Biology subjects

Morvan, C.

Publications and source records attributed to Morvan, C..

3 recordsLinked to original sources

bioRxiv2023

The multiplicity of Thioredoxin systems meets the specific needs of Clostridia

Oxidative stress is a highly common stress for cells, which targets proteins with oxidation of cysteine residues. The thioredoxin (Trx) system, which is a ubiquitous system for thiol- and protein-repair, is composed of a thioredoxin (TrxA) and a thioredoxin-reductase (TrxB). TrxAs reduce disulfide bonds of oxidized proteins and are then usually recycled by a single pleiotropic NAD(P)H-dependent TrxB (NTR). However, some Clostridia have also ferredoxin-dependent TrxBs. In this work, we first analyzed the composition of Trx systems across Bacteria. Most of bacteria have only one NTR, but organisms in some Phyla including Firmicutes have several TrxBs. In Firmicutes, this multiplicity of TrxBs is observed only in Clostridia. We thus used Clostridioides difficile as a model to investigate the biological relevance of TrxB multiplicity by studying the physiological roles of the Trx systems in this gut pathogen. Three TrxAs and three TrxBs are present in the 630{Delta}erm strain. We showed that two systems were involved in response to infection-related stresses, allowing survival of vegetative cells to exposure to oxygen, inflammation-related molecules and bile salts. A supplementary TrxB copy present in some C. difficile strains also contributes to this stress-response arsenal. One of the conserved stress-response Trx system was also found to be present in the spore via a dual transcriptional control by different sigma factors. This system contributes to spore survival to hypochlorite and ensure proper germination in the presence of oxygen. Finally, we found that the third Trx system was contributing to sporulation. This involvement was likely linked to the recycling of the glycine-reductase, a Stickland pathway enzyme that allows consumption of glycine, a spore co-germinant. Altogether, our results showed that the multiplicity of Trx systems produced under the control of different regulatory signals and networks and the diversity of TrxBs meet specific needs of Clostridia, i.e., adaptation to strong stress exposure, sporulation and Stickland pathways. More broadly, this multiplicity responds to cell compartmentation and differentiation, which can be transposed to other multiple-TrxBs organisms such as Cyanobacteria or eukaryotes.

microbiology↗

bioRxiv2022

6S RNA-dependent antibiotic susceptibility

Bacterial small RNAs (sRNAs) contribute to a variety of regulatory mechanisms that modulate wide ranging pathways, including metabolism, virulence, and antibiotic resistance. We investigated the involvement of sRNAs in rifampicin resistance in the opportunistic pathogen Staphylococcus aureus. Using a competition assay with an sRNA mutant library, we identified 6S RNA as being required for protection against low concentrations of rifampicin, an RNA polymerase (RNAP) inhibitor. This effect applied to rifabutin and fidaxomicin, two other RNAP-targeting antibiotics. 6S RNA is highly conserved in bacteria and its absence in two other major pathogens, Salmonella enterica and Clostridioides difficile, also impaired susceptibility to RNAP inhibitors. In S. aureus, 6S RNA is produced from an autonomous gene and accumulates in stationary phase. In contrast to what was reported in Escherichia coli, S. aureus 6S RNA does not appear to play a critical role in the transition from exponential to stationary phase, but affects {sigma}B-regulated expression in prolonged stationary phase. Nevertheless, its protective effect against rifampicin is independent of alternative sigma factor {sigma}B activity. Our results suggest that 6S RNA helps maintain RNAP-{sigma}A integrity in S. aureus, which could in turn help bacteria withstand low concentrations of RNAP inhibitors.

microbiology↗

bioRxiv2019

Permissive Fatty Acid Incorporation in Host Environments Promotes Staphylococcal Adaptation to FASII Antibiotics

Development of fatty acid synthesis pathway (FASII) inhibitors against the major human pathogen Staphylococcus aureus hinges on the accepted but unproven postulate that an endogenously synthesized branched chain fatty acid is required to complete membrane phospholipids. Evidence for anti-FASII efficacy in animal models supported this view. However, restricted test conditions used previously to show FASII antibiotic efficacy led us to investigate these questions in a broader, host-relevant context. We report that S. aureus rapidly adapts to FASII antibiotics without FASII mutations when exposed to host environments. Treatment with a lead FASII antibiotic upon signs of infection, rather than just after inoculation as commonly practiced, failed to eliminate S. aureus from infected organs in a septicemia model. In vitro, addition of serum facilitated rapid S. aureus FASII bypass by environmental fatty acid (eFA) replacement in phospholipids. Serum lowers membrane stress, leading to increased retention of the two substrates required for exogenous fatty acid (eFA) utilization. In these conditions, eFA occupy both phospholipid positions 1 and 2, regardless of anti-FASII selection. This study revises conclusions on S. aureus fatty acid requirements by disproving the postulate of fatty acid stringency, and reveals an Achilles heel for using FASII antibiotics to treat infection in monotherapy.\n\nSignificance statementAntibiotic discovery to overcome treatment failure has huge socio-medical and economic stakes. The fatty acid synthesis (FASII) pathway is considered an ideal druggable target against the human pathogen Staphylococcus aureus, based on evidence of anti-FASII efficacy in infection models, and the postulate that S. aureus synthesizes an irreplaceable fatty acid. We report that S. aureus alters its behavior in host-relevant conditions. Administering FASII antibiotics upon signs of infection, rather than just after inoculation as frequently practiced, failed to clear septicemic infections. In serum, S. aureus rapidly overcomes FASII antibiotics by incorporating alternative fatty acids. We conclude that previously, premature antibiotic treatments and experimental constraints masked S. aureus antibiotic adaptation capacity. These findings should help streamline future drug development programs.

microbiology↗