Grantee Research Project Results

Controls on the Activity of Microbial Extracellular Enzymes in Estuarine and Coastal Waters.

EPA Grant Number: F6E21109
Title: Controls on the Activity of Microbial Extracellular Enzymes in Estuarine and Coastal Waters.
Investigators: Steen, Andrew D
Institution: University of North Carolina at Chapel Hill
EPA Project Officer: Packard, Benjamin H
Project Period: September 1, 2006 through September 1, 2009
Project Amount: $101,212
RFA: STAR Graduate Fellowships (2006) RFA Text |  Recipients Lists
Research Category: Academic Fellowships , Fellowship - Aquatic Ecology and Ecosystems , Fellowship - Chemical Oceanography

Objective:

Heterotrophic bacteria act as ‘recyclers’ in aquatic ecosystems by consuming detrital organic matter and transforming it into biomass or respiring it into CO2. Bacteria rely on extracellular enzymes to hydrolyze high molecular weight organic matter (HMW OM) prior to uptake. Hydrolysis by extracellular enzymes therefore represents a potential bottleneck in the microbial degradation of organic matter. The goal of this project is to constrain the factors that influence production and degradation of extracellular enzymes in pelagic environments. This will be addressed via three research questions: 1.) What factors influence production of specific extracellular enzymes in environments in which they are inactive? 2.) What factors are most important in degrading extracellular enzymes in pelagic marine environments? 3.) What are the half lives of extracellular enzymes in those environments?

Approach:

Question 1) I will treat water samples with substances which might influence microbial growth, activity, or induction or repression of extracellular enzymes. I then monitor extracellular enzyme activity, microbial community density, and community composition. These data will allow me to determine whether extracellular enzyme activity was regulated by classical induction/repression mechanisms, by presence of labile carbon or nitrogen substrates, or by composition of the microbial community.
Question 2) Factors including photochemical interactions, humic substances, presence of surfaces and protease activity might affect extracellular enzyme half lives. I will manipulate these factors at realistic, environmental levels in model systems (for instance artificial seawater spiked with commercial enzymes) and measure enzyme half lives in order to determine what is most likely important in controlling enzyme half lives in pelagic marine environments.
Question 3) The duration of enzyme half-lives in the ocean is almost entirely unknown. I will measure half-lives of cell-free enzymes by determining the rate at which enzyme activity decays in 0.2 µm-filtered seawater across an environmental gradient (for instance, a salinity transect of an estuary). The patterns observed will help explain the ‘costs’ in energy and nutrients required for enzymes to produce extracellular enzymes.

Expected Results:

The combined results from the above experiments will help explain why patterns of extracellular enzyme activity have been observed to vary widely even between apparently similar environments, and will help to constrain the true ‘costs’ and ‘benefits’ (in terms of carbon, nutrients, and energy) of enzyme production by heterotrophic bacteria.

Supplemental Keywords:

Heterotrophic microbes, extracellular enzymes, carbon cycle, dissolved organic carbon,, RFA, Scientific Discipline, Ecosystem Protection/Environmental Exposure & Risk, Aquatic Ecosystems & Estuarine Research, Oceanography, Aquatic Ecosystem, Environmental Monitoring, Ecology and Ecosystems, coastal ecosystem, dissolved organic matter, estuarine research, marine organisms, microbial degradation, bacterial biomass, biomass

Progress and Final Reports:

2007

2008

Final