Functional variation among polysaccharide-hydrolyzing microbial communities in the Gulf of Mexico

Marine polysaccharides are structurally diverse, as are the microbial communities capable of remineralizing them. Variations in the diversity, richness, and metagenome content of pelagic microbial communities are well documented, but variation in the spectrum of substrates accessible to those communities is less well understood. Here we investigate variability in the abilities of microbial communities to access specific polysaccharides along lateral and depth gradients in the Gulf of Mexico. Patterns of polysaccharide degradation during long-term incubations varied in ways that could not be predicted from bulk community measurements of bacterial production and glucose metabolism. There was greater diversity of function among epipelagic communities than among mesopelagic communities, and the communities in the two deepest water samples (700 m and 905 m) were more specialized in their abilities to access specific polysaccharide structures than were shallower-water communities. Timecourses of polysaccharide hydrolysis suggest that the capacity of communities to access specific polysaccharides may be influenced in part by variability in the composition or activity of the rare biosphere.

► Pelagic microbial communities vary in their ability to access specific polysaccharides.
► Community function is variable in surface water, more homogenous below 125 m depth.
► Timecourses suggest possible role for rare biosphere in some samples.