Biology subjects

Handley, K. M.

Publications and source records attributed to Handley, K. M..

9 recordsLinked to original sources

bioRxiv2025

Adaptations of DNA viruses are influenced by host and environment with proliferations constrained by environmental niche

Viruses are ubiquitous albeit individually constrained by host-range. Less well understood are environmental limitations on virus proliferation. To investigate estuarine viral diversity, niche constraints, and genomic traits of environmental adaptation, we analysed metagenomic and metatranscriptomic data from across an estuarine salinity gradient, including water and sediment habitats. We then expanded our analysis to globally distributed viral genomes. Viral distributions varied by estuary habitat, reflecting prokaryote community patterns, and highlighting that virus-host interactions are strongly influenced by environment. Viral lineages, up until approximately the rank of genus, were largely partitioned by ecological niche based on factors such as salinity and the aquatic-terrestrial divide. Across habitat boundaries, we identified variations in genomic GC content, and genomic signatures of salinity adaptation, particularly in virus major tail and capsid proteins. These included elevated ratios of acidic to basic amino acids and decreased protein isoelectric points at higher salinities which did not solely reflect biases inherited due to reliance on host machinery. Salinity is a well-described physiological stressor for prokaryotes. Results suggest that viruses employ some of the same osmoadaptive strategies independent of adaptation based on host machinery. Our findings indicate that, in addition to host range limitations, successful proliferation of viruses into distinct biomes (e.g. freshwater, saline, terrestrial) is constrained by adaptation to specific ecological niches.

microbiology↗

bioRxiv2025

An experimental approach to understanding plastic leachate impacts on marine microorganisms

Plastics in the worlds oceans are exposed to diverse environmental stressors that fragment them, accelerating the leaching of associated additives. The impact of potentially toxic plastic degradation products and additives on marine microorganisms remains poorly understood. We assessed the impact of plastic leachate on marine microbial communities in vitro by exposure to one of four plastic leachates (from linear low-density polyethylene [LLPDE], polyamide-6 [or polycaprolactam; PA6], polyethylene terephthalate [PET] and polylactic acid [PLA]), prepared by immersing plastics in artificial seawater salts broth for three months at 80 {degrees}C. Microbial communities were then exposed to different leachates, noting that lower concentrations of plastic additives leached from the more inert plastic types (LLDPE and PET), as determined by GC-MS. PLA-leachate exposed communities differed significantly in composition from other plastic-leachate-exposed communities (PERMANOVA, P=0.001) as assessed by 16S rRNA gene and ITS region amplicon sequencing. Communities exposed to PLA-leachate contained a higher proportion of Proteobacteria, specifically Halomonas spp., previously reported to degrade LDPE and common plasticisers. Greater relative abundances of Psathyrellaceae fungi also distinguished these communities from those exposed to other plastic leachates. However, despite significant differences in the structure of communities exposed to PLA-leachate, we found no difference in the relative abundances of gene transcripts associated with plastic degradation. While biodegradable plastics such as PLA may persist for shorter times in the environment than more inert plastics, our study indicates greater consequences for marine microbial communities.

microbiology↗

bioRxiv2025

Molecular mechanisms of plastic biodegradation by the fungus Clonostachys rosea

Microbial degradation provides an avenue for the remediation of select plastic polymers contributing to the urgent environmental problem of global plastic pollution. We demonstrate the degradation of polycaprolactone (PCL) by Clonostachys rosea and elucidate its underlying molecular mechanisms. We constructed the genome of this fungal strain and monitored changes in gene expression when exposed to PCL. Twelve genes linked to PCL degradation were found in the genome of C. rosea, and some of them were upregulated in the presence of the plastic, including genes coding for two cutinases. We heterologously expressed the enzymes coded by both genes and confirmed their activity against PCL polymers. We also demonstrate that one of the enzymes was active against polyethylene terephthalate (PET) polymers. Glucose inhibited the expression of both genes, completely halting the plastic biodegradation process, possibly serving as a preferred and readily metabolisable carbon source compared with PCL. We confirm the presence of key metabolic pathways linked to PCL degradation in C. rosea, including fatty acid degradation, providing further evidence of the mechanisms central to plastic biodegradation.

microbiology↗

bioRxiv2023

Bacteroidia and Clostridia perform a progressive cascade of polysaccharide degradation along the hindgut of the herbivorous fish Kyphosus sydneyanus

The gut microbiota of the marine herbivorous fish Kyphosus sydneyanus are thought to play an important role in host nutrition by supplying short-chain fatty acids (SCFA) through fermentation of dietary macroalgae. Here, we assembled 645 metagenome-assembled genomes (MAGs) from wild fish to determine the capacity of different bacterial taxa to degrade seaweed carbohydrates along the gut. Most bacteria (99%) were unclassified at the species level, highlighting taxonomic novelty dominated by Bacteroidia and Clostridia within the gut community. The presence of genes encoding endo-acting CAZymes in both phyla suggest they have a role in initiating glycan depolymerization. Bacteroidia also contributed the most to CAZyme-related gene expression in the distal hindgut, and encoded the highest densities of CAZymes within the community. In particular, the enrichment of CAZyme gene clusters (CGCs) within the Bacteroidia genus Alistipes (n = 73 versus just 59 distributed across all other taxa) points to an enhanced capacity for macroalgal polysaccharide utilization (e.g., alginate, laminarin and sulfated polysaccharides). Pairwise correlations of MAG relative abundances and encoded CAZyme compositions provide evidence of potential inter-species collaborations, whereby co-abundant MAGs exhibited complementary degradative capacities for specific substrates. Results indicated flexibility across these co-abundant groups in their capacity to source carbon (e.g., glucose or galactose-rich glycans), which possibly facilitates coexistence via niche partitioning. Our results indicate the potential for collaborative microbial carbohydrate metabolism in the gut of K. sydneyanus by Bacteroidia and Clostridia, and suggest that members of the genus Alistipes are a metabolically and taxonomically diverse group of specialized macroalgae biomass degraders.

microbiology↗

bioRxiv2022

Genetic exchange shapes ultra-small Patescibacteria metabolic capacities in the terrestrial subsurface

Bacterial genomes are highly dynamic entities, mostly due to the extent of horizontal gene transfer (HGT) occurring in these organisms. HGT is thought to be the main driver of genetic variation and adaptation to local environment in bacteria. However, little is known about the modalities of HGT within natural microbial communities, especially the implications of genetic exchange for streamlined microorganisms such as Patescibacteria (Candidate Phyla Radiation). We searched for evidence of genetic exchange in 125 Patescibacteria genomes recovered from aquifer environments and detected the presence of hundreds of genomic islands, individually transferred genes and prophage combined, with up to 29% of genome length attributed to HGT. Results show that most individual gene transfer events occurred between Patescibacteria, but donors were also phylogenetically diverse groundwater microorganisms. Using gene donor-recipient information, we identified one potential host (Omnitrophota) of the ultra-small bacteria, and confirmed this by matching relative abundance patterns across 16 groundwater samples. A wide variety of metabolic functions were introduced in Patescibacteria genomes by HGT including transcription, translation and DNA replication, recombination and repair. This study illustrates the evolutionarily dynamic nature of Patescibacteria genomes despite the constraints of streamlining, and that HGT in these organisms is also mediated via viral infection.

evolutionary biology↗

bioRxiv2021

Metabolic diversity and aero-tolerance in anammox bacteria from geochemically distinct aquifers

BackgroundAnaerobic ammonium oxidation (anammox) is important for converting bioavailable nitrogen into dinitrogen gas, particularly in carbon poor environments. Yet, the diversity and prevalence of anammox bacteria in the terrestrial subsurface - a typically oligotrophic environment - is little understood across different geochemical conditions. To determine the distribution and activity of anammox bacteria across a range of aquifer lithologies and physicochemistries, we analysed 16S rRNA genes, metagenomes and metatranscriptomes, and quantified hydrazine synthase genes and transcripts sampled from 59 groundwater wells distributed over 1 240 km2. ResultsData indicate that anammox-associated bacteria (class Brocadiae) and the anammox process are prevalent in aquifers (identified in aquifers with sandy-gravel, sand-silt and volcanic lithologies). While Brocadiae diversity decreased with increasing DO, Brocadiae 16S rRNA genes and hydrazine synthase genes and transcripts (hydrazine synthase, hzsB) were detected across a wide range of bulk groundwater dissolved oxygen (DO) concentrations (0 - 10 mg/L). Anammox genes and transcripts (hzsB) correlated significantly with those involved in bacterial and archaeal ammonia oxidation (ammonia monooxygenase, amoA), which could represent a major source of nitrite for anammox. Differences in anammox community composition were strongly associated with DO and bore depth (and to a lesser extent pH and phosphate), revealing niche differentiation among anammox bacteria in groundwater that was largely driven by water oxygen contents, and not ammonium/nitrite. Eight Brocadiae genomes (63-95% estimated completeness) reconstructed from a subset of groundwater sites belong to 2 uncharacterized families and 6 novel species (based on average nucleotide identity). Distinct groups of these genomes dominated the anammox-associated community at dysoxic and oxic sites, further reflecting the influence of DO on Brocadiae composition. Six of the genomes (dominating dysoxic or oxic sites) have genes characteristic of anammox (hydrazine synthase and/or dehydrogenase). These genes, in addition to aerotolerance genes, belonging to four Brocadiae genomes, were transcriptionally active, although transcript numbers clearly highest in dyoxic groundwater. ConclusionsOur findings indicate anammox bacteria contribute to loss of fixed N across diverse anoxic-to-oxic aquifer conditions, and that this is likely supported by nitrite from aerobic ammonia oxidation. Results provide an insight into the distribution and activity of anammox bacteria across distinct aquifer physicochemisties.

microbiology↗

bioRxiv2021

Effect of dietary zinc supplementation on the gastrointestinal microbiota and host gene expression in the Shank3B-/- mouse model of autism spectrum disorder

Shank genes are implicated in ~1% of people with autism and mice with Shank3 knock out mutations exhibit autism-like behaviours. Zinc deficiency and gastrointestinal problems can be common among people with autism, and zinc is a key element required for SHANK protein function and gut development. In Shank3B-/- mice, a supplementary zinc diet reverses autism behaviours. We hypothesise that dietary zinc may alter the gut microbiome, potentially affecting the gut-microbiome-brain axis, which may contribute to changes in autism-like behaviours. To test this, four types of gastrointestinal samples (ileum, caecum, colon, faecal) were collected from wild-type and knock-out Shank3B-/- mice on either control or supplemented-zinc diets. Cage, genotype and zinc diet each contributed significantly to bacterial community variation (accounting for 12.8%, 3.9% and 2.3% of the variation, respectively). Fungal diversity differed significantly between wild-type and knock-out Shank3B-/- mice on the control zinc diet, and the fungal biota differed among gut locations. RNA-seq analysis of host (mouse) transcripts revealed differential expression of genes involved in host metabolism that may be regulated by the gut microbiota and genes involved in anti-microbial interactions. By utilising the Shank3B-/- knock-out mouse model we were able to examine the influence of - and interactions between - dietary zinc and ASD-linked host genotype. These data broaden understanding of the gut microbiome in autism and pave the way towards potential microbial therapeutics for gastrointestinal problems in people with autism. ImportancePreviously, supplemental dietary zinc in the Shank3B-/- mouse model of autism spectrum disorder resulted in observations of ASD behaviours reversal; in this study we also used the Shank3B-/- mouse model to examine the influence of - and interaction between - dietary zinc and ASD-linked host genotype. Sample location along the gastrointestinal tract, genotype and zinc diet explained some of the variation in the microbiota data, with notable bacterial differences between treatment groups. Differential expression of host genes between treatment groups, including antimicrobial interaction genes and gut microbiota-regulated host metabolism genes, suggests that the interplay between gut microbes, the gastrointestinal tract and the brain may play a major role towards the observed amelioration of ASD behaviours seen previously with supplemented dietary zinc. These results widen the scope towards manipulating both dietary zinc and the microbiota itself to ameliorate ASD-related behaviours and associated gastrointestinal issues.

microbiology↗

bioRxiv2021

Rethinking symbiotic metabolism: trophic strategies in the microbiomes of different sponge species

In this study we describe the major lithoheterotrophic and autotrophic processes in 21 microbial sponge-associated phyla using novel and existing genomic and transcriptomic datasets. We show that a single gene family, molybdenum-binding subunit of dehydrogenase (coxL), likely evolved to benefit both lithoheterotrophic and organoheterotrophic symbionts, through adaptation to different inorganic and organic substrates. We show the main microbial carbon fixation pathways in sponges are restricted to specialized symbiotic lineages within five phyla. We also propose that sponge symbionts, in particular Acidobacteria, are capable of assimilating carbon through anaplerotic processes. However, the presence of symbionts genomically capable of autotrophy does not inform on their actual contribution to light and dark carbon fixation. Using radioisotope assays we identified variability in the relative contributions of chemosynthesis to total carbon fixation in different sponge species. Furthermore, the symbiosis of sponges with two closely related Cyanobacteria results in outcomes that are not predictable by analysis of -omics data alone: Candidatus Synechococcus spongiarum contributes to the holobiont carbon budget by transfer of photosynthates, while Candidatus Synechococcus feldmannii does not. Our results highlight the importance of combining sequencing data with physiology to gain a broader understanding of carbon metabolism within holobionts characterized by highly diverse microbiomes.

microbiology↗

bioRxiv2016

Metabolic and spatio-taxonomic response of uncultivated seafloor bacteria following the Deepwater Horizon oil spill

The release of 700 million liters of oil into the Gulf of Mexico over a few months in 2010 produced dramatic changes in the microbial ecology of the water and sediment. Previous 4 studies have examined the phylogeny and function of these changes, but until now a 5 fundamental examination of the extant hydrocarbon metabolisms that supported these 6 changes had not been performed. Here, we reconstructed the genomes of 57 widespread 7 uncultivated bacteria from post spill sediments, and recovered their gene expression 8 pattern across the seafloor. These genomes comprised a common collection of bacteria 9 that were highly enriched in heavily affected sediments around the wellhead. While rare in distal sediments, some members were still detectable at sites up to 60 km away. Many of these genomes exhibited phylogenetic clustering indicative of common trait selection by the environment, and within half we identified 264 genes associated with hydrocarbon degradation. Observed alkane degradation ability was near ubiquitous among candidate hydrocarbon degraders, while just 3 harbored elaborate gene inventories for the degradation of alkanes and (poly)aromatic hydrocarbons. Differential gene expression profiles revealed a spill-promoted microbial sulfur cycle alongside gene up-regulation associated with polyaromatic hydrocarbon degradation. Gene expression associated with alkane degradation was widespread, although active alkane degrader identities changed along the pollution gradient. The resulting analysis suggests a broad metabolic capacity to respond to oil exists across a large array of usually rare bacteria.

microbiology↗