Grantee Research Project Results

Final Report: The Effect of Atrazine on Dimethyl Sulfur in Marine Phytoplankton

EPA Grant Number: F07E71122
Title: The Effect of Atrazine on Dimethyl Sulfur in Marine Phytoplankton
Investigators: Spiese, Christopher E.
Institution: The State University of New York
EPA Project Officer: Hahn, Intaek
Project Period: September 1, 2007 through September 1, 2010
RFA: Minority Academic Institutions (MAI) Fellowships for Graduate Environmental Study (2003) RFA Text |  Recipients Lists
Research Category: Fellowship - Oceanography , Fellowship - Aquatic Ecology and Ecosystems , Academic Fellowships

Objective:

Dimethyl sulfide (DMS) is thought to play a key role in climate regulation, as its oxidation leads to the formation of cloud condensation nuclei in the atmosphere. Although DMS is produced by marine phytoplankton from dimethylsulfoniopropionate (DMSP), its role in the cell is poorly understood. This study aims to look at DMS and its potential as an antioxidant compound – one that prevents damage caused by free radicals in the cell. It examined this role through fundamental studies related to the processes leading to the production and loss of DMS in the cell, as well as stress studies to assess how the concentration of each species as well as the various processes change in response to this stress.

Rationale:

This project focused on laboratory cultures of axenic marine algae. Three classes of marine algae were tested: diatoms, prymnesiophytes, and dinoflagellates. In the first part, a broad spectrum of algal species were examined for their ability to reduce DMSO to DMS in vitro with additional bioinformatics studies looking for a potential enzymatic function that may explain the observed activity. Photochemical studies examining the production of DMS and DMSO, as well as other oxidized sulfur species, were conducted to assess the capability of algae to produce DMS(O) in response to external, nonchemical stresses. Finally, a novel model of DMS concentrations in marine algae was put forth to constrain the concentration and thereby the function of this compound in vivo. Atrazine and nutrient stress experiments were conducted to tie together the various processes and species operating on DMS in the cell.

Conclusions:

DMS was found to be produced from the reduction of DMSO in all marine phytoplankton tested. The putative enzyme responsible, MsrA, is a repair enzyme for methionine sulfoxide residues in protein. Reactive oxygen species such as superoxide and the OH radical were found to react with DMSP to produce DMS and DMSO, which suggests that the production of these compounds under stress conditions is not limited to species that express an active DMSP lyase activity. Finally, given the various processes that produce and consume DMS in vivo, the concentration of this compound is expected to be significantly less than was previously believed. Instead of 1-60 mM, it may actually lie in the range of 2-40 nM. This indicates that DMS likely will not be an effective antioxidant in vivo. In support of these results, atrazine and nitrogen stress experiments suggest that DMSP and DMSO concentrations will be significantly elevated during stress, as well as the DMSO reduction activity. This strongly suggests that DMS production and possibly DMS concentrations will likewise be elevated in response to stress.

Supplemental Keywords:

Atrazine, dimethylsulfide, dimethylsulfoniopropionate, dimethylsulfoxide, marine algae, reactive oxygen species, antioxidant,

Progress and Final Reports:

Original Abstract

2008

2009