Biology subjects

Laffont, C.

Publications and source records attributed to Laffont, C..

6 recordsLinked to original sources

bioRxiv2026

Utilization of cyanobacterial siderophore cyanochelin B by phylogenetically distant heterotrophs suggest its role in mediating microbial interactions

Cyanobacteria are key prokaryotic primary producers in diverse ecosystems, yet the role of cyanobacterial siderophores in shaping their associated microbiomes remains unexplored. Our study demonstrates the benefits provided to the heterotrophic co-habitants of filamentous cyanobacteria in terrestrial microbial biofilms, focusing on the recently discovered widespread siderophores cyanochelins. To address the acceptance of cyanochelin B (CychB) across multiple bacterial classes, we first investigated its role in providing iron to a model siderophore producer P. aeruginosa PAO1 and selected Pseudomonas natural isolates, which were found to utilize CychB under iron limiting conditions while downregulating endogenous siderophore production. In response to CychB, PAO1 expresses a siderophore internalization cluster, which is localized in multiple Pseudomonas natural isolates. Using metagenome analysis, we characterized the bacterial community recruited along with CychB producing Phormidesmis cyanobacteria under long-term iron starvation. Potential CychB acceptor bacteria associated with the CychB producer were predominantly lacking endogenous siderophore machineries. Using siderophore selective pressure, we isolated a genuine CychB acceptor, gram-negative bacterium Methyloversatilis sp. S146 and demonstrated that its genome hosts an iron processing cluster overexpressed after CychB feeding, recognizing Methyloversatilis as a candidate for further mechanistic investigation of iron acquisition-driven microbial interactions. Our results indicate that CychB supports a specific subset of co-habiting heterotrophic bacteria during iron starvation, further emphasizing the role of cyanobacteria as key drivers of nutrient flows within globally important microbial soil crust ecosystems, supporting microbial life in nutrient-limited environments. These findings provide a mechanistic foundation to elucidate the role of cyanochelins as a public good in these communities.

microbiology↗

bioRxiv2025

Pseudogenization of the cntQ permease confers distinct yersinopine-metal uptake selectivity in Yersinia species

Yersinopine, a nicotianamine-like metallophore, was recently identified through biochemical analyses, but its in vivo production and functional role remain uncharacterized. In Yersinia pseudotuberculosis and its recent descendant Yersinia pestis, the cnt operon (cntPQRLMI) putatively encodes the biosynthesis and transport of yersinopine. In Y. pestis, however, two frameshift mutations disrupt cntQ, which encodes the predicted permease for yersinopine-metal complexes. This pseudogenization raises critical questions about the functional relevance of yersinopine in these closely related species. Here, we show that cnt operon expression is repressed by the zinc uptake regulator Zur and that both Y. pestis and Y. pseudotuberculosis secrete yersinopine under zinc-limited conditions. Unexpectedly, the operon mediates iron uptake in Y. pseudotuberculosis but supports zinc acquisition in Y. pestis. Moreover, targeted disruption of cntQ in Y. pseudotuberculosis shifts metal specificity from iron to zinc, mimicking the Y. pestis phenotype. Collectively, our results suggest that a single pseudogenization event could rewire metal uptake specificity. Our findings illustrate how evolutionary genome reduction can reshape bacterial physiology.

microbiology↗

bioRxiv2024

Interactions between Pseudomonas aeruginosa and six opportunistic pathogens cover a broad spectrum from mutualism to antagonism

Bacterial infections often involve more than one pathogen. While it is known that polymicrobial infections can impact disease outcomes, we have a poor understanding about how pathogens affect each others behaviour and fitness. Here, we used a microscopy approach to explore interactions between Pseudomonas aeruginosa and six opportunistic human pathogens that often co-occur in polymicrobial infections: Acinetobacter baumannii, Burkholderia cenocepacia, Escherichia coli, Enterococcus faecium, Klebsiella pneumoniae, and Staphylococcus aureus. When following growing micro-colonies on agarose pads over time, we observed a broad spectrum of species-specific ecological interactions, ranging from mutualism to antagonism. For example, P. aeruginosa engaged in a mutually beneficial interaction with E. faecium but suffered from antagonism by E. coli and K. pneumoniae. While we found little evidence for active directional growth towards or away from cohabitants, we observed that certain species increased growth in double layers in co-cultures and that physical forces due to fast colony expansion had a major impact on fitness and interaction patterns. Overall, our work provides an atlas of pathogen interactions, potentially useful to understand species dynamics in polymicrobial infections. We discuss possible mechanisms driving pathogen interactions and offer predictions of how the different ecological interactions could affect virulence.

microbiology↗

bioRxiv2023

RNAseq reveals that Pseudomonas aeruginosa mounts medium-dependent competitive responses when sensing diffusible cues from Burkholderia cenocepacia

Most habitats host diverse bacterial communities, offering opportunities for inter-species interactions. While competition might often dominate such interactions, little is known about whether bacteria can sense competitors and mount adequate responses. The competition-sensing hypothesis proposes that bacteria can use cues such as nutrient stress and cell damage to prepare for battle. Here, we tested this hypothesis by measuring transcriptome changes in Pseudomonas aeruginosa exposed to the supernatant of its competitor Burkholderia cenocepacia. We found that P. aeruginosa exhibited significant and growth-medium-dependent transcriptome changes in response to competition. In iron-rich medium, P. aeruginosa up-regulated genes encoding the type-VI secretion system and the siderophore pyoverdine, whereas genes encoding phenazine toxins and hydrogen cyanide were upregulated under iron-limited conditions. Moreover, general stress response and quorum-sensing regulators were upregulated upon supernatant exposure. Altogether, our results reveal nuanced competitive responses of P. aeruginosa when confronted with B. cenocepacia supernatant, integrating both environmental and social cues.

microbiology↗

bioRxiv2020

Involvement of the Pseudomonas aeruginosa MexAB-OprM efflux pump in the secretion of the metallophore pseudopaline

The ability for all organisms to acquire metals from their environment is essential for life. To overcome the metal restriction imposed by the hosts nutritional immunity, bacterial pathogens exploits the use of small high metal affinity molecules called metallophores. Metallophores are first synthetized in the cytoplasm, then secreted into the medium where they sequester the metal. The metal-metallophore complex is then imported into the bacterium following binding to dedicated cell surface receptors. Recently, a new family of metallophores has been discovered in pathogenic bacteria called staphylopine in Staphylococcus aureus and pseudopaline in Pseudomonas aeruginosa. Here, we are expending the molecular understanding of pseudopaline secretion/recovery cycle across the double-membraned envelope of the Gram-negative bacterium Pseudomonas aeruginosa. We first revealed that pseudopaline is secreted in a two-step process including export across the inner membrane by the CntI exporter followed by a specific transport across the outer membrane by the MexAB-OprM efflux pump. Such involvement of MexAB-OprM in pseudopaline secretion, reveal a new natural function that extends its spectrum of functions and therefore reasserts its interest as antibacterial target. We then addressed the fate of the recovered metal-loaded pseudopaline by combining in vitro reconstitution experiments using radio-labeled pseudopaline subjected to bacterial lysates, and in vivo phenotyping in absence of pseudopaline transporters. Our data support the existence of a pseudopaline degradation/modification mechanism, possibly involved in metal release following pseudopaline recovery. All together our data allowed us to provide an improved molecular model of secretion, recovery and fate of this important metallophore by P. aeruginosa. IMPORTANCEPseudopaline is a broad spectrum metallophore produced and used by Pseudomonas aeruginosa to supply the bacterium in metal in metal scarce environments. Here we are investigating the pseudopaline transport/recovery cycle across the bacterial envelope. We are first demonstrating that pseudopaline secretion in the medium is achieved by a specific efflux pump, usually dedicated to the release of toxic compounds such as antibiotics, thus revealing a new natural function for this efflux pump reasserting its interest as antibacterial target. Additional experiments also revealing the existence of an intracellular pseudopaline degradation mechanism providing new clues to another obscure step of the pseudopaline cycle which is the intracellular metal liberation from the imported metal-pseudopaline complex. All together our data allowed us to disclose important aspects of the secretion, recovery and fate of this essential molecule used by P. aeruginosa to survive during infections thus constituting new potential targets for antibacterial development.

microbiology↗

bioRxiv2019

Simple rules govern the diversity of bacterial nicotianamine-like metallophores

In metal-scarce environments, some pathogenic bacteria produce opine-type metallophores mainly to face the hosts nutritional immunity. This is the case of staphylopine, pseudopaline and yersinopine, identified in Staphylococcus aureus, Pseudomonas aeruginosa and Yersinia pestis respectively. These metallophores are synthesized by two (CntLM) or three enzymes (CntKLM), CntM catalyzing the last step of biosynthesis using diverse substrates (pyruvate or -ketoglutarate), pathway intermediates (xNA or yNA) and cofactors (NADH or NADPH), depending on the species. Here, we explored substrate specificity of CntM by combining bioinformatics and structural analysis with chemical synthesis and enzymatic studies. We found that NAD(P)H selectivity was mainly due to the amino acid at position 33 (S. aureus numbering) which ensures a preferential binding to NADPH when it is an arginine. Moreover, whereas CntM from P. aeruginosa preferentially uses yNA over xNA, the staphylococcal enzyme is not stereospecific. Most importantly, selectivity towards -ketoacids is largely governed by a single residue at position 150 of CntM (S. aureus numbering): an aspartate at this position ensures selectivity towards pyruvate whereas an alanine leads to the consumption of both pyruvate and -ketoglutarate. Modifying this residue in P. aeruginosa led to a complete reversal of selectivity. Thus, opine-type metallophore diversity is mainly mediated by the absence/presence of a cntK gene encoding a histidine racemase, and the presence of an aspartate/alanine at position 150 of CntM. These two simple rules predict the production of a fourth metallophore by Paenibacillus mucilaginosus, which was confirmed in vitro and called bacillopaline.

biochemistry↗