Biology subjects

Fenn, S. J.

Publications and source records attributed to Fenn, S. J..

3 recordsLinked to original sources

bioRxiv2026

Copper as a central element critical to interkingdom interactions within a polymicrobial wound environment.

Staphylococcus aureus is a global health concern, estimated to cause over one million deaths each year. To colonise and survive in humans, S. aureus must overcome the host-immune system and compete with other native and invading microorganisms. As a frequent coloniser of wounds, it forms inter-kingdom polymicrobial biofilms, which are associated with impaired wound healing and poorer clinical outcomes. However, the microbial processes that contribute to the competitiveness of S. aureus within infection-related inter-kingdom communities are poorly understood. To address this, we established a polymicrobial in vitro wound-like model (WLM) consisting of two common bacterial pathogens Staphylococcus aureus and Pseudomonas aeruginosa, as well as a the fungal pathobiont Candida albicans. Using a collection of clinical S. aureus strains we then applied a genome-wide association study (GWAS) approach to identify bacterial factors that contribute to S. aureus fitness within this environment. Amongst the six S. aureus loci identified was copA, which encodes a copper exporter that prevents the accumulation of copper in the bacterial cytoplasm. Characterising the molecular processes involved, we identified a 4-way interaction, where C. albicans releases copper from the ceruloplasmin found in the human hosts plasma, which in turn causes a build-up of copper within the S. aureus cytoplasm, rendering the bacteria more susceptible to killing by P. aeruginosa. Human infection data validates the clinical relevance of this, where there is an association between mutations in copA and an origin of infection that is wound-based, highlighting the importance of understanding the entire infection ecosystem if improvements therapeutic approaches are to be developed.

microbiology↗

bioRxiv2026

Metabolic reprogramming promotes Staphylococcus aureus serum resistance during bacteraemia.

Staphylococcus aureus is a leading cause of bloodstream infections causing an estimated 300,000 deaths worldwide. Using a functional genomics approach, our group previously identified that adaptation of S. aureus to human serum is polygenic, with a clinically occurring non-synonymous mutation (V76I) in dihydrolipoamide dehydrogenase (lpdA1/pdhD) improving bacterial survival. In this work we establish that improved serum survival of strains expressing PdhD V76I is underpinned by enhanced resistance to host-derived antimicrobials including antimicrobial peptides and host-defence fatty acids which are prevalent in the bloodstream. Here we demonstrate that the PdhD V76I variant has enhanced diaphorase activity, with both clinical and laboratory strains expressing this variant recycling NADH to NAD+ without using respiration, leading to a reduction in membrane potential. This conferred persister / small colony variant (SCV) like phenotypes on strains expressing PdhD V76I including increased resistance to gentamicin, hydrogen peroxide, LL37, HNP-1 and arachidonic acid. However, strains which utilise PdhD V76I do not display growth defects typical of persisters and SCVs, with reduced NADH accumulation in serum leading to enhanced glycolysis/TCA cycle activity, enhancing bacterial replication in human serum. Whilst establishment of SCV and persister populations is a key survival strategy in the bloodstream, this work demonstrates how intermediate phenotypes can also be effective at promoting survival in this hostile environment. This highlights the heterogenous nature of S. aureus adaptation to the host-environment, with an improved fundamental understanding of these processes required to allow for the development of novel therapeutics which target this process of host-adaptation. IMPORTANCEThe establishment of a bloodstream infection requires the bacteria to be able to withstand the antibacterial factors found there. As one of the major global causes of these types of infections, S. aureus, utilises many diverse strategies to survive and replicate in the bloodstream, which can include modifications to either the cell envelope, or to core metabolic processes such that the hosts immune features are withstood. While extreme adaptations to metabolism can lead to the major growth defects associated with persisters and small colony variants, here we describe a clinically relevant adaption where metabolism was altered such that the bacteria could survive and replicate in serum, but where the growth characteristics of the bacteria were not affected. Mutation of the gene encoding the dihydrolipoamide dehydrogenase enzyme (lpdA1/pdhD) enhanced it diaphorase activity such that it could recycle NADH to NAD+ without using respiration, which led a reduction in membrane potential that conferred resistance to gentamicin, hydrogen peroxide, LL37, HNP-1 and arachidonic acid and human serum, but did not affect growth. This work uncovers a novel mean of adaptation to the bloodstream by S. aureus and highlights how it plasticity underlies its success as a major human pathogen.

microbiology↗

bioRxiv2020

NirA is an alternative nitrite reductase from Pseudomonas aeruginosa with potential as an anti-virulence target

The opportunistic pathogen Pseudomonas aeruginosa produces an arsenal of virulence factors causing a wide range of diseases in multiple hosts and is difficult to eradicate due to its intrinsic resistance to antibiotics. With the antibacterial pipeline drying up, anti-virulence therapy has become an attractive alternative strategy to the traditional use of antibiotics to treat P. aeruginosa infections. To identify P. aeruginosa genes required for virulence in multiple hosts, a random library of Tn5 mutants in PAO1-L was previously screened in vitro for those showing pleiotropic effects in the production of virulence phenotypes. Using this strategy, we have identified a Tn5 mutant with an insertion in PA4130 showing reduced levels in a number of virulence traits in vitro. Construction of an isogenic mutant in this gene presented similar results as those from the Tn5 mutant. Furthermore, the PA4130 isogenic mutant showed substantial attenuation in disease models of Drosophila melanogaster, Caenorhabditis elegans as well as decreased toxicity in human cell lines. This mutant also presented an 80% increased survival in murine acute and agar-bead lung infection models. PA4130 codes for a protein with homology to nitrite and sulphite reductases. Overexpression of PA4130 in the presence of the siroheme synthase CysG enabled its purification as a soluble protein. Methyl viologen oxidation assays with purified PA4130 showed that this protein is a nitrite reductase operating in a siroheme and 4Fe-4S dependant manner. The preference for nitrite and the production of ammonium revealed that PA4130 is an ammonia:ferredoxin nitrite reductase and hence was named as NirA.

microbiology↗