PhD Dissertation Defense: John Paul Balmonte

The PhD Dissertation Defense of John Paul “JP” Balmonte will be presented by the Department of Marine Sciences in seminar room G201 on the ground floor of Murray Hall, UNC at Chapel Hill and live broadcast to UNC IMS (Institute of Marine Science) seminar room 222 in Morehead City – NC. This event will be held on Monday, November 6th at 12:20 PM.

Title:  Microbial community composition, extracellular enzymatic activities, and structure-function relationships in the central Arctic Ocean, a high-latitude fjord, and the North Atlantic Ocean

Abstract: Due to their abundance, diversity, and profound capabilities to transform and metabolize diverse compounds, microbial communities regulate biogeochemical cycles on micro-, regional, and global scales. The activities of microbial communities have implications for the flow of matter, energy sources of other organisms, and human health, among countless others. Yet, the composition, diversity, and ecological roles of microbes in parts of the global oceans—from the high latitudes to the deep water column—remain unknown. Drawing from microbiological, oceanographic, and ecological concepts, this dissertation explores several fundamental topics: 1) the manner in which hydrographic conditions influence microbial community composition; 2) the ability of these microbial communities to break down organic compounds across environmental and depth gradients; and 3) microbial structure-function relationships in various habitats and under altered environmental regimes. In the central Arctic Ocean, the composition and enzymatic function of pelagic, particle associated and benthic bacterial communities varied with depth and region, largely due to specific hydrographic features. Structure-function relationships across habitats signified varying potentials for shifts in microbial community composition and breakdown of organic matter in the water column and sediments of the rapidly-changing Arctic Ocean. In Tyrolerfjord-Young Sound, northeast Greenland, microbial enzymatic activity patterns were investigated in rivers and within the fjord. Activity patterns correlated with the composition of bacterial communities and dissolved organic matter in the same waters, suggesting that factors extrinsic (organic matter supply) and intrinsic (composition) to microbial communities may concertedly influence their heterotrophic activities. Finally, functional consequences of differences in community composition were further explored in the North Atlantic. Enriched with high molecular weight organic matter, compositionally-distinct microbial communities exhibited convergent and divergent successional patterns. While convergent features were driven by several initially rare taxa, overarching successional differences in microbial community composition and enzymatic profiles provide evidence for the functional significance of community structure. The integration of community compositional analyses and empirical activity measurements has provided valuable information on the identity, ecological roles, and environmental sensitivity of microbial communities in previously unexplored oceanic regions and depths. These insights can be used to evaluate the potential for environmental changes to alter marine microbial community structure and function.