Biology subjects

du Merle, L.

Publications and source records attributed to du Merle, L..

6 recordsLinked to original sources

bioRxiv2026

A Seven-Protein Assembly Promotes Stability, Neutralisation and Secretion of the T7SSb LXG-effector TelE

Streptococcus gallolyticus subsp. gallolyticus (SGG) is a gut pathobiont associated with colorectal cancer. Like many Firmicutes, SGG utilizes a specialized Type VII Secretion System (T7SSb) to export WXG100 and LXG proteins, the latter involved in bacterial competition. We previously identified TelE, an LXG protein whose C-terminus mediates membrane pore formation in Escherichia coli. In SGG UCN34, TelE (Gallo_0562) is co-expressed with six proteins (Gallo_0559 to Gallo_0565), including its immunity protein TipE (Gallo_0565). Here we show that the absence of those co-expressed proteins affects TelE stability and secretion. These proteins associate with TelE to form a soluble and stable seven-protein complex. Gallo_0559 and Gallo_0560 interact with the N-terminal LXG domain of TelE, Gallo_0561 binds to its central region, while the six-transmembrane protein Gallo_0563, together with Gallo_0564 and TipE associates with its C-terminal domain. These findings describe a new modular complex that stabilizes TelE while reducing its toxicity and optimizing its T7SSb-mediated delivery.

microbiology↗

bioRxiv2025

Colorectal Cancer-Associated Streptococcus gallolyticus: A Hidden Diversity Exposed

Streptococcus gallolyticus subsp. gallolyticus (SGG) is a bacterial pathogen implicated in bacteremia and endocarditis, and is often associated with colon tumors in elderly individuals. The development of colorectal cancer (CRC) has been linked to intestinal dysbiosis, characterized by increased proportions of SGG and other intestinal microbes. In this study, we present the complete nucleotide sequence of five novel clinical isolates of SGG associated with colorectal cancer, revealing unexpected genetic diversity. Sequencing an additional 30 SGG clinical isolates provided a more comprehensive description of this genetic diversity. We did not identify a pathogenicity island specific to CRC-associated SGG isolates. Most of these human-derived SGG isolates exhibit resistance to multiple antibiotics. Our findings also offer additional insights into multilocus sequence typing (MLST), capsular loci, and pilus organization. Analysis of the repertoire of surface proteins reveals high potential for binding and foraging complex polysaccharides. Finally, comparative genomics with the phylogenetically closest non-pathogenic subspecies S. gallolyticus subps. macedonicus, confirmed that SGG pathogenicity-associated factors mostly rely on a large repertoire of surface proteins involved in host colonization, presence of C5a peptidase to avoid innate immunity, bile salt hydrolase to persist in the gut, and of specific bacteriocin and type VII-dependent effectors to colonize the host colon. Additionally, the presence of extracellular polysaccharides in SGG probably helps the bacterium survive in harsher conditions. ImportanceStreptococcus gallolyticus subsp. gallolyticus (SGG) was the first intestinal bacterium associated with colorectal cancer. It is now widely accepted that colonic microbiota dysbiosis contributes to oncogenesis, with a higher relative abundance of several potentially pro-carcinogenic bacteria. For example, the oncogenic role of Escherichia coli pks+ and enterotoxinogenic Bacteroides fragilis in colorectal cancer have been well established identifying the role of genetic loci encoding toxins. Through the sequencing and analysis of 11 clinical SGG isolates from CRC patients and comparisons with non-CRC isolates, we uncovered a significant diversity among CRC-associated strains. Our findings suggest that SGG association with CRC is complex and is not linked to a specific strain or pathogenicity island, thus highlighting the opportunistic and versatile nature of SGG.

microbiology↗

bioRxiv2023

Transcriptome profiling of human colonic cells exposed to the gut pathobiont Streptococcus gallolyticus subsp. gallolyticus.

Streptococcus gallolyticus sp. gallolyticus (SGG) is a gut pathobiont involved in the development of colorectal cancer (CRC). To decipher the contribution of SGG in tumor initiation and/or acceleration respectively, a global transcriptome was performed in normal colonic cells (FHC) and in tumoral colonic cells (HT29). To identify SGG-specific alterations, we chose the phylogenetically closest relative, Streptococcus gallolyticus subsp. macedonicus (SGM) as the control bacterium. We show that SGM, a bacterium generally considered as safe, did not induce any transcriptional changes on the two human colonic cells. The transcriptional reprogramming induced by SGG was significantly different in FHC and HT29 cells, with most of the up- and down-regulated genes associated with cancer disease. Top up-regulated genes related to cancer were: (i) IL-20, CLK1, SORBS2, ERG1, PIM1, SNORD3A for normal FHC cells and (ii) TSLP, BHLHA15, LAMP3, ZNF27B, KRT17, ATF3 for cancerous HT29 cells. SGG induces much stronger transcriptional changes in cancerous than in normal colonic cells (2,090 vs 128 genes being affected, respectively). Gene set enrichment analysis reveals that SGG-induced strong ER- (endoplasmic reticulum) stress and UPR- (unfolded protein response) activation in colonic epithelial cells. Our results suggest that SGG induces a pro-tumoral shift in human colonic cells, particularly in transformed cells potentially accelerating tumor development in the colon.

microbiology↗

bioRxiv2022

Gallocin A, an atypical two-peptide bacteriocin secreted by Streptococcus gallolyticus subsp. gallolyticus

Streptococcus gallolyticus subsp. gallolyticus (SGG) is an opportunistic gut pathogen associated with colorectal cancer. We previously showed that colonization of the murine colon by SGG in tumoral conditions was strongly enhanced by the production of gallocin A, a two-peptide bacteriocin. Here, we aimed at characterizing the mechanisms of its action and resistance. Using a genetic approach, we demonstrated that gallocin A is composed of two peptides, GllA1 and GllA2, which are inactive alone and act together to kill "target" bacteria. We showed that gallocin A can kill phylogenetically close relatives. Importantly, we demonstrated that gallocin A peptides can insert into membranes and permeabilize lipid bilayer vesicles. Next, we showed that the third gene of the gallocin A operon named GIP, is necessary and sufficient to confer immunity to gallocin A. Structural modelling of GllA1 and GllA2 mature peptides suggested that both peptides form alpha-helical hairpins stabilized by intramolecular disulfide bridges. The presence of a disulfide bond in GllA1 and GllA2 was confirmed experimentally. Addition of disulfide reducing agents abrogated gallocin A activity. Likewise, deletion of a gene encoding a surface protein with a thioredoxin-like domain impaired gallocin A ability to kill Enterococcus faecalis. Structural modelling of GIP revealed a hairpin-like structure strongly resembling that of the GllA1 and GllA2 mature peptides, suggesting a mechanism of immunity by competition with GllA1/2. Finally, identification of other class IIb bacteriocins exhibiting a similar alpha-helical hairpin fold stabilized with an intramolecular disulfide bridge suggests the existence of a new subclass of class IIb bacteriocins. IMPORTANCEStreptococcus gallolyticus subsp. gallolyticus (SGG), previously named Streptococcus bovis biotype I, is an opportunistic pathogen responsible for invasive infections (septicemia, endocarditis) in elderly people and often associated with asymptomatic colon tumors. SGG is one of the first bacteria to be associated with the occurrence of colorectal cancer in humans. Previously, we showed that tumor-associated conditions in the colon provide to SGG with the ideal environment to proliferate at the expense of phylogenetically and metabolically closely related commensal bacteria such as enterococci (Aymeric et al., 2017). SGG takes advantage of CRC-associated conditions to outcompete and substitute commensal members of the gut microbiota using a specific bacteriocin named gallocin and renamed gallocin A recently following the discovery of gallocin D in a peculiar SGG isolate. Here, we showed that gallocin A is a two-peptide bacteriocin and that both GllA1 and GllA2 peptides are required for antimicrobial activity. Gallocin A was shown to permeabilize bacterial membranes and to kill phylogenetically closely related bacteria such as most streptococci, lactococci and enterococci, probably through membrane pore formation. GllA1 and GllA2 secreted peptides are unusually long (42 and 60 amino acids long) and with very few charged amino acids compared to well-known class IIb bacteriocins. In silico modelling revealed that both GllA1 and GllA2 exhibit a similar hairpin-like conformation stabilized by an intramolecular disulfide bond. We also showed that the GIP immunity peptide also forms a hairpin like structure like GllA1/GllA2. Thus, we hypothesize that GIP blocks the formation of the GllA1/GllA2 complex by interacting with GllA1 or GllA2. Gallocin A may constitute the first class IIb bacteriocin displaying disulfide bridges important for its structure and activity and the founding member of a subtype of class IIb bacteriocins.

microbiology↗

bioRxiv2020

Bacteriocin production in Streptococcus gallolyticus by a complex 4-component regulatory system with activator and anti-activator activities

Bacteriocins are natural antimicrobial peptides produced by bacteria to kill closely related competitors. The opportunistic pathogen Streptococcus gallolyticus (Sgg) was recently shown to outcompete commensal enterococci of the murine microbiota in tumoral conditions thanks to the production of a two-peptide bacteriocin named gallocin. We here identified 4 genes involved in the regulatory control of gallocin in Sgg UCN34, respectively encoding a histidine kinase/response regulator two-component system (BlpH/BlpR), a secreted peptide (GSP), and a putative regulator of unknown function (BlpS). While BlpR is a typical 243-aa response regulator possessing a phospho-receiver domain and a LytTR DNA-binding domain, BlpS is a 108-aa protein containing only a LytTR domain. Our results showed that the secreted peptide GSP activates the dedicated two-component system BlpH/BlpR to induce gallocin transcription. A genome-wide transcriptome analysis indicates that this regulatory system (GSP-BlpH/BlpR) is highly specific for bacteriocin production. Importantly, as opposed to BlpR, BlpS was shown to repress gallocin gene transcription. A conserved operator DNA sequence of 30-bp was found in all promoter regions regulated by BlpR and BlpS. EMSA assays showed direct and specific binding of the two gallocin regulators to various regulated promoter regions in a dose dependent manner. Gallocin expression appears tightly controlled in Sgg by quorum sensing and antagonistic activity of 2 LytTR-containing proteins. SignificanceStreptococcus gallolyticus (Sgg), formely known as S. bovis biotype I, is an opportunistic pathogen causing septicemia and endocarditis in the elderly often associated with asymptomatic colonic neoplasia. We previously showed that Sgg produces a bacteriocin, termed gallocin, enabling colonization of the colon in tumoral conditions by outcompeting commensal members of the gut. Here we characterized a 4-component regulatory system that regulates gallocin transcription, which is activated by the response regulator BlpR. BlpR itself is activated by a quorum sensing peptide GSP and a dedicated histidine kinase BlpH. Interestingly, BlpS, a small DNA-binding protein co-transcribed with BlpR was found to repress gallocin genes transcription, likely by antagonizing BlpR. Understanding gallocin regulation is crucial to prevent Sgg colon colonization in tumoral conditions.

microbiology↗

bioRxiv2019

Heterogeneous expression of Pil3 pilus is critical for Streptococcus gallolyticus translocation across polarized colonic epithelial monolayers

Streptococcus gallolyticus subspecies gallolyticus (Sgg) is an opportunistic pathogen responsible for septicaemia and endocarditis in elderly persons. Sgg is also a commensal of the human gastrointestinal tract. Here we demonstrate that Sgg strain UCN34 translocates across tight intestinal barriers in vitro in a Pil3-dependent manner. Confocal images of UCN34 passage across human colonic cells reveals that Sgg utilizes a paracellular pathway. Pil3 was previously shown to be expressed heterogeneously and WT UCN34 consists of about 90% of Pil3low and 10% of Pil3high cells. We found that both the {Delta}pil3 mutant and the Pil3+ overexpressing variant could not translocate across Caco-2 and T84 barriers. Interestingly, combining live {Delta}pil3 mutant cells with fixed Pil3+ variants in a 10:1 ratio (mimicking UCN34 WT population) allowed efficient translocation of the {Delta}pil3 mutant. These experiments demonstrate that heterogeneous expression of Pil3 plays a key role in optimal translocation of Sgg across the intestinal barrier.\n\nABSTRACT IMPORTANCEStreptococcus gallolyticus subsp. gallolyticus (Sgg) is an opportunistic pathogen responsible for septicemia and infective endocarditis in elderly persons. Sgg is a commensal of the rumen of herbivores and transmission to humans most probably occurs through the oral route. In this work, we have studied how this bacterium crosses the intestinal barrier using well-known in vitro models. Confocal microscopy images revealed that Sgg UCN34 can traverse the epithelial monolayer in between adjacent cells. We next showed that passage of Sgg from the apical to the basolateral compartment is dependent on the heterogenous expression of the Pil3 pilus at the bacterial surface. We hypothesize that Pil3high cocci adhere firmly to epithelial cells to activate transient opening of tight junctions thereby allowing the traversal of Pil3low bacteria.

microbiology↗