Proposal Defense: C. Chad Llyod

The University of North Carolina at Chapel Hill Department of Marine Sciences presents the PhD Proposal Defense of graduate student, C. Chad Lloyd. The location of this event will be in seminar room G201 on the ground floor of Murray/Venable Hall on UNC-CH campus in Chapel Hill, NC. This event will be held on Wednesday, December 4th at 12:15 pm. This seminar will also be broadcast live to both UNC’s Institute of Marine Sciences room 222 and online via Zoom (Meeting ID: 919-962-0190).

Seminar Title: Investigating the role of heterotrophic bacteria in organic matter transformations throughout the biological pump

Abstract: Organic matter biosynthesized by phytoplankton in the euphotic zone is extensively cycled in the upper ocean. A small fraction of phytoplankton-derived organic matter reaches the deep ocean and contributes to deep sea sediments, removing CO2 from the atmosphere (the ‘biological pump’). The fate of sinking organic matter is dependent upon the activities of heterotrophic bacteria, which colonize and degrade these sinking particles as they pass through the mesopelagic zone. In the sediments, bacteria act as a ‘final filter’ that determine the extent to which organic matter is buried over geologic time. Microbes carry out the initial step in remineralization of complex organic matter by producing a diverse array of enzymes to hydrolyze complex substrates outside the cell to sizes that can be transformed and respired after transport into the cell. The fate of complex organic matter is therefore dependent on the specific enzymes produced by disparate bacterial communities at different depths and locations in the ocean. Currently, we lack knowledge on the specificity of extracellular enzymes associated with different bacterial communities present in distinct locations within the water column and sediments. In sediments, moreover, little information is available about intermediate processes between initial hydrolysis and terminal remineralization of organic carbon. My dissertation will first focus on mapping out rates and substrate specificities of extracellular enzyme activities from three cruises in the NW Atlantic, examining the extent to which particle-associated and free-living bacterial communities differ in composition and functional capabilities. In sediments, I will investigate a critical early transformation—the mobilization of dissolved organic matter (DOM) from particulate organic matter—and I will monitor changes quasi real-time in chemical characteristics of the DOM that is mobilized using microfluidic devices. These investigations of organic matter transformations in the water column and sediments will provide new insight into the capabilities and limitations of the microbial actors driving aspects of the biologic pump.