Urban streams are impacted simultaneously by a variety of anthropogenic disturbances, such as altered hydrology, input of organic and inorganic compounds (nutrients, pharmaceuticals, metals, etc.), and influx of microorganisms. Microorganisms are central members of the stream community and contribute to key ecosystem functions. In this study, we examined the microbial ecology of a model urban stream: Tinker’s Creek, a seventh order stream and the largest tributary of the Cuyahoga River (NE OH, USA). Tinker’s Creek traverses a rural to urban landscape and hosts eight wastewater treatment plants with significant discharges. In this study, we examined benthic and macroinvertebrate-associated bacterial communities at five study sites along this longitudinal gradient (2 nearby streams served as reference sites) and related it to physicochemical conditions. We also examined the occurrence of antibiotic resistance genes (ARGs). Macroinvertebrates were examined based on taxon and functional feeding group. DNA was extracted from environmental samples and subjected to Illumina sequencing (and analysis at the amplicon sequence variant level (ASV) with QIIME 2) to determine community composition while ARG abundance (for tetracycline and sulfonamide) was determined with quantitative PCR.
Results/Conclusions
There were significant differences in benthic bacterial communities among sites and among macroinvertebrate taxa. The gut bacterial community of macroinvertebrates demonstrated consistency among taxa more so than among sites and differed from benthic bacterial communities. Specifically, redundancy analysis revealed significant differences between macroinvertebrate gut and environmental microbiomes for all sites demonstrating that the bacterial community composition among microbiomes (macroinvertebrates, sediment, and water) was distinct. Macroinvertebrates also hosted greater numbers of antibiotic resistance genes (tetW, sulII, sulII) at most sites suggesting that macroinvertebrates are hotspots for ARGs. To explore the relationship between the presence of certain bacterial taxa and occurrence of specific ARGs, we examined the correlation between bacterial community composition and the ARG profile at the bacterial family level. Our findings indicated that certain bacterial taxa are tightly coupled with the ARGs examined. ARG abundance was also correlated with physicochemical conditions. For example, ammonium concentration was significantly correlated with sulII abundance, pH was significantly correlated with tetW abundance while sulI had no significant relationship with any of the physicochemical parameters. Overall, the differences in bacterial community composition along the urban gradient of Tinkers Creek appeared to be driven by environmental conditions and, in turn, are related to functional gene abundance.
