Selective processing of organic matter by microbial communities in the Tar and Neuse Rivers (2011)

Undergraduates: Kimberly deLong, Avery Bullock, Shannon Smith, Ben Rhodes Sherif Ghobrial, Kai Ziervogel

Faculty Advisor: Carol Arnosti
Department: Geology

---

Heterotrophic bacteria are responsible for the degradation of dissolved and particulate organic matter in riverine systems. In order to access high molecular weight compounds, bacteria must produce extracellular enzymes that hydrolyze substrates outside of the cell to sizes sufficiently small for uptake. Although the importance of these processes and their implication for nutrient cycling is recognized, little information is available about the substrate specificity and activity of the diverse suite of enzymes produced by heterotrophic microbial communities. As part of an integrated investigation of microbial community composition and activities, we used high molecular weight substrates to determine the substrate specificities and activities of extracellular enzymes active in the degradation of polysaccharides. As substrates, we used fluorescently labeled laminarin, pullulan, arabinogalactan, fucoidan, xylan, and chondroitin sulfate. These soluble polysaccharides represent a diverse range of aquatic and terrestrial sources. Our objective was to compare the enzymatic response of the microbial community in the water column from both upstream and downstream locations in the Neuse and Tar Rivers, across a span of six months. The varied activities of these enzymes implies that the abilities of heterotrophic microbial communities to access high molecular weight substrates varies by season and location, and provides clues as to which substrates the microbial communities use.