The host microbiome (mainly bacteria) is essential for host immune function, metabolism, and digestion. Alterations in these microbes, known as dysbiosis, generally results in adverse effects to the host, including diseases. Dysbiosis can be induced from exposures to various anthropogenic contaminants including constituents of municipal wastewater treatment effluents (MWWEs), namely, pharmaceuticals, antibiotics, and excess nutrients. Despite MWWEs being one of the largest dischargers to aquatic ecosystems, impacts of these contaminants on exposed organism microbiomes, especially in aquatic insects, is unclear. In addition, some aquatic contaminants may transfer to riparian habitats through predation on emergent insects that were exposed to contaminants as larvae, and subsequently alter microbiomes of terrestrial predators. Our study evaluated whether MWWEs altered microbiomes of freshwater larval and adult insects and their riparian spider predators using effluent-associated bacteria and stable nitrogen isotopes (δ15N) to confirm effluent exposure. We analyzed microbiome compositions through sequencing of the V3-V4 hypervariable region of the 16S rRNA gene and analyzed food web dynamics with stable carbon (δ13C) and nitrogen (δ15N) isotopes. We found that insects and spiders were enriched in δ15N at one site downstream of wastewater outfalls, indicating exposure to effluents and transfer of nutrients to terrestrial ecosystems. Microbiomes of most larval and adult insects were altered downstream of wastewater outfalls and had lower relative abundances of endosymbiont bacteria, shifts in bacterial diversities, increases in abundances of effluent-associated bacteria, and downregulation of some biosynthesis pathways than those collected at upstream sites. However, spider microbiomes had little evidence of dysbiosis, and were distinct from those of adult insects, despite a close association in their isotopic signatures. Overall, this study provides evidence of biological impacts from MWWEs to exposed insects and suggests that changes in microbial communities of invertebrates may be used as an effective indicator of effluent exposure as part of monitoring frameworks. / Thesis / Master of Science (MSc) / Municipal wastewater treatment facilities release contaminants into aquatic ecosystems that may affect the health of exposed organisms, including their microbiome, which contains bacteria essential for host digestion and immune function. Alterations in microbiomes of contaminant-exposed aquatic insects are poorly characterized and such effects may be transferred to terrestrial ecosystems through emergent insects. This study evaluated microbiomes and food web dynamics of freshwater insects and riparian spiders upstream and downstream of wastewater treatment facilities in the Bow River, AB. Results indicate that microbiomes of some downstream aquatic insects had lower relative abundances of endosymbiont bacteria, shifts in bacterial diversities, and increases in abundances of effluent-associated bacteria than those collected at upstream sites, but no such changes were observed in the spider predators. This study improves our understanding of how freshwater insect microbiomes are altered by municipal wastewater effluents and suggests that directly effluent-exposed organisms are more at risk of dysbiosis.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/29714 |
| Date | January 2024 |
| Creators | Diesbourg, Emilie |
| Contributors | Kidd, Karen, Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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