Biology subjects

Le Mauff, F.

Publications and source records attributed to Le Mauff, F..

6 recordsLinked to original sources

bioRxiv2026

Exploring the antibiotic-producing capabilities of Canadian High Arctic bacteria

Microbial communities in harsh environments such as the Canadian high Arctic, remain a relatively unexplored source of antimicrobial natural products. In this study, we developed a pipeline for screening and evaluating bacterial isolates cultured from 23 Canadian high Arctic soil, sediment, and active-layer permafrost samples to discover antibacterial compounds. The pipeline incorporated an undergraduate studentsourcing program and produced created a collection of over 350 bacterial isolates with preliminary antibacterial activity. Following dereplication, whole genome sequencing and secondary screening by co-culture assays, five isolates were prioritized to test crude extracts for antibacterial activity. Among bioactive crude extracts from these isolates, the Pseudomonas isolate with the most potent activity against S. aureus was analyzed. Using liquid chromatography bioactivity guided fractionation, we identified a potential bioactive compound known as koreenceine A, a compound previously only isolated from a Pseudomonas from temperate soil and involved in gene expression of other their microbial community. Here we expanded the known antibiotic activity of koreenceine A and confirmed that a {triangleup}kecBCD genetic knockout of the putative biosynthetic gene cluster significantly abrogated the antibacterial activity.

microbiology↗

bioRxiv2026

A strain-specific metabolic role for the UDP-glucose 4-epimerase Uge3 in Aspergillus fumigatus virulence

Expression of a fungal-specific sub-telomeric gene, hrmA, in Aspergillus fumigatus is important for a colony biofilm morphology termed H-MORPH, increased hypoxic fitness, and virulence in a murine model of invasive pulmonary aspergillosis (IPA). How expression of hrmA contributes to virulence and worse disease progression is ill-defined. Increased hrmA expression results in reduced attachment of the extracellular matrix (ECM) to the fungal cell wall resulting in decreased strain adherence. Fungal strains that are less adherent in vitro are typically less virulent as the ECM heteropolysaccharide galactosaminogalactan (GAG) aids in adhesion to host cells and confers protection from host responses. Here we report that the UDP-glucose 4-epimerase encoding gene required for GAG biosynthesis, uge3, is necessary for full virulence of the H-MORPH strain, hrmAREV (AF293::hrmAD304G). In contrast, loss of uge3 in the reference strain AF293 did not significantly impact virulence in the tested IPA murine model. Phenotypic, transcriptomic, and metabolic analyses of uge3 loss in the respective strain backgrounds revealed a key role for Uge3 in central carbon metabolism in a strain specific context that promotes disease progression. These results complement the known role of Uge3 in GAG biosynthesis and highlight strain specific metabolic differences in pathogenic A. fumigatus strains. IMPORTANCEAspergillus fumigatus forms adherent biofilms that contribute to its ability to persist and cause disease. However, significant strain diversity exists with regard to the morphology of A. fumigatus biofilms. A distinct colony morphotype associated with increased disease progression and low oxygen fitness, termed H-MORPH, was recently described. An additional defining feature of the H-MORPH biofilm morphotype is reduced in vitro adherence to surfaces. While reduced fungal strain adherence is most commonly associated with reductions in virulence, H-MORPH strains exhibit increased virulence relative to the well-studied N-MORPH reference strain AF293. Here we discover that the UDP-glucose 4-epimerase, Uge3, plays an important role in H-MORPH central carbon metabolism complementary to its role in production of the extracellular matrix polysaccharide galactosaminogalactan (GAG). In H-MORPH strains, this metabolic role for Uge3 becomes central to virulence. These data highlight A. fumigatus strain specific mechanisms of fungal carbon metabolism related to biofilm matrix production and fungal virulence.

microbiology↗

bioRxiv2024

Structural and functional analysis of Pseudomonas aeruginosa PelA provides insight into the modification of the Pel exopolysaccharide

A major biofilm matrix determinant of Pseudomonas aeruginosa is the partially deacetylated -1,4 linked N-acetylgalactosamine polymer, Pel. After synthesis and transport of the GalNAc polysaccharide across the inner membrane, PelA partially deacetylates and hydrolyzes Pel before its export out of the cell via PelB. While the Pel modification and export proteins are known to interact in the periplasm, it is unclear how the interaction of PelA and PelB coordinates these processes. To determine how PelA modifies the polymer, we determined its structure to 2.1 [A] and found a unique arrangement of four distinct domains. We have shown previously that the hydrolase domain exhibits endo--1,4-N-acetylgalactosaminidase activity. Characterization of the deacetylase domain revealed that PelA is the founding member of a new carbohydrate esterase family, CE#. Further, we found that the PelAB interaction enhances the deacetylation of N-acetylgalactosamine oligosaccharides. Using the PelA structure in conjunction with AlphaFold2 modelling of the PelAB complex, we propose a model wherein PelB guides Pel to the deacetylase domain of PelA and subsequently to the porin domain of PelB for export. Perturbation or loss of the PelAB interaction would result in less efficient deacetylation and potentially result in increased Pel hydrolysis. In PelA homologues across many phyla, the predicted structure and active sites are conserved, suggesting that there is a common modification mechanism in Gram-negative bacterial species that contain a functional pel operon.

microbiology↗

bioRxiv2024

Autoaggregation in Streptococcus intermedius is driven by the Pel polysaccharide

The Streptococcus Milleri Group (SMG) comprising of Streptococcus intermedius, anginosus and constellatus are commensal bacteria commonly found in healthy individuals. These bacteria are increasingly being recognized as opportunistic pathogens that can cause purulent infections at sterile body sites and have also been identified in the sputum of individuals with cystic fibrosis. Although the mechanisms of conversion to opportunistic pathogens are not well understood, auto-aggregation is a key driver of biofilm adhesion and cohesion in many Streptococci and Staphylococci. Here, we identify a gene cluster in the S. intermedius genome with significant homology to the pel operons in Bacillus cereus and Pseudomonas aeruginosa, which are required for Pel exopolysaccharide production and biofilm formation in these species. Characterization of a panel of clinical S. intermedius strains identified a range of aggregating phenotypes. Analysis of the pel operon in the hyper-aggregating C1365 strain revealed that each of the canonical pelDEADAFG genes, but not the four additional genes are required for aggregation. Further, we demonstrate that C1365 produces a GalNAc-rich exopolysaccharide and that aggregates can be disrupted by the 1,4 N-acetylgalactosaminidases, PelA and Sph3, but not other glycoside hydrolases, proteinase K or DNase I. Using an abscess model of mouse infection, we show that Pel driven aggregation leads to longer lasting infections, and that lack of Pel allows for the bacteria to be cleared more effectively. The polymer also affects how the bacteria interacts with the host immune system. Collectively, our data suggest that the pel operon has relevancy to S. intermedius pathogenicity.

microbiology↗

bioRxiv2023

CD56-mediated activation of human natural killer cells is triggered by Aspergillus fumigatus galactosaminogalactan

Invasive aspergillosis causes significant morbidity and mortality in immunocompromised patients. Natural killer (NK) cells are pivotal for antifungal defense. Thus far, CD56 is the only known pathogen recognition receptor on NK cells triggering potent antifungal activity against Aspergillus fumigatus. However, the underlying cellular mechanisms and the fungal ligand of CD56 have remained unknown. Using purified cell wall components, biochemical treatments, and A. fumigatus mutants with altered cell wall composition, we herein found that CD56 interacts with the A. fumigatus cell wall carbohydrate galactosaminogalactan (GAG). This interaction induced NK cell activation, degranulation, and secretion of immune-enhancing chemokines and cytotoxic effectors. Supernatants from GAG-stimulated NK cells elicited antifungal activity and enhanced antifungal effector responses of polymorphonuclear cells. In conclusion, we identified A. fumigatus GAG as a ligand of CD56 on human primary NK cells, stimulating potent antifungal effector responses and activating other immune cells.

microbiology↗

bioRxiv2021

An Alanine Aminotransferase is Required for Polysaccharide Regulation and Resistance of Aspergillus fumigatus Biofilms to Echinocandin Treatment

Alanine metabolism has been suggested as an adaptation strategy to oxygen limitation in organisms ranging from plants to mammals. Within the pulmonary infection microenvironment A. fumigatus forms biofilms with steep oxygen gradients defined by regions of oxygen limitation. A significant increase in alanine levels was observed in A. fumigatus cultured under oxygen limiting conditions. An alanine aminotransferase, AlaA, was observed to function in alanine catabolism and is required for several aspects of A. fumigatus biofilm physiology. Loss of alaA, or its catalytic activity, results in decreased adherence of biofilms through a defect in the maturation of the extracellular matrix polysaccharide galactosaminogalactan (GAG). Additionally, exposure of cell wall polysaccharides is also impacted by loss of alaA and loss of AlaA catalytic activity confers increased biofilm susceptibility to echinocandin treatment which is correlated with enhanced fungicidal activity. The increase in echinocandin susceptibility is specific to biofilms and chemical inhibition of alaA by the alanine aminotransferase inhibitor {beta}-chloro-L-alanine is sufficient to sensitize A. fumigatus biofilms to echinocandin treatment. Finally, loss of alaA increases susceptibility of A. fumigatus to in vivo echinocandin treatment in a murine model of invasive pulmonary aspergillosis. Our results provide insight into the interplay of metabolism, biofilm formation, and antifungal drug resistance in A. fumigatus and describes a mechanism of increasing susceptibility of A. fumigatus biofilms to the echinocandin class of antifungal drugs. eLife DigestAspergillus fumigatus is a ubiquitous filamentous fungus that causes an array of diseases depending on the immune status of an individual, collectively termed aspergillosis. Antifungal therapy for invasive pulmonary aspergillosis (IPA) or chronic pulmonary aspergillosis (CPA) is limited and too often ineffective. This is in part due to A. fumigatus biofilm formation within the infection environment and the resulting emergent properties, particularly increased antifungal resistance. Thus, insights into biofilm formation and mechanisms driving increased antifungal drug resistance are critical for improving existing therapeutic strategies and development of novel antifungals. In this work, we describe an unexpected observation where alanine metabolism, via the alanine aminotransferase AlaA, is required for several aspects of A. fumigatus biofilm physiology including resistance of A. fumigatus biofilms to the echinocandin class of antifungal drugs. Importantly, we observed that chemical inhibition of alanine aminotransferases is sufficient to increase echinocandin susceptibility and that loss of alaA increases susceptibility to echinocandin treatment in a murine model of IPA.

microbiology↗