Rivers receive continuous influx of organic carbon from their watersheds. The breakdown of organic carbon, particularly plant biomass, depends on the activity of microbial carbohydrate-active enzymes (CAZymes). Rivers are also extremely dynamic environments with continuous sediment turnover, highly variable local inputs, and an influx of microbes from the watershed with high functional diversity. The upper region of sediment is particularly prone to rapid turnover and instability. These processes could significantly affect CAZyme diversity and abundance, and therefore impact ecosystem carbon flow. However, little is currently known about the drivers of microbial functional diversity in lotic environments. The Kanawha-New River basin includes a watershed in the Appalachian Mountains of about 12,000 square miles with a variety of local inputs such as waste treatment effluent and surface mining. We sampled the sediment microbiome from three widely-spaced locations along an 80 km section of the Kanawha River (WV). One location was in the heart of an eighty-year chemical industry and two sites were in forested regions far upstream. Our long-term research seeks to understand the impact of land-use practices on watershed microbial ecosystem processes across scales. For this study, we tested the diversity and distribution of CAZymes in river sediment. We collected replicate sediment samples from 0-5 and 5-10 cm layers of sediment using an 8 cm diameter corer. Total DNA was extracted and 4.8 to 14.2 million paired-end reads were obtained per sample using Illumina HiSeq. Metagenome analysis was done using FragGeneScan. Carbohydrate-active enzyme diversity was identified using dbCAN and the CAZy database. Organic carbon was measured with an Aurora Total Organic Carbon Analyzer.
Results/Conclusions
CAZymes were predominantly found in six major classes: glycoside hydrolases (GH), polysaccharide lyases, carbohydrate esterases, glycosyl transferases (GT), carbohydrate-binding modules, and auxiliary activities. The total number of CAZyme families per sample ranged from 82 to 100. Total organic carbon varied about 5-fold among samples. In contrast to previous studies of soils where GHs were most abundant, the GTs were the most abundant class (58-64%) in every sediment sample. The second most abundant class was GHs (20-22%). GTs are used for biosynthesis of complex carbohydrates such as cellulose, chitin and others. In conclusion, the diversity of sediment CAZymes was quite similar in all locations even those impacted by heavy industry or widely separated, indicating that local environmental factors have minimal effects on CAZyme diversity. Acknowledgements: Funding was provided by NSF Appalachian Freshwater Initiative grant #OIA-1458952.