Editorial:Exploring the combined effect of climate change and pollution on freshwater ecosystems

ISSN:2296-665

Impact of Environmental Disturbances on Aquatic Microbial Community Structure and Function

Despite their small share of Earth’s surface, freshwater ecosystems contribute significantly to regional and global carbon budgets. Bacterial communities in these ecosystems play a fundamental role in the the biogeochemical flux and food web dynamics. However, our understanding of how aquatic bacterial communities respond to changes in nutrient regimes and substrate availability arising from perturbations in their environment is limited. My research described herein focuses on investigating the impact of environmental disturbances on bacterial community dynamics in regionally important aquatic ecosystems. First, an evaluation of short-term impacts of stormflow events on the bacterial community of a highly urbanized stream of the Chicago Area Waterways (CAWS) was performed. Using 16S rRNA gene sequencing and metagenomics, assessment of the stream bacterial community composition and functional potential during dry and wet weather demonstrated the influence of increased wastewater treatment plant effluent flow following rain in shifting the stream bacterial community from abundant freshwater taxa to those more associated with anthropogenic settings. Shifts in taxonomic composition were also linked to changes in the functional gene content. Next, I evaluated bacterial community dynamics and carbon metabolism in southern Lake Michigan in light of the of the recent ecological changes in the lake due to the invasive dreissenid mussels. Bacterial community diversity, gene content and gene expression patterns in nearshore and offshore Lake Michigan and community response to a pulse of terrestrially derived DOM (t-DOM) was investigated using metagenomics and metatranscriptomics. Results highlighted overall similarities in the bacterial communities of the oligotrophic offshore and the more productive nearshore, except for differences in the relative abundance of genes/gene transcripts affiliated with Cyanobacteria and the taxonomic composition of DOM transporter gene transcripts. However, both nearshore and offshore bacterial communities responded similarly to the t-DOM pulse, in the form of increased transcription for aromatic compound metabolism. Overall, the results of these studies demonstrate sensitivity of aquatic bacterial community structure and gene content to short-term perturbations as seen in CAWS, but a potential resilience in community function (carbon metabolism) to long-term stressors such as the invasive mussels in Lake Michigan

Taxon-Driven Functional Shifts Associated with Storm Flow in an Urban Stream Microbial Community

Urban streams in various parts of the world are facing increased anthropogenic pressure on their water quality, and storm flow events represent one such source of complex physical, chemical, and biological perturbations. Microorganisms are important components of these streams from both ecological and public health perspectives. Analysis of the effect of perturbations on the stream microbial community can help improve current knowledge on the impact such chronic disturbances can have on these water resources. This study examines microbial community dynamics during rain-induced storm flow conditions in an urban stream of the Chicago Area Waterway System. Additionally, using shotgun metagenomics we identified significant shifts in the microbial community composition and functional gene content following a high-rainfall event, with potential environment and public health implications. Previous work in this area has focused on specific genes/organisms or has not assessed immediate storm flow impact.Urban streams are susceptible to stormwater and sewage inputs that can impact their ecological health and water quality. Microbial communities in streams play important functional roles, and their composition and metabolic potential can help assess ecological state and water quality. Although these environments are highly heterogenous, little is known about the influence of isolated perturbations, such as those resulting from rain events on urban stream microbiota. Here, we examined the microbial community composition and diversity in an urban stream during dry and wet weather conditions with both 16S rRNA gene sequencing across multiple years and shotgun metagenomics to more deeply analyze a single storm flow event. Metagenomics was used to assess population-level dynamics as well as shifts in the microbial community taxonomic profile and functional potential before and after a substantial rainfall. The results demonstrated general trends present in the stream under storm flow versus base flow conditions and also highlighted the influence of increased effluent flow following rain in shifting the stream microbial community from abundant freshwater taxa to those more associated with urban/anthropogenic settings. Shifts in the taxonomic composition were also linked to changes in functional gene content, particularly for transmembrane transport and organic substance biosynthesis. We also observed an increase in relative abundance of genes encoding degradation of organic pollutants and antibiotic resistance after rain. Overall, this study highlighted some differences in the microbial community of an urban stream under storm flow conditions and showed the impact of a storm flow event on the microbiome from an environmental and public health perspective