Examining Shifts in Stream Microbial Communities Exposed to Oil and Gas Wastewaters Completed

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U.S. Geological Survey (USGS) researchers studied the potential pathways of unconventional oil and gas (UOG) wastewaters into the environment to determine if there were effects on exposed organisms. UOG wastewaters consist of complex chemical mixtures including high total dissolved solids, naturally occurring radioactive materials, organic and heavy metal compounds, and additives such as biocides used in hydraulic fracturing fluids to control corrosion, souring, and biofouling.

Based on ongoing work, USGS and Rutgers University scientists expected that the complex chemical mixtures in UOG wastewater could promote changes in the composition of exposed microbial communities including shifts to antimicrobial resistant bacteria due to the use of biocides. Scientists assessed microbial community composition in stream water and sediment samples from Wolf Creek upstream and downstream from a West Virginia UOG wastewater injection well disposal site. To accomplish this, molecular (DNA-based) methods were applied to sediment and water samples to profile antibiotic-resistance genes, profile the microbial community structure, and describe microbial community functional potential.

Shifts in the overall microbial community structure were measured in stream sediments that contained chemicals associated with UOG wastewaters. In particular, signatures for spore formation, dormancy, and methanogenesis were elevated in the impacted sediments. These shifts indicate that microbial communities responded to environmental disturbances, which in this study were characterized by previously described shifts in geochemistry. The relative abundance of total antibiotic-resistance genes was similar in background and downstream sediments. This similarity is not totally unexpected because antibiotic resistance is naturally present in many environments, predating the use of antibiotics, partly because antibiotics in use today are produced by microbes. There were higher relative abundances of two genes encoding for multidrug resistance (acrB and mexB) in sediments downstream from the UOG facility even in the absence of measured biocides. The higher relative abundance of acrB and mexB is likely due to their function as efflux pumps to help remove foreign chemicals as well as antibiotics from cells. For context, the relative abundances of total antibiotic resistance genes measured in this study were lower than those reported for municipal wastewater, which is considered to be on the high end of expected resistance gene abundance.

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Microorganisms are vital parts of stream ecosystems. Microbial community structure shifted at sites downstream of UOG wastewaters leaving questions about the affect these shifts have on nutrient cycling and other key processes.

The USGS Environmental Health Program (Toxic Substances Hydrology and Contaminant Biology) of the Ecosystems Mission Area funded this study, as well as a research stipend to Hannah Delos Reyes from the Douglass Project, a graduate fellowship to Alessia Eramo from Rutgers University School of Engineering, and Nicole L. Fahrenfeld Rutgers University startup funds.