Using testate amoeba as potential biointegrators of atmospheric deposition of phenanthrene (polycyclic aromatic hydrocarbon) on "moss/soil interface-testate amoeba community" microecosystems

Interactions between soil protists and pollutants: An unsolved puzzle

Soil protists are essential but often overlooked in soils, although they play crucial functional roles in the terrestrial ecosystem. While soil protists have drawn increased attention to their functional role in soils, their interaction with soil pollutants remains unresolved. This review provides a first overview of the current understanding of interactions between soil protists and major pollutants (heavy metals, organic pollutants, nanoparticles, and soil pathogens). We summarize how soil pollutants affect protists and vice versa, showing that we are just beginning to understand their complex interactions. In addition, we identify five research gaps, including hidden diversity, adaptive mechanisms, species interactions, soil bioindicators and environmental applications, and we hope that our review will help promote and build research guidelines for the future. In conclusion, a better understanding of soil pollutant-protist interactions will significantly increase our knowledge of the pollution ecology in the soil and how soil organisms respond and adapt to environmental pollution, which will contribute to the bioremediation and environmental applications of protists in soil.

Assessing the responses of Sphagnum micro-eukaryotes to climate changes using high throughput sequencing

Current projections suggest that climate warming will be accompanied by more frequent and severe drought events. Peatlands store ca. one third of the world's soil organic carbon. Warming and drought may cause peatlands to become carbon sources through stimulation of microbial activity increasing ecosystem respiration, with positive feedback effect on global warming. Micro-eukaryotes play a key role in the carbon cycle through food web interactions and therefore, alterations in their community structure and diversity may affect ecosystem functioning and could reflect these changes. We assessed the diversity and community composition of Sphagnum-associated eukaryotic microorganisms inhabiting peatlands and their response to experimental drought and warming using high throughput sequencing of environmental DNA. Under drier conditions, micro-eukaryotic diversity decreased, the relative abundance of autotrophs increased and that of osmotrophs (including Fungi and Peronosporomycetes) decreased. Furthermore, we identified climate change indicators that could be used as early indicators of change in peatland microbial communities and ecosystem functioning. The changes we observed indicate a shift towards a more "terrestrial" community in response to drought, in line with observed changes in the functioning of the ecosystem.

Microbial Eukaryotes in Oil Sands Environments: Heterotrophs in the Spotlight

Hydrocarbon extraction and exploitation is a global, trillion-dollar industry. However, for decades it has also been known that fossil fuel usage is environmentally detrimental; the burning of hydrocarbons results in climate change, and environmental damage during extraction and transport can also occur. Substantial global efforts into mitigating this environmental disruption are underway. The global petroleum industry is moving more and more into exploiting unconventional oil reserves, such as oil sands and shale oil. The Albertan oil sands are one example of unconventional oil reserves; this mixture of sand and heavy bitumen lying under the boreal forest of Northern Alberta represent one of the world’s largest hydrocarbon reserves, but extraction also requires the disturbance of a delicate northern ecosystem. Considerable effort is being made by various stakeholders to mitigate environmental impact and reclaim anthropogenically disturbed environments associated with oil sand extraction. In this review, we discuss the eukaryotic microbial communities associated with the boreal ecosystem and how this is affected by hydrocarbon extraction, with a particular emphasis on the reclamation of tailings ponds, where oil sands extraction waste is stored. Microbial eukaryotes, or protists, are an essential part of every global ecosystem, but our understanding of how they affect reclamation is limited due to our fledgling understanding of these organisms in anthropogenically hydrocarbon-associated environments and the difficulties of studying them. We advocate for an environmental DNA sequencing-based approach to determine the microbial communities of oil sands associated environments, and the importance of studying the heterotrophic components of these environments to gain a full understanding of how these environments operate and thus how they can be integrated with the natural watersheds of the region.

To what extent do food preferences explain the trophic position of heterotrophic and mixotrophic microbial consumers in a Sphagnum peatland?

Although microorganisms are the primary drivers of biogeochemical cycles, the structure and functioning of microbial food webs are poorly studied. This is the case in Sphagnum peatlands, where microbial communities play a key role in the global carbon cycle. Here, we explored the structure of the microbial food web from a Sphagnum peatland by analyzing (1) the density and biomass of different microbial functional groups, (2) the natural stable isotope (δ(13)C and δ(15)N) signatures of key microbial consumers (testate amoebae), and (3) the digestive vacuole contents of Hyalosphenia papilio, the dominant testate amoeba species in our system. Our results showed that the feeding type of testate amoeba species (bacterivory, algivory, or both) translates into their trophic position as assessed by isotopic signatures. Our study further demonstrates, for H. papilio, the energetic benefits of mixotrophy when the density of its preferential prey is low. Overall, our results show that testate amoebae occupy different trophic levels within the microbial food web, depending on their feeding behavior, the density of their food resources, and their metabolism (i.e., mixotrophy vs. heterotrophy). Combined analyses of predation, community structure, and stable isotopes now allow the structure of microbial food webs to be more completely described, which should lead to improved models of microbial community function.

Exposure chambers for studying the partitioning of atmospheric PAHs in environmental compartments: validation and calibration using experimental and computational approaches

The environmental partitioning of atmospheric polycyclic aromatic hydrocarbons (PAHs) conditions their entry into food chains and subsequent risks for human health. The need for new experimental exposure devices for elucidating the mechanisms governing ecosystemic PAH transfer motivated the elaboration of an original small-scale exposure chamber (EC). A dual approach pairing experimentation and computational fluid dynamics (CFD) was selected to provide comprehensive validation of this EC as a tool to study the transfer and biological effects of atmospheric PAH pollution in microsystems. Soil samples and passive air samplers (PASs) were exposed to atmospheric pollution by phenanthrene (PHE), a gaseous PAH, for 2 weeks in examples of the EC being tested, set up under different conditions. Dynamic concentrations of atmospheric PHE and its uptake by PASs were simulated with CFD, results showing homogeneous distribution and constant atmospheric PHE concentrations inside the ECs. This work provides insight into the setting of given concentrations and pollution levels when using such ECs. The combination of experimentation and CFD is a successful ECs calibration method that should be developed with other semivolatile organic pollutants, including those that tend to partition in the aerosol phase.