Aerosol viruses released from the melting cryosphere: sentinel microorganisms in a changing Arctic
Part of Sentinel North thematic project #3
Viruses play a major role in controlling biodiversity and ecology of aquatic microbial communities. They control their hosts’ evolution by allowing genetic exchange, induce significant mortality in the prokaryotic biomass, and control ecosystem’s productivity by redirecting carbon into the microbial loop.
The arctic cryosphere is a reservoir for such viruses. Indeed, glaciers and permafrost, with their freeze-thaw cycles, can release viral particles that have been trapped in ice for thousands of years, recycling their genomes into modern environments. These viruses can be released into the atmosphere and recolonize aquatic ecosystems of the arctic landscape or include pathogens that could impact human health in the North. Climate change has accelerated permafrost and glacier thawing, increasing humidity and leading to greater aerosolization from water, which could increase the amount of viruses in the air and their potential dispersion in the landscape.
The “aerosol virome”, the atmospheric viral community, has long been studied in hospitals, as it can influence transmission of infectious diseases. However, few studies have focused on environmental aerosol viromes, and none have explored viruses that can be released into the atmosphere from thawing glaciers and permafrost. This is of major importance in ecology, as this recycling of newly released viral genomes could allow for a new colonization of the Arctic. This could have consequences on human health in the North, and on ecosystem productivity and nutrient transfer.
The goal of my project is to describe environmental viral aerosols in the North, and to determine how the thawing of the cryosphere contributes to the release and dispersion of viruses across the landscape.
Mercury in the Arctic, from the environment to human health: dietary bioaccessibility and interactions with the human gut microbiome
Co-supervised by B. Jesse Shapiro, Microbial Evolutionary Genomics Lab
Mercury (Hg) is a contaminant of major interest in the Arctic, both for human and ecosystem health. Produced at industrialized latitudes by human activity, Hg is easily carried to the Arctic. It can then be deposited in the North and accumulate in aquatic ecosystems, where it can be transformed into its organic and toxic form of methylmercury (MeHg). As MeHg can biomagnify through foodwebs, it can have important health consequences on the Inuit, whose traditional diet relies on fauna that can be contaminated.
Guidelines aiming to protect consumers from Hg assume that 100% of MeHg in fish is absorbed by the human body, but recent studies suggest this may be an overestimate. Indeed, these recommendations do not take into account dietary practices, which may alter speciation and complexation of MeHg, changing the way it is absorbed. We used an in vitro digestion model to study the impact of dietary practices on bioaccessibility (the fraction of a contaminant solubilized in the gastrointestinal tract) of MeHg. Our results show that cooking and co-ingesting polyphenol-rich foods (such as tea) can significantly reduce bioaccessibility, and both treatments can have a cumulative effect. While this in vitro study must be validated in an in vivo model, it improves our understanding of the mechanistic fate of Hg in the body, and offers novel ways of improving current guidelines.
Another variable that could potentially affect how MeHg behaves in the human body is the gut microbiome, the complex microbial ecosystem that colonizes the human intestine. Since microorganisms are the drivers of biogeochemical cycling of Hg in the environment, it is possible bacterial members of the microbiome can interact with Hg and MeHg ingested with food, notably in the Inuit who are exposed to MeHg through their traditional diet. Here, we provide the first description of the Inuit microbiome using next generation sequencing of a marker gene. We show that the taxonomic composition and diversity of the Inuit microbiome is broadly similar to that of Westerners, likely due to the dietary transition currently underway in Northern communities. However, using fine-scale strain-level analyses, we identified many markers associated with the traditional Inuit diet. Using shotgun metagenomic sequencing, we also present the first functional profile of the Inuit microbiome, and show that mobile genes such as plasmids have a unique signature in the Inuit, and investigated the presence of mercury-metabolism genes in the microbiome.
Girard et al. (2018) Sci. Tot. Environ. 616-617:863-874, doi:10.1016/j.scitotenv.2017.10.236.
Dubois et al. (2017) Microbiome, 5:151, doi:10.1186/s40168-017-0370-7.
Girard et al. (2017) mSphere 2(1):e00297-16, doi:10.1128/mSphere.00297-16.
Distribution of mercury in Arctic freshwater ecosystems and photodemethylation of methylmercury
Supervised by Marc Amyot, Global Change & Ecotoxicology Lab
Photodemethylation of MeHg is an abiotic process occurring in aquatic ecosystems that degrades MeHg into the less toxic Hg. Our results from Arctic freshwater ecosystems show that while photodemethylation occurs in permafrost thaw ponds, it is barely detectable in Arctic oligotrophic lakes. This contradicts the commonly accepted idea that photodemethylation is ubiquitous in aquatic ecosystems, and we hypothesized that the lack of organic matter in oligotrophic lakes may explain this difference. Finally, by manipulating an entire pond, we show that photodemethylation did not impact this small ecosystem’s net MeHg budget. However, we suggest that the importance of photodemethylation may change with increased input of organic matter and Hg into thaw ponds due to climate warming.
Girard et al. (2016) Environ. Sci. Technol., 50(7):3511-3520, doi:10.1021/acs.est.5b04921.
MacMillan G. et al. (2015) Environ. Sci. Technol. 49(13):7743-7753, doi:10.1021/acs.est.5b00763.
Braune B. et al. (2014) Sci. Tot. Environ. 509:68-90, doi: 10.1016/j.scitotenv.2014.05.133.
Chételat et al. (2014) Sci. Tot. Environ., 509:41-66, doi:10.1016/j.scitotenv.2014.05.151.
Neonicotinoid metabolism by honey bee gut microbiome
Supervised by Nancy Moran at the University of Texas at Austin
Neonicotinoids (such as imidacloprid) are among the most extensively used insecticides, and are applied by spraying or as a prophylactic treatment by seed dressing. Imidacloprid traces can therefore be found in pollen or nectar of treated plants, and this may have unintended negative effects on pollinators such as bees. These impacts include impeded larval growth, neurotoxicity symptoms and mortality. Once in the environment, the fate of imidacloprid is not static: we know that certain microorganisms can metabolize imidacloprid, altering its toxicity. This is important to understand, as some products of the degradation of imidacloprid are even more toxic than the insecticide itself.
Impacts of neonicotinoids on bee performance are a major economic concern, as these pollinators are a major actor in maintaining agricultural productivity worldwide.
We know that bees possess many natural symbionts, including an intestinal microbiota containing different bacterial groups. The composition of this microbiota appears to be consistent amongst individual bees and across populations in different areas of the world, suggesting that these bacteria play a key role in bee biology. Indeed, these bacteria may have metabolic functions that contribute to host health. If this microbial metabolism includes biotransformation pathways for imidacloprid, it is possible that the insecticide could be made more or less toxic in the bee gut. This would have significant impacts on the health of honey bees in areas where imidacloprid is used.
During my Fulbright doctoral fellowship at UT Austin, I investigated the metabolism of neonicotinoid insecticides by the honey bee gut microbiome, and attempted to determine if degradation was possible by these symbionts via metabolite detection by LC/MS.
Raymann K. et al (2018) Appl. Environ. Microbiol., 00545-18, doi:10.1128/AEM.00545-18.