David A Walsh

David A Walsh
Concordia University Montreal · Department of Biology

PhD

About

44
Publications
8,236
Reads
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1,124
Citations
Citations since 2017
32 Research Items
762 Citations
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2017201820192020202120222023050100150200
2017201820192020202120222023050100150200

Publications

Publications (44)
Article
Full-text available
Lakes are sentinels of environmental changes within their watersheds including those induced by a changing climate and anthropogenic activities. In particular, contamination originating from point or non-point sources (NPS) within watersheds might be reflected in changes in the bacterial composition of lake water. We assessed the abundance of poten...
Article
Full-text available
Mercury (Hg) methylation genes (hgcAB) mediate the formation of the toxic methylmercury and have been identified from diverse environments, including freshwater and marine ecosystems, Arctic permafrost, forest and paddy soils, coal‐ash amended sediments, chlor‐alkali plants discharges and geothermal springs. Here we present the first attempt at a s...
Article
Full-text available
Background The Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to d...
Article
Full-text available
High-throughput RNA sequencing offers broad opportunities to explore the Earth RNA virome. Mining 5,150 diverse metatranscriptomes uncovered >2.5 million RNA virus contigs. Analysis of >330,000 RNA-dependent RNA polymerases (RdRPs) shows that this expansion corresponds to a 5-fold increase of the known RNA virus diversity. Gene content analysis rev...
Poster
Biodiversity surveys can be substantially improved through the analysis of environmental DNA (eDNA) if appropriate DNA sequence reference databases exist. Here, we aimed to assess the availability of molecular genetic resources for Canada’s freshwater-dependent species and identify data deficiencies where future research should be directed. The mai...
Preprint
Full-text available
Background The Arctic Ocean receives massive freshwater input and a correspondingly large amount of humic-rich organic matter of terrestrial origin. Global warming, permafrost melt, and a changing hydrological cycle will contribute to an intensification of terrestrial organic matter release to the Arctic Ocean. Although considered recalcitrant to d...
Preprint
Full-text available
Lakes are highly heterogenous ecosystems inhabited by a rich microbiome whose genomic diversity remains poorly defined compared to other major biomes. Here, we present a continental-scale study of metagenomes collected across one of the most lake-rich landscapes on Earth. Analysis of 308 Canadian lakes resulted in a metagenome-assembled genome (MAG...
Preprint
Our decreasing ability to fight bacterial infections is a major health concern. It is arising due to the evolution of antimicrobial resistance (AMR) in response to the mis- and overuse of antibiotics in both human and veterinary medicine. Lakes integrate watershed processes and thus may act as receptors and reservoirs of antibiotic resistance genes...
Article
Full-text available
Molecular genetic approaches applied to environmental DNA have great potential for biodiversity research and ecosystem monitoring. A metagenome is produced via shotgun sequencing of DNA collected directly from the environment and represents a sample of genetic information from all organisms captured in an environmental sample. Metagenomes have been...
Article
Full-text available
Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers, and symbionts. However, a comprehensive view of protist diversity in freshwaters has been challenged by the immense environmental heterogeneity among lakes worldwide. We assessed protist diversity in the surface waters of 366 freshwater lakes across a...
Presentation
Waterborne diseases are a major source of mortality in the world with more than 2.2 million deaths per year and even more morbidity cases every day. Some of the most serious infections such as cholera provoke humanitarian crises in regions most in need of health resources and clean water supplies. However, deaths attributed to waterborne diseases a...
Preprint
Full-text available
Protists play key roles in aquatic food webs as primary producers, predators, nutrient recyclers, and symbionts. Yet, a comprehensive view of protist diversity in freshwaters has been challenged by the immense environmental heterogeneity among lakes worldwide. We assessed protist diversity in the surface waters of 366 freshwater lakes across a nort...
Preprint
Full-text available
Mercury methylation genes (hgcAB) mediate the formation of the toxic methylmercury and have been identified from diverse environments, including freshwater and marine ecosystems, Arctic permafrost, forest and paddy soils, coal-ash amended sediments, chlor-alkali plants discharges and geothermal springs. Here we present the first attempt at a standa...
Poster
Full-text available
Microbes carrying the hgcAB gene pair are primarily responsible for methylmercury (MeHg) production, transforming inorganic mercury (HgII) into MeHg. Recent work based on the detection of hgcAB genes in publicly available genomic data and metagenome-assembled genomes expanded our understanding of the phylogenetic diversity of potential Hg-methylato...
Article
Accurately identifying the species present in an ecosystem is vital to lake managers and successful bioassessment programs. This is particularly important when monitoring cyanobacteria, as numerous taxa produce toxins and can have major negative impacts on aquatic ecosystems. Increasingly, DNA-based techniques such as meta- barcoding are being used...
Article
Full-text available
Eukaryotic pathogens including fungi and enteroparasites infect humans, animals and plants. As integrators of landscape catchment, lakes can reflect and record biological and geochemical events or anthropogenic changes and provide useful knowledge to formulate public health, food security and water policies to manage and prevent diseases. In this c...
Preprint
Full-text available
Molecular genetic approaches applied to environmental DNA have great potential for biodiversity research and ecosystem monitoring. A metagenome contains genetic information from all organisms captured in an environmental sample. It has been primarily used to study bacteria and archaea, but promising reports focusing on metazoan diversity are emergi...
Article
Full-text available
Global warming is profoundly influencing the Arctic Ocean. Rapid ice melt and increased freshwater input is increasing ocean stratification, driving shifts in nutrient availability and the primary production that supports marine food webs.
Article
Full-text available
Microbial sulfur metabolism contributes to biogeochemical cycling on global scales. Sulfur metabolizing microbes are infected by phages that can encode auxiliary metabolic genes (AMGs) to alter sulfur metabolism within host cells but remain poorly characterized. Here we identified 191 phages derived from twelve environments that encoded 227 AMGs fo...
Conference Paper
Full-text available
Since the seminal paper in 1998 (Coolen and Overmann), sedimentary ancient DNA (sedaDNA) has become a powerful tool in paleoecology to reconstruct past changes in terrestrial and aquatic biodiversity. Still, sedaDNA is an emerging tool and there is a need for calibrations and validations to ensure the reliability of sedaDNA as a proxy to reconstruc...
Preprint
Full-text available
We study the microbiome of sea water collected from two locations of the Barbadian coral reefs. The two sites differ in several environmental and ecological variables including their endogenous benthic community in addition to their proximity to urban development and runoffs from inland watersheds. The composition of the microbial community was est...
Article
Full-text available
The reconstruction of ecological time series from lake sediment archives can retrace the environmental impact of human activities. Molecular genetic approaches in paleolimnology have provided unprecedented access to DNA time series, which record evidence of the microbial ecologies that underlaid historical lake ecosystems. Such studies often rely o...
Preprint
Full-text available
Lakes play a pivotal role in ecological and biogeochemical processes and have been described as ‘sentinels’ of environmental change. Assessing ‘lake health’ across large geographic scales is critical to predict the stability of their ecosystem services and their vulnerability to anthropogenic disturbances. The LakePulse research network is tasked w...
Article
The Arctic Ocean is relatively isolated from other oceans and consists of strongly stratified water masses with distinct histories, nutrient, temperature, and salinity characteristics, therefore providing an optimal environment to investigate local adaptation. The globally distributed SAR11 bacterial group consists of multiple ecotypes that are ass...
Article
Full-text available
The distribution and quality of water resources vary dramatically across Canada, and human impacts such as land-use and climate changes are exacerbating uncertainties in water supply and security. At the national level, Canada has no enforceable standards for safe drinking water and no comprehensive water-monitoring program to provide detailed, tim...
Article
Full-text available
In Table 3 of this Data Descriptor the units of Mean_N2O and Mean_CH4 are incorrectly stated as “Nanomolar (μM)”. This should instead read “Nanomolar (nM)”.
Preprint
Full-text available
The Arctic Ocean is relatively isolated from other oceans and consists of strongly stratified water masses with distinct histories, nutrient, temperature and salinity characteristics, therefore providing an optimal environment to investigate local adaptation. The globally distributed SAR11 bacterial group consists of multiple ecotypes that are asso...
Article
Northern lakes are ice‐covered for a large part of the year, yet our understanding of microbial diversity and activity during winter lags behind that of the ice‐free period. In this study, we investigated under‐ice diversity and metabolism of Verrucomicrobia in seasonally ice‐covered lakes in temperate and boreal regions of Quebec, Canada using 16S...
Article
Full-text available
Meta-omic technologies such as metagenomics, metatranscriptomics and metaproteomics can aid in the understanding of microbial community structure and metabolism. Although powerful, metagenomics alone can only elucidate functional potential. On the other hand, metaproteomics enables the description of the expressed in situ metabolism and function of...
Article
Biodiversity currently faces unprecedented threats owing to species extinctions. Ecologically, compensatory dynamics can ensure stable community biomass following perturbation. However, whether there is a contribution of genetic diversity to community responses is an outstanding question. To date, the contribution of evolutionary processes through...
Article
Full-text available
The diversity and distribution of methylotrophic bacteria has been investigated in the ocean and lakes using the methanol dehydrogenase mxaF gene as a functional marker. However, pelagic marine (OM43) and freshwater (LD28 and PRD01a001B) methylotrophs within the Beta-proteobacteria lack mxaF, instead possessing a related xoxF4-encoded methanol dehy...
Article
Here we harnessed the power of metaproteomics to assess the metabolic diversity and function of stratified aquatic microbial communities in the deep and expansive Lower St. Lawrence Estuary, located in Eastern Canada. Vertical profiling of the microbial communities through the stratified water column revealed differences in metabolic lifestyles and...
Article
Full-text available
Microbiome samples often represent mixtures of communities, where each community is composed of overlapping assemblages of species. Such mixtures are complex, the number of species is huge and abundance information for many species is often sparse. Classical methods have a limited value for identifying complex features within such data. Here, we de...
Article
Temperate oceans are inhabited by diverse and temporally dynamic bacterioplankton communities. However, the role of the environment, resources and phytoplankton dynamics in shaping marine bacterioplankton communities at different time scales remains poorly constrained. Here, we combined time-series observations (time scales of weeks to years) with...
Article
Full-text available
In this study, we used comparative metaproteomics to investigate the metabolic activity of microbial plankton inhabiting a seasonally hypoxic basin in the Northwest Atlantic Ocean (Bedford Basin). From winter to spring, we observed a seasonal increase in high-affinity membrane transport proteins involved in scavenging of organic substrates; Rhodoba...
Article
Bacteria are ubiquitous and important members of aquatic ecosystems ranging from inland lakes to the open ocean. Since the advent of molecular approaches for investigating bacteria community composition (BCC), the biogeography of aquatic bacteria has been investigated across a wide variety of environments. In addition to illuminating important aspe...
Article
Full-text available
Life in Dead Zones Oxygen minimum zones, or oceanic “dead zones,” are expanding. Marine dead zone expansion and intensification results in amplification of biological nitrogen and greenhouse gas production, with implications for marine fisheries' productivity and for climate balance. Little is known about the microbial communities mediating the und...
Article
Full-text available
Dissolved oxygen concentration plays a major role in shaping biotic interactions and nutrient flows within marine ecosystems. Throughout the global ocean, regions of low dissolved oxygen concentration (hypoxia) are a common and expanding feature of the water column, with major feedback on productivity and greenhouse gas cycling. To better understan...

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Projects

Project (1)
Project
The NSERC Canadian Lake Pulse Network is a scientific initiative on environmental issues affecting Canadian lakes. It brings together experts in lake science, spatial modelling, analytical chemistry, public health, remote sensing, amongst others. The impacts of land-use changes, climate change and contaminants are assessed while developing new tools for lake stewardship.