Throughout the world’s oceans, bacteria are constantly working to degrade organic matter generated by phytoplankton and other organisms. To do this, they use enzymes to convert detritus into smaller and more “available” forms, i.e., usable food that can be further digested by other members of the microbial community. This critical link in the ocean’s carbon cycle seems like a straightforward function, but it’s much more complex than a few types of bacteria acting as the ocean’s food processing plant. For example, sometimes no one in the bacterial community has the right type of enzyme needed to chop up (hydrolyze) a particular type of detritus; other times “selfish” bacteria consume everything they hydrolyze instead of providing food for other bacteria.
To explore these bacterial functions and better understand larger-scale carbon cycling, researchers from UNC Marine Sciences and the Max Planck Institute for Marine Microbiology (Bremen, Germany) will be sailing on the North Atlantic this May aboard the R/V Endeavor, collecting water samples and carrying out experiments to study microbial processing of organic matter. Dr. Carol Arnosti will be the chief scientist on the cruise, which will target several areas in the northwest Atlantic, targeting the Gulf Stream, the Labrador current, and the Sargasso Sea. Scientists will collect water samples from multiple depths from the surface to bottom waters (ca. 5000 m), and analyze differences in microbial community structure and enzyme activities, as well as the concentration and structure of the organic matter that serves as bacterial food. These properties are expected to vary across water masses and depths.
Doctoral students Chad Lloyd (UNC Marine Sciences) and Sarah Brown (UNC Environment, Ecology and Energy Program) will be instrumental in conducting incubation experiments to determine enzyme use. To do this, they’ll be introducing a variety of substrates, e.g., simple sugars, complex polysaccharides, peptides, and phytoplankton-derived organic matter, to the water samples collected at sea, and then determining how the community composition changes—and whether or not bacteria have a preferred substrate. Brown has participated in multiple research cruises, including one to the Indian and Southern Oceans, and this will be her second cruise in the North Atlantic. This will be Lloyd’s first cruise, and an opportunity to collect a compelling dataset for dissertation work. When asked about the most exciting part of the cruise? “The food – especially the ice cream.” Scientists have favorite substrates, too.
The cruise, funded by the Chemical Oceanography program of the National Science Foundation, will last for sixteen days in late May; check back in June for photos and stories from the field!