Microbiol. Rev., Jun 1996, 439-471, Vol 60, No. 2
RS Hanson and TE Hanson
Methane-utilizing bacteria (methanotrophs) are a diverse group of gram-
negative bacteria that are related to other members of the Proteobacteria.
These bacteria are classified into three groups based on the pathways used
for assimilation of formaldehyde, the major source of cell carbon, and
other physiological and morphological features. The type I and type X
methanotrophs are found within the gamma subdivision of the Proteobacteria
and employ the ribulose monophosphate pathway for formaldehyde
assimilation, whereas type II methanotrophs, which employ the serine
pathway for formaldehyde assimilation, form a coherent cluster within the
beta subdivision of the Proteobacteria. Methanotrophic bacteria are
ubiquitous. The growth of type II bacteria appears to be favored in
environments that contain relatively high levels of methane, low levels of
dissolved oxygen, and limiting concentrations of combined nitrogen and/or
copper. Type I methanotrophs appear to be dominant in environments in which
methane is limiting and combined nitrogen and copper levels are relatively
high. These bacteria serve as biofilters for the oxidation of methane
produced in anaerobic environments, and when oxygen is present in soils,
atmospheric methane is oxidized. Their activities in nature are greatly
influenced by agricultural practices and other human activities. Recent
evidence indicates that naturally occurring, uncultured methanotrophs
represent new genera. Methanotrophs that are capable of oxidizing methane
at atmospheric levels exhibit methane oxidation kinetics different from
those of methanotrophs available in pure cultures. A limited number of
methanotrophs have the genetic capacity to synthesize a soluble methane
monooxygenase which catalyzes the rapid oxidation of environmental
pollutants including trichloroethylene.
Copyright © 1996, American Society for Microbiology
Methanotrophic bacteria
Department of Microbiology, University of Minnesota, Minneapolis 55455, USA. hanso061@maroon.tc.umn.edu
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