Biology subjects

Hug, L. A.

Publications and source records attributed to Hug, L. A..

At least 19 recordsLinked to original sources

bioRxiv2026

The origin and evolution of archaeal Borg extrachromosomal elements

Borgs are giant linear extrachromosomal elements (ECEs) of methane-oxidizing Methanoperedens archaea whose evolutionary origin and ecosystem distribution remain unknown. Here we detected 240 Borgs in diverse saline, soil, and freshwater ecosystems. 27 encode methyl-coenzyme M reductases central to methane metabolism, eight have full rRNA operons related to those of Methanoperedens, and some contain up to four ribosomal proteins. We also identified 323 mini-Borgs whose proteome content and gene phylogenies classify as a distinct ECE type. Based on 105 complete and near-complete genomes, Borgs and mini-Borgs share core genes in conserved order, indicating common ancestry. Phylogenetic and diversity analyses suggest that Borgs evolved via gene acquisition into a backbone inherited from mini-Borgs. This evolutionary trajectory mirrors those proposed for giant viruses of both eukaryotes and bacteria.

microbiology↗

bioRxiv2026

Host cohort has a larger impact on the gut microbiomes of mealworms and superworms than does the ingestion of polyethylene or polystyrene

Beetles (order Coleoptera) are a diverse insect group whose associated microbial communities remain understudied despite their ecological, commercial, and biotechnological importance. Larvae of the darkling beetle species Tenebrio molitor (mealworms) and Zophobas atratus (superworms) have gained attention for their reported ability to ingest and possibly degrade plastics such as polyethylene and polystyrene. This degradation is believed to be mediated by enzymes from their gut microbiota, yet the underlying microbial mechanisms remain unclear. Using deep shotgun metagenomics, we generated comprehensive gut metagenomes for mealworms and superworms, recovering 53 and 100 high-quality metagenome-assembled genomes (MAGs), respectively. We found that the gut microbiomes of both insect species are dominated by bacteria from the phyla Bacillota and Pseudomonadota, with superworms trending towards greater bacterial diversity than mealworms. Comparing gut bacterial communities of insects fed polyethylene or polystyrene versus controls revealed no clear plastic ingestion effects beyond those attributable to starvation. On the other hand, insect cohort contributed substantially to variation in bacterial community composition, explaining 23% and 33% of the total variation in mealworms and superworms, respectively. Finally, we computationally identified numerous secreted proteins with sequence similarity to enzymes previously implicated in polyethylene and polystyrene degradation, and we provide support for dye decolorizing peroxidase (DyP)-type peroxidases as being the enzyme class mostly likely to initiate plastic oxidation in the digestive tracts of mealworms and superworms. Overall, this study provides high-quality metagenomes and MAGs for mealworms and superworms, revealing substantial under-explored microbial biodiversity, and highlighting DyP-type peroxidases as promising targets for future plastic biodegradation studies.

microbiology↗

bioRxiv2026

Diverse microbial metal resistance and novel metal cycling organisms in copper/nickel mine tailings

Mine tailings contribute to environmental heavy metal contamination through the formation of acid mine drainage (AMD). Microbially-mediated processes such as iron and sulfur redox cycling influence metal mobility. Here, we applied an integrated metagenomic and metaproteomic approach to profile microbial communities across vertical geochemical gradients in legacy copper/nickel tailings in Sudbury, Ontario, Canada. From 43 samples, we recovered 454 non-redundant metagenome-assembled genomes (MAGs), revealing diverse populations within the Actinobacteriota, Desulfobacterota, and uncultured lineages such as Candidatus Eremiobacterota and SZUA-79. Functional profiling identified 301 putative iron- and sulfur-cycling MAGs, including those within the Ca. Eremiobacterota and SZUA-79 phyla. Metal resistance genes were widespread and diverse, with abundances that did not correlate with measured metal concentrations. Proteomic data confirmed in situ expression of selected metal resistance genes and iron/sulfur metabolism genes, despite limited protein recovery from this challenging matrix. Our findings highlight both the depth of microbial diversity in metal resistance and metal biogeochemical cycling in mining waste, as well as the technical challenges that currently limit genomic and proteomic sequencing coverage in low-biomass, metal-rich matrices. This work also presents new protocols for multi-omics data capture and analysis from metal contaminated environments, including new protein extraction and bioinformatic gene annotation tools. HighlightsO_LIMetagenomics recovered 454 non-redundant MAGs from copper/nickel mine tailings, revealing high taxonomic novelty including uncultured Ca. Eremiobacterota and SZUA-79 lineages. C_LIO_LIA custom HMM-based pipeline targeting metal resistance genes uncovered a widespread and diverse set of metal resistance genes across MAGs in tailings, which did not correlate with metal concentrations. C_LIO_LIMetaproteomics validated in situ expression of both iron/sulfur cycling genes and metal resistance proteins, although low biomass and contamination limited proteomic sequencing coverage. C_LI

microbiology↗

bioRxiv2026

Tracking interlinked microbial and geochemical succession over decades in landfilled municipal solid waste

Landfills are heterogeneous built environments embedded in natural freshwater systems. They pose increasing risks of groundwater contamination from metal-bearing leachates over time. The interlinked succession of waste decomposition processes, microbial community membership and metal cycling across a landfills lifespan have not been explored, reducing our ability to predict the long-term environmental impacts of landfills. Working with 1,647 metagenome-assembled genomes from a single landfill, from samples spanning over 39 years of waste decomposition, we identified changes in landfill biogeochemistry and connected these changes to shifts in microbial community composition and predicted functions over time. Comparing between Older (aged 31 - 39 years) and Newer (aged 3 - 20 years) waste cells identified significant shifts in the availability of labile carbon, redox-associated processes, and concentrations of mobile metals - all higher in Newer cells. Newer cells were dominated by chemoorganoheterotrophs, while Older cells contained higher proportions of chemolithoautotrophs and organisms with higher metabolic versatility. Metal resistance and metal cycling genes were significantly more abundant in Older cells. Using geochemistry data from time of filling to present and microbial membership across six landfill cells of different ages, we developed a conceptual model of landfill characteristics across time. This model connects redox conditions and metal fate, highlighting leachate recirculation as a key process impacting many geochemical parameters and defining site chemistry. Our work highlights the substantial changes occurring over the stabilization phase and provides a conceptual framework for understanding this critical, final stage in a landfills life cycle. ImportanceAging landfills pose significant risks to environmental stability and are currently poorly modeled beyond [~]20 years. Our examination of a single landfill across 39 years of waste degradation was a unique opportunity to examine the impact of time within a connected system. Our work connects geochemical data, microbial membership and predicted function, as well as physical processes (e.g., leachate recirculation). Our conceptual model interlinks these facets across the lifespan of a landfill, providing an empirical data-based model of landfill aging. Previous models were extrapolated from younger waste and did not include the microbial dimension - a critical facet of the landfill ecosystem. Our model clarifies processes taking place in older wastes (30+ years), including oxygen infiltration, that have important implications for methane emission and metal mobility and fate over the longer-term.

microbiology↗

bioRxiv2025

Methanotroph dynamics at landfill cover soil methane emission hotspots

Landfills contribute significant emissions to the global methane cycle, where emission hotspots can account for the majority of methane released. Methanotrophs in landfill cover soils can mitigate these methane emissions, but are constrained by geochemical conditions in the soils and the climate at the landfills location. We sampled cover soils from four Ontario landfills with differing characteristics, including measurements of methane flux, soil methane concentration, and a suite of geochemical variables. Sampling sites were distinguished based on the levels of methane flux. Microbial community diversity and methanotroph dynamics were examined using 16S rRNA gene amplicon sequencing. Sites with high methane emissions showed strong enrichment of methanotrophs, dominated by the genus Methylomicrobium. The distribution of methanotrophs in samples across landfills and sites differed significantly when considering community evenness. Of the environmental factors examined, microbial community diversity correlated most strongly to nitrate and nitrite concentrations. Methanotroph dynamics across different methane exposures and geochemical conditions within landfill cover soils inform the use of designer cover soils and/or methanotroph amendments in efforts toward mitigating methane emissions from landfills.

microbiology↗

bioRxiv2025

Planetary-scale metagenomic search reveals new patterns of CRISPR targeting

Interactions between microbes and their mobile genetic elements (MGEs), including viruses and plasmids, are critical drivers of microbiome structures and processes. CRISPR-Cas systems are important regulators of these host-MGE interactions, but a global understanding of CRISPR loci diversity, activity, and roles across Earths biomes is still lacking. Here, we use an optimized computational approach to search short-read data and collect [~]800 million CRISPR spacers across [~]450,000 public metagenomes. From this extensive CRISPR spacer dataset, we identified 1.18 billion hits between 41 million spacers and 2.5 million viruses and plasmids. Focusing on the role of CRISPR as anti-phage defense, we observed an over-representation of prevalent and conserved spacers consistent with a positive selection pressure associated with phage targeting. Identification of sustained CRISPR targeting by microbes not expected to be viable hosts suggested that some phage genomes may frequently enter non-host microbial cells. Taken together, these results outline the extensive diversity of CRISPR loci across microbiomes, and highlight key parameters driving CRISPR targeting patterns likely to influence strain-level diversification and selection processes within microbial populations.

microbiology↗

bioRxiv2024

Aquifer microbial communities are highly variable in response to thermal arsenic mobilization

Thermal recovery technologies for in-situ bitumen extraction can result in the heating of surrounding aquifers, potentially mobilizing arsenic naturally present in the sediments to the groundwater. The relative toxicity of dissolved arsenic is related to its speciation, with As(V) being less toxic than As(III). Microorganisms have various mechanisms of arsenic resistance, including efflux and methylation. Microorganisms may also perform reduction/oxidation of As(V)/As(III) as part of their detoxification and/or metabolic pathways. We characterized the microbial communities along two aquifer transects associated with thermally mobilized arsenic near Northeastern Alberta oil sands deposits. 16S rRNA amplicons and metagenomic sequencing data of biomass from filtered groundwater indicated major changes in the dominant taxa between wells, especially those currently experiencing elevated arsenic concentrations. Annotation of arsenic-related genes indicated that efflux pumps (arsB, acr3), intracellular reduction (arsC) and methylation (arsM) genes were widespread amongst community members but comparatively few organisms encoded genes for arsenic respiratory reductases (arrA) and oxidases (arxA, aioA). While this indicates that microbes have the capacity to exacerbate arsenic toxicity by increasing the relative concentration of As(III), some populations of iron oxidizing and sulfate reducing bacteria (including novel Gallionella and Thermodesulfovibrionia populations) show potential for indirect bioremediation through formation of insoluble iron/sulfide minerals which adsorb or coprecipitate arsenic. An unusually high proportional abundance of a single Paceibacteria population that lacked arsenic resistance genes was identified in one high-arsenic well, and we discuss hypotheses for its ability to persist. Overall, this study describes how aquifer microbial communities respond to thermal and arsenic plumes, and predicts potential contributions of microbes to arsenic biogeochemical cycling under this disturbance.

microbiology↗

bioRxiv2024

A roadmap for fair reuse of public microbiome data

Science benefits from rapid, open data sharing but samples for sequencing data are expensive for data creators to acquire and process. Current guidelines for data reuse were established two decades ago, when databases were several million times smaller, necessitating an update. This article presents a roadmap to establish best practices for sequence data reuse, developed in consultation with a data consortium of 167 microbiome scientists. It introduces a Data Reuse Information tag (DRI) for public sequencing data, which will be associated with at least one Open Researcher and Contributor ID (ORCID) account. The machine-readable DRI tag indicates that the data creators prefer to be contacted prior to data reuse, and simultaneously provides data consumers with a mechanism to get in touch with the data creators. Ideally, the DRI will facilitate and foster collaborations, and serve as a guideline that can be expanded to other data types.

microbiology↗

bioRxiv2024

Discarded diversity: Novel megaphages, auxiliary metabolic genes, and virally encoded CRISPR-Cas systems in landfills

BackgroundViruses are the most abundant microbial entity on the planet, impacting microbial community structure and ecosystem services. Despite outnumbering Bacteria and Archaea by an order of magnitude, viruses have been comparatively underrepresented in reference databases. Metagenomic examinations have illustrated that viruses of Bacteria and Archaea have been specifically understudied in engineered environments. Here we employed metagenomic and computational biology methods to examine the diversity, host interactions, and genetic systems of viruses predicted from 27 samples taken from three municipal landfills across North America. ResultsWe identified numerous viruses that are not represented in reference databases, including the third largest bacteriophage genome identified to date ([~]678 kbp), and note a cosmopolitan diversity of viruses in landfills that are distinct from viromes in other systems. Host-virus interactions were examined via host CRISPR spacer to viral protospacer mapping which captured hyper-targeted viral populations and six viral populations predicted to infect across multiple phyla. Virally-encoded auxiliary metabolic genes (AMGs) were identified with the potential to augment hosts methane, sulfur, and contaminant degradation metabolisms, including AMGs not previously reported in literature. CRISPR arrays and CRISPR-Cas systems were identified from predicted viral genomes, including the two largest bacteriophage genomes to contain these genetic features. Some virally encoded Cas effector proteins appear distinct relative to previously reported Cas systems and are interesting targets for potential genome editing tools. ConclusionsOur observations indicate landfills, as heterogeneous contaminated sites with unique selective pressures, are key locations for diverse viruses and atypical virus-host dynamics.

microbiology↗

bioRxiv2024

Legacy copper/nickel mine tailings potentially harbor novel iron/sulfur cycling microorganisms within highly variable communities

The oxidation of sulfide-bearing mine tailings catalysed by acidophilic iron and sulfur-oxidizing bacteria releases toxic metals and other contaminants into soil and groundwater as acid mine drainage. Understanding the environmental variables that control the community structure and metabolic activity of endogenous microbes living in tailings (especially the abiotic stressors of low pH and high dissolved metal content) is crucial to developing sustainable bioremediation strategies. We determined the microbial community composition along two continuous vertical gradients of Cu/Ni mine tailings at each of two tailings impoundments near Sudbury, Ontario. 16S rRNA amplicon data showed high variability in community diversity and composition between locations, as well as at different depths within each location. A temporal comparison for one tailings location showed low fluctuation in microbial communities across 2 years. Differences in community composition correlated most strongly with pore-water pH, Eh, alkalinity, salinity, and the concentration of several dissolved metals (including iron, but not copper or nickel). The relative abundances of individual genera differed in their degrees of correlation with geochemical factors. Several abundant lineages present at these locations have not previously been associated with mine tailings environments, including novel species predicted to be involved in iron and sulfur cycling.

microbiology↗

bioRxiv2023

Giant genes are rare but implicated in cell wall degradation by predatory bacteria

Across the tree of life, gene lengths vary, but most are no more than a few thousand base pairs in length. The largest protein often reported is the [~]40,000 aa eukaryotic Titin. Even larger proteins may occur in the rapidly expanding set of metagenome-derived sequences, but their existence may be obscured by assembly fragmentation. Here, we leverage genome curation to complete metagenome-derived sequences that encode predicted proteins of up to 85,804 aa. Overall, the findings illuminate a huge knowledge gap related to giant proteins. Although predicted proteins of >30,000 aa occur in bacterial phyla such as Firmicutes and Actinobacteria, they are most common in ca. Omnitrophota, ultra small bacteria that adopt predatory lifestyles. All full length giant genes encode numerous transmembrane regions and most encode divergent secA DEAD helicase domains. In silico structural prediction of protein subregions was required to identify domains in unannotated protein segments, and revealed putative domains implicated in attachment and carbohydrate degradation. Many giant genes in new complete and near-complete Omnitrophota genomes occur in close proximity to genes homologous to type II secretion systems as well as carbohydrate import systems. This, in combination with the domain content, suggests that many bacterial giant proteins enable prey adhesion and cell wall digestion during bacterial predation.

microbiology↗

bioRxiv2023

Microbial methane cycling in a landfill on a decadal time scale

Landfills generate outsized environmental footprints due to microbial degradation of organic matter in municipal solid waste, which produces the potent greenhouse gas methane. With global solid waste production predicted to increase 69% by the year 2050, there is a pressing need to better understand the biogeochemical processes that control microbial methane cycling in landfills. In this study, we had the rare opportunity to characterize the microbial community responsible for methane cycling in landfill waste covering a 39-year timeframe. We coupled long term geochemical analyses to whole-community DNA (i.e., metagenomic) sequencing and identified key features that shape methane cycling communities over the course of a landfills lifecycle. Anaerobic methanogenic microbes are more abundant, diverse, and metabolically versatile in newer waste, fueling rapid methane production early in a landfills lifecycle. Aerobic methanotrophs were repeatedly found in leachate where low levels of oxygen were present and exhibited adaptations that aid survival under steep redox gradients in landfills. The potential for anaerobic methane oxidation, which has historically been overlooked despite anoxic habitats dominating landfills, was prevalent in a 26-year-old landfill cell which was in a state of slow methanogenesis. Finally, we identified the metabolic potential for methane oxidation in lineages that are widespread in aquatic and terrestrial habitats, whose capacity to metabolize methane remains poorly characterized. Ultimately, this work expands the diversity of methane cycling guilds in landfills and outlines how these communities can curb methane emissions from municipal solid waste. SignificanceMicrobes are major contributors to methane emissions from solid waste however the temporal dynamics of methane cycling communities in landfills remain poorly understood. We addressed this gap by using whole-community DNA (i.e., metagenomic) approaches to characterize microbial methane cycling in waste covering a 39-year timeframe. We show that methane-producing microbes are more abundant, diverse, and metabolically versatile in new waste compared to old waste. We highlight that methane oxidation in the absence of oxygen is overlooked in landfill biogeochemical models and that novel lineages can potentially contribute to methane sinks across a broad range of habitats. These findings can strengthen predictive models for methane cycling in landfills and inform sustainable waste management strategies to curb methane emissions from solid waste.

microbiology↗

bioRxiv2022

MT-MAG: Accurate and interpretable machine learning based taxonomic assignment of metagenome-assembled genomes, with a partial classification option

We propose MT-MAG, a novel machine learning-based software tool for the complete or partial hierarchically-structured taxonomic classification of metagenome-assembled genomes (MAGs). MT-MAG is alignment-free, with k-mer frequencies being the only feature used to distinguish a DNA sequence from another (herein k = 7). MT-MAG is capable of classifying large and diverse metagenomic datasets: a total of 245.68 Gbp in the training sets, and 9.6 Gbp in the test sets analyzed in this study. In addition to complete classifications, MT-MAG offers a "partial classification" option, whereby a classification at a higher taxonomic level is provided for MAGs that cannot be classified to the Species level. MT-MAG outputs complete or partial classification paths, and interpretable numerical classification confidences of its classifications, at all taxonomic ranks. To assess the performance of MT-MAG, we define a "weighted classification accuracy," with a weighting scheme reflecting the fact that partial classifications at different ranks are not equally informative. For the two benchmarking datasets analyzed (genomes from human gut microbiome species, and bacterial and archaeal genomes assembled from cow rumen metagenomic sequences), MT-MAG achieves an average of 87.32% in weighted classification accuracy. At the Species level, MT-MAG outperforms DeepMicrobes, the only other comparable software tool, by an average of 34.79% in weighted classification accuracy. In addition, MT-MAG is able to completely classify an average of 67.70% of the sequences at the Species level, compared with DeepMicrobes which only classifies 47.45%. Moreover, MT-MAG provides additional information for sequences that it could not classify at the Species level, resulting in the partial or complete classification of 95.13%, of the genomes in the datasets analyzed. Lastly, unlike other taxonomic assignment tools (e.g., GDTB-Tk), MT-MAG is an alignment-free and genetic marker-free tool, able to provide additional bioinformatics analysis to confirm existing or tentative taxonomic assignments.

bioinformatics↗

bioRxiv2021

Cloacimonadota metabolisms include adaptations for engineered environments that are reflected in the evolutionary history of the phylum

Phylum Cloacimonadota (previously Cloacimonetes, WWE1) is an understudied bacterial lineage frequently associated with engineered and wastewater systems. Cloacimonadota members were abundant and diverse in metagenomic datasets from a municipal landfill, prompting an examination of phylogenetic relationships, metabolic diversity, and pangenomic dynamics across the phylum, based on 22 publicly available genomes and 24 from landfill samples. Cloacimonadota formed two discrete clades, with one clades genomes principally deriving from engineered systems. A few more-divergent genomes were placed basal in the tree, and not associated with either clade. Metabolic reconstructions for metagenome-assembled genomes predict an anaerobic, acetogenic, and fermentative lifestyle for the majority of Cloacimonadota surveyed. Genomes from engineered ecosystems (first clade) encode a unique suite of genes not typically found in genomes from natural environments (second clade). These encoded functions include acetate kinase, the enzyme responsible for the formation of acetate from acetyl phosphate, and carbon utilization enzymes, suggesting different substrate degradation and energy generation strategies in these ecologically and phylogenetically distinct lineages. Originality/Significance StatementCloacimonadota is a bacterial phylum that is under-described compared to its members prevalence in genome repositories. Cloacimonadota are frequently associated with engineered systems, including being identified as abundant and diverse in the municipal landfill site surveyed in this study. We reconstructed twenty-four landfill-associated Cloacimonadota metagenome assembled genomes (MAGs), more than doubling the number of publicly available Cloacimonadota genomes. We combined these MAGs with available reference genomes to predict major metabolic pathways and to describe the conserved features in the lifestyle of phylum Cloacimonadota. We found that Cloacimonadota have distinct evolutionary histories associated with engineered versus natural environments. Prior studies have evaluated metabolism from individual Cloacimonadota genomes - this work is the first to examine trait distribution across a more-complete representation of the phylum, including identification of genomic features and metabolic strategies that correlate to habitat of origin.

microbiology↗

bioRxiv2021

Adapting macroecology to microbiology: using occupancy modelling to assess functional profiles across metagenomes

Metagenomic sequencing provides information on the metabolic capacities and taxonomic affiliations for members of a microbial community. When assessing metabolic functions in a community, missing genes in pathways can occur in two ways: the genes may legitimately be missing from the community whose DNA was sequenced, or the genes were missed during shotgun sequencing or failed to assemble, and thus the metabolic capacity of interest is wrongly absent from the sequence data. Here, we borrow and adapt occupancy modelling from macroecology to provide mathematical context to metabolic predictions from metagenomes. We review the five assumptions underlying occupancy modelling through the lens of microbial community sequence data. Using the methane cycle, we apply occupancy modelling to examine the presence and absence of methanogenesis and methanotrophy genes from nearly 10,000 metagenomes spanning global environments. We determine that methanogenesis and methanotrophy are positively correlated across environments, and note that the lack of available standardized metadata for most metagenomes is a significant hindrance to large-scale statistical analyses. We present this adaptation of macroecologys occupancy modelling to metagenomics as a tool for assessing presence/absence of traits in environmental microbiological surveys. We further initiate a call for stronger metadata standards to accompany metagenome deposition, to enable robust statistical approaches in the future.

microbiology↗

bioRxiv2021

High diversity and heterogeneity define microbial communities across an active municipal landfill

Global waste production is increasing rapidly, with the majority of waste destined for landfills. Microbial communities in landfills transform waste and generate methane in an environment unique from other built and natural environments. Previous work has largely considered landfill microbial diversity only at the phylum level, identifying complex and variable communities. The extent of shared organismal diversity across landfills or over time and at more precise levels of classification remains unknown. We used 16S rRNA gene amplicon and metagenomic sequencing to examine the taxonomic and functional diversity of the microbial communities inhabiting a Southern Ontario landfill. The diversity of microbial populations in leachate and groundwater samples was correlated with geochemical conditions to determine drivers of microbial heterogeneity. Across the landfill, 25 bacterial and archaeal phyla were present at >1% relative abundance within at least one landfill sample. The Patescibacteria, Bacteroidota, Firmicutes, and Proteobacteria had the highest relative abundances, with most other phyla present at low (<5%) abundance. Below the phylum level, very few populations were identified at multiple sites, with only 121 of 8,030 populations present at five or more sites. This indicates that, although phylum-level signatures are conserved, individual landfill microbial populations vary widely. Significant differences in geochemistry occurred across the leachate and groundwater wells sampled, with calcium, iron, magnesium, boron, meta and para xylenes, ortho xylenes, and ethylbenzene concentrations contributing most strongly to observed site differences. This study illustrates that leachate microbial communities are much more complex and diverse within landfills than previously reported, with implications for waste management best practices.

microbiology↗

bioRxiv2020

The phylogenetic and global distribution of extracellular bioplastic degrading genes

Polyhydroxyalkanoates (PHAs) are a family of microbially-made polyesters commercialized as biodegradable plastics. PHA production rates are predicted to increase as concerns around environmental plastic contamination and limited fossil fuel resources have increased the importance of biodegradable and bio-based plastic alternatives. Microbially-produced PHA depolymerases are the key enzymes mediating PHA biodegradation, but only a few PHA depolymerases have been well-characterized and screens employing metagenomic sequence data are lacking. Here, we used 3,078 metagenomes to analyze the distribution of PHA depolymerases in microbial communities from diverse aquatic, terrestrial and waste management systems. We significantly expand the recognized diversity of this protein family by screening 1,914 Gb of sequence data and identifying 13,869 putative PHA depolymerases in 1,295 metagenomes. Our results indicate that PHA depolymerases are unevenly distributed across environments. We predicted the highest frequency of PHA depolymerases in wastewater systems and the lowest in marine and thermal springs. In tandem, we screened 5,290 metagenome-assembled genomes to describe the phylogenetic distribution of PHA depolymerases, which is substantially broader compared to current cultured representatives. The Proteobacteria and Bacteroidota are key lineages encoding PHA depolymerases, but PHA depolymerases were predicted from members of the Bdellovibrionota, Methylomirabilota, Actinobacteriota, Firmicutes, Spirochaetota, Desulfobacterota, Myxococcota and Planctomycetota. Originality/Significance StatementBiodegradable plastics like polyhydroxyalkanoates (PHAs) are a hot topic, following ubiquitous environmental plastic contamination, government bans on single-use plastics, and a growing need for sustainable alternatives to petroleum-based plastics. Understanding the microbial conversion of PHAs in the environment and finding biomolecular tools that can act on PHAs is increasingly important as PHAs grow in popularity. In this study, we screened thousands of metagenomes and metagenome-assembled genomes (MAGs) to substantially increase the recognized diversity of PHA depolymerases, the key enzymes mediating PHA biodegradation. We use datasets from seven continents to provide a global summary of the distribution of PHA depolymerase genes in natural environments and waste-management systems. In tandem, we increase the number of described phylum-level lineages with PHA biodegradation potential. This work contributes a new understanding of the phylogenetic and environmental distribution of PHA depolymerases.

microbiology↗

bioRxiv2020

Composition of the North American wood frog (Rana sylvatica) skin microbiome and seasonal variation in community structure

While a number of amphibian microbiomes have been characterized, it is unclear how microbial communities might vary in response to seasonal changes in the environment and the behaviors which many amphibians exhibit. Given recent studies demonstrating the importance of the skin microbiome in frog innate immune defenses against pathogens, investigating how changes in the environment impact the microbial species present, and thus their potential contribution to skin host defense, will provide a better understanding of conditions that may alter host susceptibility to pathogens in their environment. We sampled the skin microbiome of North American wood frogs (Rana sylvatica) from two breeding ponds in the spring, along with the microbial community present in their vernal breeding pools, and frogs from the nearby forest floor in the summer and fall to determine whether the microbial composition differs by sex, vernal pond site, or temporally across season (spring, summer, fall). Taxon abundance data reveals a profile of bacterial phyla similar to those previously described on anuran skin, with Proteobacteria, Bacteroidetes, and Actinobacteria dominating the wood frog skin microbiome. Our results indicate that sex had no significant effect on skin microbiota diversity, however, this may be due to our limited female sample size. Vernal pool site had a small but significant effect on skin microbiota, but skin-associated communities were more similar to each other than to the communities observed in the frogs respective pond water. Across seasons, diversity analyses suggest there are significant differences between the skin microbiome of frogs from spring and summer/fall groups while the average -diversity per frog remained consistent. Bacterial genera known to have antifungal properties such as Pseudomonas spp. and Rhizobium spp. were prevalent, and several were considered core microbiota during at least one season. These results illustrate seasonal variation in wood frog skin microbiome structure and highlight the importance of considering temporal trends in an amphibian microbiome, particularly for species whose life history requires recurrent shifts in habitat and behavior.

microbiology↗