LINKING THE ENZYMATIC REPERTOIRE OF HETEROTROPHIC BACTERIA TO COMMUNITY COMPOSITION, CARBOHYDRATE INVENTORIES, AND PHYSICAL OCEANOGRAPHY IN THE WESTERN NORTH ATLANTIC

Abstract

The balance of carbon between the atmosphere and ocean—which ultimately impacts the Earth’s climate—is dependent upon the production of organic matter by algae and its fate after being processed by heterotrophic microorganisms. In fact, heterotrophic bacteria—which can be particle-associated or free-living—are responsible for processing an estimated half of the organic matter that phytoplankton synthesize in the surface ocean. A large proportion of this organic matter is in the form of polysaccharides, or structurally complex, high molecular weight sugars. To transform this complex organic matter, microbes must produce enzymes of the correct structural specificity to transform it to smaller pieces that can be brought into the cell. The extent and rates to which bacteria can hydrolyze organic matter determines how much carbon is transformed for a given microbial community. Because microbial community composition differs with location and depth in the ocean, quantifying the enzymatic activities and complexity of organic matter at different stations and depths is essential to measuring patterns in microbial functional capabilities. Links between microbial community composition, their enzymatic function, and the structural complexity of the organic matter that they process are only beginning to be established. This dissertation focuses on characterizing the hydrolysis rates and substrate specificities of extracellular enzymes from three cruises in the western North Atlantic, leading to insights into the way the structural complexity of organic matter may be linked to differences in measured activities. We found that 1) bacteria on particles have an enhanced capability to degrade organic matter; 2) regional patterns of polysaccharide hydrolase activities could be driven by the physical oceanography of the region; and 3) the structural complexity of polysaccharides differed considerably by location, even though their monosaccharide building blocks were similar. The data and findings presented here highlight the extent to which microbial community composition and function, the structural complexity of organic matter, and the physical oceanography of the western North Atlantic are interwoven and contribute to the overall transformation of carbon in the ocean.Doctor of Philosoph