Microbial niche differentiation in enzymatic activities shaped by particle-association and salinity differences in a high latitude fjord (2016)

Undergraduates: Karylle Abella, John Paul Balmonte

Faculty Advisor: Carol Arnosti
Department: Chemistry

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Glacial meltwater exports significant amounts of organic carbon and nutrients to fjords, fueling microbial heterotrophy and primary productivity. High organic carbon burial rates in fjords, however, imply that some glacial and autochthonous organic carbon evade complete remineralization in surface waters, and sink to the bottom of fjords. Hence, microbially-mediated organic carbon transformations determine the quantity and quality of carbon sources available to deep life. To investigate the manner in which fresh glacial meltwater influence microbial carbon processing in a high latitude fjord, we compare whole community versus particle-associated freshwater and marine microbial enzymatic activities from glacial-fed rivers, which connect to the Tyrolerfjord-Young Sound system in northeast Greenland. Using diverse peptide substrates, we measured lowest enzymatic activities by freshwater microbes, and highest by their marine counterparts. In addition, the spectrum of hydrolyzed substrates differ along a salinity gradient, but do not vary between surface and subsurface waters at the same site. Differences between whole-community versus particle-associated enzymatic activities indicate varying enzymatic strategies of particle-associated versus free-living heterotrophic microbes. Altogether, these results demonstrate an apparent microbial niche differentiation in carbon processing associated with salinity differences and particle-association in fjords affected by glacial meltwater.