Biology subjects

Chauvat, F.

Publications and source records attributed to Chauvat, F..

5 recordsLinked to original sources

bioRxiv2026

Copper-Mediated Antimicrobial Activity : Targeting Cytochrome c Complexes Across Bacterial Species

Copper (Cu) exerts potent antibacterial activity and contributes to mammalian immune defense. Although solvent exposed 4Fe-4S clusters in cytoplasmic dehydrogenases are major intracellular targets of Cu, its chemical reactivity and subcellular distribution suggest that additional cellular processes may be vulnerable to Cu toxicity. Here, we identify c-type cytochrome biogenesis as a conserved target of Cu excess across diverse pathogenic and environmental bacteria. Analysis of respiratory membrane complexes from pathogens, including Vibrio cholerae and Pseudomonas aeruginosa, revealed pronounced and selective sensitivity of c-type cytochrome-containing complexes to excess Cu. In P. aeruginosa, elevated Cu impaired the cbb3-type cytochrome c oxidase and NapBC-containing cytochrome c complexes while largely sparing complexes independent of c-type cytochromes, including the aa3-type cytochrome c oxidase and succinate dehydrogenase. In contrast, the caa3-type cytochrome c oxidase of Bacillus subtilis, which contains a covalently bound cytochrome c subunit, was also severely affected. Cu likewise depleted c-type cytochromes in plant-associated and photosynthetic bacteria, indicating that this vulnerability is broadly conserved. Complementary analyses in B. subtilis and Escherichia coli showed that Cu primarily disrupts c-type cytochrome assembly rather than promoting the degradation of preassembled complexes. These findings establish c-type cytochrome-containing respiratory complexes as conserved targets of Cu toxicity. Given their central role in electron transport and adaptation to oxygen-limited environments, disruption of cytochrome c biogenesis may contribute to Cu antimicrobial activity and expose a potential vulnerability in pathogens that rely on c-type cytochromes for microaerobic respiration and colonization of hypoxic host tissues.

microbiology↗

bioRxiv2026

MnSOD Diversifies, while FeSOD Dominates Superoxide Defense in Cyanobacteria

Cyanobacteria are unique among prokaryotes in possessing photosynthetic thylakoid membranes enclosing an internal lumen, where superoxide production is expected to be substantial. Thylakoid-associated superoxide dismutases (SODs) would seem the obvious first line of defense, yet many cyanobacteria rely instead on a single soluble cytoplasmic enzyme, raising the question of what role thylakoid-associated SOD isoforms actually play. Using Cyanothece sp. PCC 7425, which encodes both a cytoplasmic FeSOD and a thylakoid-associated MnSOD, we combined sequence analysis, structural, genetics, and biochemical approaches to characterise FeSOD and MnSOD cellular localisation and assess each enzyme's contribution to superoxide defense. Cyanobacterial MnSODs display diverse N-terminal architectures, consistent with soluble, transmembrane, or lipid-anchored forms, yet contribute only modestly to superoxide defense in Cyanothece PCC 7425 and, very likely, across cyanobacteria broadly. Soluble FeSOD instead provides the major line of defense, showing that thylakoid association does not guarantee physiological importance. This predominance of a cytoplasmic enzyme highlights the central role of cytoplasmic superoxide detoxification, consistent with superoxide being generated mainly at the PSI acceptor side, and extends to the chloroplast stroma of plants. Our findings support a model in which SOD distribution reflects metal availability, enzyme properties, and subcellular organisation : FeSOD protects the compartment harbouring the main targets of PSI-associated superoxide, whereas MnSOD is retained where thylakoid association offers additional local protection, but becomes dispensable when the local ROS burden is limited. Spatial matching between superoxide production, antioxidant localisation, and target vulnerability may thus shape the diversification and maintenance of antioxidant systems across cyanobacteria and chloroplasts.

microbiology↗

bioRxiv2026

Targeted genome editing of the non-model cyanobacterium Cyanothece PCC 7425 via CRISPR/Cas12a

Cyanobacteria are diverse photosynthetic microorganisms of great interest for fundamental science and sustainable biotechnological applications. However, their polyploidy makes genetic manipulation challenging and time-consuming. The development of CRISPR/Cas tools has greatly accelerated genome editing and metabolic engineering of few cyanobacterial model species. In this work, we extend the CRISPR/Cas12a system for targeted gene deletion in the non-model cyanobacterium Cyanothece PCC 7425, interesting for its ability to perform intracellular calcium carbonate (CaCO3) biomineralization, nitrogen fixation, etc. We demonstrate for the first time its tractability to gene knockout by generating deletion mutants of four genes (cax3-cax4, gor, and sodB) acting in metabolism and/or response to stresses, using Cas12a mediated homologous recombination. Importantly, full chromosome segregation was rapidly achieved after a single round of selection in all cases. All mutants were genotypically and phenotypically characterised. Moreover, biochemical analysis in the case of{Delta} sodB mutant further confirmed its targeted deletion. Overall, CRISRPR/Cas12a provides a rapid and efficient system for genome editing in Cyanothece PCC 7425, establishing this organism as a versatile model for studying oxidative stress pathways, metal toxicity and moreover, the still poorly known mechanism(s) of intracellular CaCO3 biomineralization. Key PointsO_LIRapid and efficient CRISPR/Cas12a editing established in Cyanothece PCC 7425. C_LIO_LIFully segregated knockout mutants obtained after single selection round. C_LIO_LIPlatform for nuclear waste bioremediation and other biotechnological applications. C_LI

microbiology↗

bioRxiv2025

Acclimation of photosynthesis began with a Cu-binding superoxide detoxifying enzyme

Plant acclimation is a growing scientific concept, at molecular, cellular and global scales. All photosynthetic organisms that created an oxic atmosphere on earth possess a gene of unknown function "Acclimation of Photosynthesis to the Environment 1". Here we show that APE1 encodes a thylakoid-bound protein with a unique motif that binds copper and detoxifies the superoxide anion radical, O2*-. Maturation of the recombinant APE1 protein from Chlamydomonas reinhardtii requires formation of cysteine disulfide bonds after copper binding or via a high affinity interaction with a copper chaperone (Plastid Copper Chaperone 1) that boosts its scavenging capacity for O2*-. APE1 co-occurs in evolution with Photosystem II oxygen evolving proteins and it is the archaic O2*- detoxifying enzyme for acclimating photosynthesis to an oxygenic environment.

plant biology↗

bioRxiv2021

A new gene family diagnostic for intracellular biomineralization of amorphous Ca-carbonates by cyanobacteria

Cyanobacteria have massively contributed to carbonate deposit formation over the geological history. They are traditionally thought to biomineralize CaCO3 extracellularly as an indirect byproduct of photosynthesis. However, the recent discovery of freshwater cyanobacteria forming intracellular amorphous calcium carbonates (iACC) challenges this view. Despite the geochemical interest of such a biomineralization process, its molecular mechanisms and evolutionary history remain elusive. Here, using comparative genomics, we identify a new gene (ccyA) and protein (calcyanin) family specifically associated with cyanobacterial iACC biomineralization. Calcyanin is composed of a conserved C-terminal domain, which likely adopts an original fold, and a variable N-terminal domain whose structure allows differentiating 4 major types among the 35 known calcyanin homologues. Calcyanin lacks detectable full-length homologs with known function. Yet, genetic and comparative genomic analyses suggest a possible involvement in Ca homeostasis, making this gene family a particularly interesting target for future functional studies. Whatever its function, this new gene family appears as a gene diagnostic of intracellular calcification in cyanobacteria. By searching for ccyA in publicly available genomes, we identified 13 additional cyanobacterial strains forming iACC. This significantly extends our knowledge about the phylogenetic and environmental distribution of cyanobacterial iACC biomineralization, especially with the detection of multicellular genera as well as a marine species. Phylogenetic analyses indicate that iACC biomineralization is ancient, with independent losses in various lineages and some HGT cases that resulted in the broad but patchy distribution of calcyanin across modern cyanobacteria. Overall, iACC biomineralization emerges as a new case of genetically controlled biomineralization in bacteria. Significance statementFew freshwater species of Cyanobacteria have been known to mineralize amorphous CaCO3 (ACC) intracellularly. Despite the geochemical interest of this biomineralization, its evolutionary history and molecular mechanism remain poorly known. Here, we report the discovery of a new gene family that has no homolog with known function, which proves to be a good diagnostic marker of this process. It allowed to find cyanobacteria in several phyla and environments such as seawater, where ACC biomineralization had not been reported before. Moreover, this gene is ancient and was independently lost in various lineages with some later horizontal transfers, resulting in a broad and patchy phylogenetic distribution in modern cyanobacteria.

evolutionary biology↗