Masters Theses

Date of Award

8-2017

Degree Type

Thesis

Degree Name

Master of Science

Major

Geology

Major Professor

Andrew Steen

Committee Members

Ed Perfect, Mike Mckinney

Abstract

A longstanding goal of organic biogeochemistry is to open the “black box” of microbial community metabolic capacity in order to understand how the vast complexity of organic chemical structures and microbial metabolisms give rise to observed patterns of organic matter reactivity. Microbial communities use diverse suites of extracellular enzymes to access complex organic compounds, which constitute the majority of bioavailable organic matter. Peptidase enzymes are responsible for degradation of protein, there are both endopeptidase and exopeptidase enzymes which cleave proteins from the end or the middle, respectively. Other than the exopeptidase enzyme Leucyl Aminopeptidase, constraints on peptidase activity are unknown. The purpose of this research is to determine what, if any, environmental variables control the production peptidase enzymes. Here we investigate the extent to which the freshness of organic matter and other water quality parameters control pathways of protein degradation as indicated by the ratio of exopeptidases to endopeptidases. Potential endo- and exopeptidase activities were measured in 32 freshwater samples from eastern TN and northeastern PA. We compared enzyme activities to organic matter concentrations and character, cell abundance, nutrient concentrations, and environmental parameters. There is evidence indicating that the ratio of endo- to exopeptidase activities are influenced by dissolved organic carbon (DOC) concentration and freshness. There is a similar relationship between endopeptidase to exopeptidase activity and cell densities, despite there being no correlation between DOC concentration and cell density. Fluorescent dissolved organic matter (FDOM) data indicates that terrestrial DOC dominates systems when DOC > 275 μmol [micromoles] L-1 (per liter) whereas DOC < 275 μmol [micromoles] L-1 there is a mixture of carbon derived from microorganisms and terrestrial sources. These results indicate that the metabolic capacities of freshwater microbial communities influence the reactivity of specific classes of molecules within the protein-like fraction of dissolved organic matter (DOM) and are the characteristics of organic matter. Additionally, relationships exist between the ratio of endopeptidase to exopeptidase activity and temperature, pH, dissolved oxygen, and cell abundance. Despite the influence organic carbon (OC) freshness and cell density have on the production of endopeptidases and exopeptidases this is a very dynamic system which is influenced by several environmental factors.

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