Biology subjects

Couzon, F.

Publications and source records attributed to Couzon, F..

6 recordsLinked to original sources

bioRxiv2025

Quorum sensing dependent repression of the Staphylococcus aureus transcription termination factor Rho is necessary for pathogenicity

In Staphylococcus aureus, the transcription termination Rho factor has been identified as an attenuator of virulence, highlighting this universal protein as a new player in S. aureus pathophysiology. Moreover, Rho is required for the repression of "pervasive" transcription, which results from transcription at cryptic promoters or from transcriptional readthrough. In our study, we demonstrated that the rho transcript is specifically repressed by the quorum sensing-dependent RNAIII during the stationary phase of growth, allowing exotoxins to be activated at this stage. Rho-dependent RNA targets were identified using RIP-seq and differential transcriptomic analyses, revealing that several of these targets are involved in adhesion, dissemination, and the host responses. Our data provide a molecular explanation for the functions of this well-conserved termination factor, which have evolved in this human pathogen.

microbiology↗

bioRxiv2023

RlmQ: A Newly Discovered rRNA Modification Enzyme Bridging RNA Modification and Virulence Traits in Staphylococcus aureus

rRNA modifications play crucial roles in fine-tuning the delicate balance between translation speed and accuracy, yet the underlying mechanisms remain elusive. Comparative analysis of the ribosomal RNA modifications in taxonomically distant bacteria could help define their general as well as species-specific roles. In this study, we identified a new methyltransferase, RlmQ, in Staphylococcus aureus responsible for the Gram-positive specific m7G2601, which is not modified in E. coli (G2574). We also demonstrate the absence of methylation on C1989, equivalent to E. coli C1962, which is methylated at position 5 by the Gram-negative specific RlmI methyltransferase, a paralogue of RlmQ. Both modifications (S. aureus m7G2601 and E. coli m5C1962) are situated within the same tRNA accommodation corridor, hinting at a potential shared function in translation. Inactivation of S. aureus rlmQ causes the loss of methylation at G2601 and significantly impacts growth, cytotoxicity, and biofilm formation. These findings unravel the intricate connections between rRNA modifications, translation, and virulence in pathogenic Gram-positive bacteria.

molecular biology↗

bioRxiv2022

Complex regulation of gamma-hemolysin expression impacts S. aureus virulence

Staphylococcus aureus gamma-hemolysin CB (HlgCB) is a core-genome encoded pore-forming toxin that targets the C5a receptor, similarly as the phage-encoded Panton-Valentine Leucocidin. Absolute quantification by mass spectrometry of HlgCB in 39 community-acquired pneumonia (CAP) isolates showed considerable variations in HlgC and HlgB yields between isolates. Interestingly, when testing the hypothesis that HlgCB might be associated with severe S. aureus CAP, we found that a high level of HlgCB synthesis was associated with mortality in a rabbit model of pneumonia. To decipher the molecular basis for the variation in hlgCB and hlgB expression and protein production among strains, different regulation levels were analyzed in representative clinical isolates and reference strains. Although HlgC and HlgB are encoded on a single operon, their levels were dissociated in 10% of the clinical strains studied. HlgCB amount and HlgC/HlgB ratio were found to both depend on promotor activity, mRNA stability and translatability, and on the presence of an individual hlgB mRNA processed from the hlgCB transcript. Strikingly, toe-printing and in vitro translation assays revealed that a single SNP in the 5-UTR of hlgCB mRNA strongly impaired hlgC translation in the USA300 strain, leading to a strong decrease in HlgC but not in HlgB; the level of HlgB is likely to have been maintained by the presence of the processed hlgB mRNA. This work illustrates the complexity of virulence factor expression in clinical strains and demonstrates a butterfly effect, where subtle genomic variations have a major impact on phenotype and virulence. Author SummaryThe Gram-positive bacterium Staphylococcus aureus can provoke a wide range of infections due to its ability to produce a large diversity of virulence factors, including immune evasion molecules, adhesins, and toxins. Some of these toxin-encoding genes are localized in mobile genetic elements, and are thus not present in all strains, whilst others are encoded in the core-genome and present in all strains. Gamma-hemolysin CB is a core-genome encoded toxin but its amount varies between community-acquired pneumonia isolates. The regulation mechanisms underlying this variation however, are not well characterized. Here, we show that gamma-hemolysin expression levels vary largely among clinical strains and that, when highly produced, it induces high mortality in a rabbit model of pneumonia. The molecular basis for the variation in gamma-hemolysin expression depends on multiple mechanisms including promoter strength, transcript stability and processing, and translatability (i.e. the amount of protein that is synthetized by the ribosome for a given transcript). Incredibly, all these factors rely on a subtle genetic modification. This work emphasizes the importance of the disparity in virulence factor expression among clinical isolates and points the extreme complexity of the molecular mechanisms underlying their regulation, rendering the prediction of virulence for a clinical isolate difficult.

microbiology↗

bioRxiv2022

Staphylococcus aureus virulence factor expression matters: input from targeted proteomics shows Panton-Valentine leucocidin impact on mortality

In the case of commensal bacteria such as Staphylococcus aureus, the transition from commensalism to invasion and disease as well as disease severity in the course of an infection remain poorly predictable on the sole basis of virulence gene content. To determine whether variations in the levels of expression of the numerous S. aureus virulence factors could affect disease occurrence and/or severity, we developed a targeted proteomic approach that monitored 149 peptide surrogates targeting 44 proteins. Semi-quantification was achieved by normalization on the signal of ribosomal proteins. We then evaluated this approach on a series of S.aureus strains from 136 patients presenting a severe community-acquired pneumonia, all admitted to an intensive care unit. After adjusting to the Charlson Comorbidity Index score the multivariate analysis of severity parameters found that HlgB, Nuc, and Tsst-1 were positively associated while BlaI and HlgC were negatively associated with leucopenia. BlaZ and HlgB were positively associated with hemoptysis and HlgC was negatively associated with hemoptysis. Regarding mortality, both the multivariate (1.28; 95%CI[1.02;1.60]) and survival (1.15; 95%CI[1.016;1.302]) analyses showed that only PVL was associated with death in a dose-dependent manner. Beyond highlighting the decisive role of PVL in community-acquired pneumonia severity, this study brings the proof of concept that "expression matters" and proposes a method that can be routinely implemented in laboratories, for any Staphylococcal disease, and which could be developed for other commensal bacteria. One Sentence SummaryA highly multiplexed semi-quantitative mass spectrometry method was developed for 44 Staphylococcus aureus virulence factors; applied to a 136-strain collection from severe community-acquired pneumonia patients, it showed that Panton-Valentine leucocidin was the only factor to impact mortality in a dose-dependent manner.

microbiology↗

bioRxiv2022

All Staphylococcus aureus bacteraemia strains have the potential to cause infective endocarditis: results of GWAS and experimental animal studies

Abstract and KeywordsO_ST_ABSAimsC_ST_ABSInfective endocarditis (IE) complicates 10-20% of Staphylococcus aureus bacteraemia (SAB). We aimed to determine whether IE strains of S. aureus are genotypically different or behave differently in experimental endocarditis models as compared to non-IE SAB strains. Methods and ResultsWe conducted a genome wide association study (GWAS) of 924 S. aureus genomes from IE (274) and non-IE (650) SAB patients, and tested a subset of strains in two experimental animal models of IE, one studying the early step of bacterial adhesion to inflamed mice valves, the second evaluating the local and systemic developmental process of IE on mechanically damaged rabbit valves. The genetic profile of S. aureus IE and non-IE SAB strains did not differ when considering single nucleotide polymorphisms, coding sequences and k-mers analyses in GWASs. In the inflammation-induced IE model in mice no difference was observed between IE and non-IE SAB strains both in adhesion to the cardiac valves and in the propensity to cause IE; in the mechanical IE-induced rabbit model, there was no difference between IE and non-IE SAB strains regarding vegetation size and CFU. ConclusionS. aureus isolates from SAB patients with and without IE were indistinguishable, by GWAS and by two in vivo models of IE. Thus, S. aureus strain variation is not the primary determinant of IE. Pending the possible identification of host factors predisposing to IE, all strains of S. aureus must be considered in patients as capable of causing this common, lethal infection once they have accessed the bloodstream. Translational PerspectiveStaphylococcus aureus endocarditis (IE) is a deadly complication of S. aureus bacteraemia (SAB). Beyond well-identified host related IE risk factors, whether bacterial features may influence the occurrence of IE in the course of bacteraemia remain elusive. We analysed the genomes of 924 S. aureus strains from IE and non-IE SAB and compared some in two in vivo IE models. We demonstrated that the propensity of S. aureus to cause IE in the course of bacteraemia does not depend on the intrinsic genetic or virulence factors of S. aureus. These findings are of importance for the management of S. aureus bacteraemia.

microbiology↗

bioRxiv2020

Potential role of Mercury pollutants in the success of Methicillin-Resistant Staphylococcus aureus USA300 in Latin America

Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) lineage known as USA300-North American (NA) has become highly prevalent in North America whilst a USA300 variant known as USA300-LV, harboring a mercury resistance element (COMER), has become dominant in South America. We investigated whether mercury pollution, which is common in South America notably because of artisanal gold mining, may explain the local dominance pattern of USA300-LV. Density-based estimation of epidemic success in 250 genomes of the ST8 lineage revealed that the acquisition of COMER in USA300 progenitors increased success in South American countries but decreased success elsewhere. The fitness of USA300-LV was impaired in vitro compared with USA300-NA, but the addition of sub-inhibitory concentration of mercury provided a strong fitness advantage to USA300-LV and triggered an overexpression of major virulence factors. The success of USA300-LV in South America may result from low-level mercury exposure selecting resistant and virulent strains.

microbiology↗