Links between regional and depth patterns of microbial communities and enzyme activities in the western North Atlantic Ocean

Heterotrophic bacteria process much of the organic matter produced by phytoplankton in the ocean. A large proportion of this organic matter is in the form of polysaccharides, structurally complex, high molecular weight sugars. To consume this complex organic matter, microbes must initially produce enzymes of the correct structural specificity to transform it to smaller pieces that can be brought into the cell. The extent to which bacteria can hydrolyze organic matter determines how much carbon is transformed by a given microbial community. Because microbial community composition differs with location and depth in the ocean, quantifying their enzymatic potential at different stations and depths is essential to reveal patterns in microbial functional capabilities. To investigate links between patterns of bacterial composition and function, we assessed the bacterial community composition and measured glucosidase, peptidase, and polysaccharide hydrolase activities throughout the water column at 16 stations in the western North Atlantic. We found that bacterial community composition and polysaccharide hydrolase activities were depth stratified and showed regional variability, while glucosidase and peptidase activities were more similar among locations and depths. These findings suggest that polysaccharide hydrolase activities are expressed by a narrower range of organisms within bacterial communities, while the abilities to degrade peptides occurs more widely among community members, likely due to the broader substrate specificity for proteins compared to polysaccharides. The data and findings presented here highlight the extent to which patterns of microbial community composition and function and the physical oceanography of the western North Atlantic are interwoven and contribute to the overall transformation of carbon in the ocean.