Microbial degradation of organic macromolecules in Arctic fjords and in the Gulf of Mexico

• Main Author: Steen, Andrew D.
• Other Authors: College of Arts and Sciences, Department of Marine Sciences, Arnosti, Carol
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: University of North Carolina at Chapel Hill 2009
• Subjects: Arctic; Arctic Ocean; Svalbard
• Online Access: https://doi.org/10.17615/3zys-5043; https://cdr.lib.unc.edu/downloads/jw827b894?file=thumbnail; https://cdr.lib.unc.edu/downloads/jw827b894

Polysaccharides represent a labile, abundant class of marine dissolved organic matter (DOM), which must be hydrolyzed by extracellular enzymes prior to uptake by heterotrophic microbes. Pelagic microbial communities differ in their ability to access polysaccharides: some communities are completely incapable of accessing certain polysaccharides which are readily hydrolyzed elsewhere. I measured enzymatic hydrolysis of structurally defined polysaccharides in the Gulf of Mexico and in Svalbard fjords (Arctic Ocean), and investigated the factors that influenced enzyme activities. Arctic communities were able to access a narrower range of polysaccharide structures than Gulf of Mexico surface water communities, but Gulf of Mexico mesopelagic (>100 m depth) communities also accessed a limited range of polysaccharides. Attempts to induce expression of pullulanase, which was not present in Arctic samples, suggested that the Arctic communities were totally incapable of expressing pullulanase, most likely for lack of the necessary genes. Half-lives of extracellular enzymes in seawater were on the order of tens to hundreds of hours, long enough for extracellular enzymes to become decoupled from the microbes that produced them. These results point to functional differences in DOM processing among marine microbial communities, indicating that DOM lability is a function of the microbial community present as well as DOM chemical characteristics.