1128/mBio.03187-20). This peptide was named CSP because of its sequence similarity with competence-stimulating peptides found in other streptococci. Here, we demonstrate that CSP is a bona fide quorum sensing peptide involved in activation of gallocin gene transcription. We therefore refer to CSP as GSP (gallocin-stimulating peptide). GSP displays some unique features, since its N-terminal amino acid lies three residues after the double glycine leader sequence. Here, we set out to investigate the processing and export pathway that leads to mature GSP. Heterologous expression in Lactococcus lactis of the genes encoding GSP and the BlpAB transporter is sufficient to produce the 21-mer form of GSP in the supernatant, indicating that S. gallolyticus subsp. gallolyticus BlpAB displays an atypical cleavage site. We also conducted the first comprehensive structure-activity relationship (SAR) analysis of S. gallolyticus subsp. gallolyticus GSP to identify its key structural features and found that unlike many other similar streptococci signaling peptides (such as CSPs), nearly half of the mature GSP sequence can be removed (residues 1 to 9) without significantly impacting the peptide activity.IMPORTANCE Streptococcus gallolyticus subsp. gallolyticus is an opportunistic pathogen associated with colorectal cancer (CRC) and endocarditis. S. gallolyticus subsp. gallolyticus utilizes quorum sensing (QS) to regulate the production of a bacteriocin (gallocin) and gain a selective advantage in colonizing the colon. In this article, we report (i) the first structure-activity relationship study of the S. gallolyticus subsp. gallolyticus QS pheromone that regulates gallocin production, (ii) evidence that the active QS pheromone is processed to its mature form by a unique ABC transporter and not processed by an extracellular protease, and (iii) supporting evidence of interspecies interactions between streptococcal pheromones. Our results revealed the minimal pheromone scaffold needed for gallocin activation and uncovered unique interactions between two streptococcal QS signals that warrant further study.

Toward understanding the signals of bacteriocin production by Streptococcus spp. and their importance in current applications

Microorganisms have developed quorum sensing (QS) systems to detect small signaling molecules that help to control access to additional nutrients and space in highly competitive polymicrobial niches. Many bacterial processes are QS-regulated; two examples are the highly related traits of the natural genetic competence state and the production of antimicrobial peptides such as bacteriocins. The Streptococcus genus is widely studied for its competence and for its ability to produce bacteriocins, as these antimicrobial peptides have significant potential in the treatment of infections caused by multiple-resistant pathogens, a severe public health issue. The transduction of a two-component system controls competence in streptococci: (1) ComD/E, which controls the competence in the Mitis and Anginosus groups, and (2) ComR/S, which performs the same function in the Bovis, Mutans, Salivarius, and Pyogenic groups. The cell-to-cell communication required for bacteriocin production in the Streptococcus groups is controlled mainly by a paralog of the ComD/E system. The relationships between pheromone signals and induction pathways are related to the bacteriocin production systems. In this review, we discuss the recent advances in the understanding of signaling and the induction of bacteriocin biosynthesis by QS regulation in streptococci. This information could aid in the design of better methods for the development and production of these antimicrobial peptides. It could also contribute to the analysis and emerging applications of bacteriocins in terms of their safety, quality, and human health benefits.

Emerging biosensors in detection of natural products

Natural products (NPs) are a valuable source in the food, pharmaceutical, agricultural, environmental, and many other industrial sectors. Their beneficial properties along with their potential toxicities make the detection, determination or quantification of NPs essential for their application. The advanced instrumental methods require time-consuming sample preparation and analysis. In contrast, biosensors allow rapid detection of NPs, especially in complex media, and are the preferred choice of detection when speed and high throughput are intended. Here, we review diverse biosensors reported for the detection of NPs. The emerging approaches for improving the efficiency of biosensors, such as microfluidics, nanotechnology, and magnetic beads, are also discussed. The simultaneous use of two detection techniques is suggested as a robust strategy for precise detection of a specific NP with structural complexity in complicated matrices. The parallel detection of a variety of NPs structures or biological activities in a mixture of extract in a single detection phase is among the anticipated future advancements in this field which can be achieved using multisystem biosensors applying multiple flow cells, sensing elements, and detection mechanisms on miniaturized folded chips.

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

Medicinal mushrooms have documented effects against different diseases, including infections and inflammatory disorders. The related Basidiomycota Agaricus blazei Murill (AbM), Hericium erinaceus (HE), and Grifola frondosa (GF) have been shown to exert antimicrobial activity against viral agents, Gram‐positive and Gram‐negative bacteria, and parasites in vitro and in vivo. Since the mechanism is immunomodulatory and not antibiotical, the mushrooms should be active against multi‐drug resistant microbes as well. Moreover, since these Basidiomycota also have anti‐inflammatory properties, they may be suited for treatment of the severe lung inflammation that often follows COVID‐19 infection. An AbM‐based mushroom extract (Andosan™), also containing HE and GF, has been shown to significantly reduce bacteraemia and increase survival in mice with pneumococcal sepsis, and to improve symptoms and quality of life in IBD patients via an anti‐inflammatory effect. Hence, such mushroom extracts could have prophylactic or therapeutic effect against the pneumonic superinfection and severe lung inflammation that often complicates COVID‐19 infection. Here, we review antimicrobial and anti‐inflammatory properties of AbM, HE and GF mushrooms, which could be used for the battle against COVID‐19.

Biological and chemical diversity go hand in hand: Basidiomycota as source of new pharmaceuticals and agrochemicals

The Basidiomycota constitutes the second largest higher taxonomic group of the Fungi after the Ascomycota and comprises over 30.000 species. Mycelial cultures of Basidiomycota have already been studied since the 1950s for production of antibiotics and other beneficial secondary metabolites. Despite the fact that unique and selective compounds like pleuromutilin were obtained early on, it took several decades more until they were subjected to a systematic screening for antimicrobial and anticancer activities. These efforts led to the discovery of the strobilurins and several hundreds of further compounds that mainly constitute terpenoids. In parallel the traditional medicinal mushrooms of Asia were also studied intensively for metabolite production, aimed at finding new therapeutic agents for treatment of various diseases including metabolic disorders and the central nervous system. While the evaluation of this organism group has in general been more tedious as compared to the Ascomycota, the chances to discover new metabolites and to develop them further to candidates for drugs, agrochemicals and other products for the Life Science industry have substantially increased over the past decade. This is owing to the revolutionary developments in -OMICS techniques, bioinformatics, analytical chemistry and biotechnological process technology, which are steadily being developed further. On the other hand, the new developments in polythetic fungal taxonomy now also allow a more concise selection of previously untapped organisms. The current review is dedicated to summarize the state of the art and to give an outlook to further developments.