Extracellular Enzymatic Capabilities of Diverse Subsurface Marine Sediments (2016)

Undergraduates: Rachel Snider, Adrienne Hoarfrost

Faculty Advisor: Carol Arnosti
Department: Environmental Science

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Microbial communities in marine sediments play a crucial role in the cycling of organic carbon. However, measuring microbial hydrolytic activities in sediments is challenging due to high sorption rates of organic substrates to sediment particles. We developed a novel extraction treatment that facilitates recovery of added organic substrates, enabling direct measurement of heterotrophic activity in subsurface sediments. This extraction treatment was applied to sediments from diverse geochemical contexts from Guaymas Basin in the Gulf of California. Hydrolysis of two high-molecular-weight polysaccharides was measured at 5-10 cm and 55-60 cm sediment depth from six cores encompassing hemipelagic to hydrothermal conditions. Hydrolysis rates and capabilities varied greatly by both depth and sediment source, but activities were not highest in the cores from hydrothermally active sites, despite their high energy potential and organic carbon content. This suggests that there are other factors which affect the degradation of organic matter in Guaymas Basin, such as varying composition of organic carbon or differences in microbial community capacities to utilize specific organic substrates. The extraction treatment we developed was able to overcome sorption of organic substrates in order to directly measure extracellular enzymatic hydrolysis in a wide range of sediment types, enabling new insights into microbial carbon cycling and substrate preferences in the sediment environment.