Affiliation:
1. Departments of Microbiology1 and
2. Chemical Engineering,2 University of Washington, Seattle, Washington 98195
Abstract
ABSTRACT
Some methane-oxidizing bacteria (methanotrophs) are known to be capable of expressing nitrogenase and utilizing N
2
as a nitrogen source. However, no sequences are available for
nif
genes in these strains, and the known nitrogen-fixing methanotrophs are confined mainly to a few genera. The purpose of this work was to assess the nitrogen-fixing capabilities of a variety of methanotroph strains.
nifH
gene fragments from four type I methanotrophs and seven type II methanotrophs were PCR amplified and sequenced. Nitrogenase activity was confirmed in selected type I and type II strains by acetylene reduction. Activities ranged from 0.4 to 3.3 nmol/min/mg of protein. Sequence analysis shows that the
nifH
sequences from the type I and type II strains cluster with
nifH
sequences from other gamma proteobacteria and alpha proteobacteria, respectively. The translated
nifH
sequences from three
Methylomonas
strains show high identity (95 to 99%) to several published translated environmental
nifH
sequences PCR amplified from rice roots and a freshwater lake. The translated
nifH
sequences from the type II strains show high identity (94 to 99%) to published translated
nifH
sequences from a variety of environments, including rice roots, a freshwater lake, an oligotrophic ocean, and forest soil. These results provide evidence for nitrogen fixation in a broad range of methanotrophs and suggest that nitrogen-fixing methanotrophs may be widespread and important in the nitrogen cycling of many environments.
Publisher
American Society for Microbiology
Subject
Ecology,Applied Microbiology and Biotechnology,Food Science,Biotechnology
Cited by
156 articles.
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