Affiliation:
1. U.S. Geological Survey, 345 Middlefield Road, Menlo Park, California 94025, and Department of Biology and Microbiology, University of Wisconsin, La Crosse, Wisconsin 546012
Abstract
Demethylation of monomethylmercury in freshwater and estuarine sediments and in bacterial cultures was investigated with
14
CH
3
HgI. Under anaerobiosis, results with inhibitors indicated partial involvement of both sulfate reducers and methanogens, the former dominating estuarine sediments, while both were active in freshwaters. Aerobes were the most significant demethylators in estuarine sediments, but were unimportant in freshwater sediments. Products of anaerobic demethylation were mainly
14
CO
2
as well as lesser amounts of
14
CH
4
. Acetogenic activity resulted in fixation of some
14
CO
2
produced from
14
CH
3
HgI into acetate. Aerobic demethylation in estuarine sediments produced only
14
CH
4
, while aerobic demethylation in freshwater sediments produced small amounts of both
14
CH
4
and
14
CO
2
. Two species of
Desulfovibrio
produced only traces of
14
CH
4
from
14
CH
3
HgI, while a culture of a methylotrophic methanogen formed traces of
14
CO
2
and
14
CH
4
when grown on trimethylamine in the presence of the
14
CH
3
HgI. These results indicate that both aerobes and anaerobes demethylate mercury in sediments, but that either group may dominate in a particular sediment type. Aerobic demethylation in the estuarine sediments appeared to proceed by the previously characterized organomercurial-lyase pathway, because methane was the sole product. However, aerobic demethylation in freshwater sediments as well as anaerobic demethylation in all sediments studied produced primarily carbon dioxide. This indicates the presence of an oxidative pathway, possibly one in which methylmercury serves as an analog of one-carbon substrates.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
236 articles.
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