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Appl. Environ. Microbiol., Apr 1995, 1563-1570, Vol 61, No. 4
P Roslev and GM King
The capacity for anaerobic metabolism of endogenous and selected exogenous
substrates in carbon- and energy-starved methanotrophic bacteria was
examined. The methanotrophic isolate strain WP 12 survived extended
starvation under anoxic conditions while metabolizing 10-fold less
endogenous substrate than did parallel cultures starved under oxic
conditions. During aerobic starvation, the cell biomass decreased by 25%
and protein and lipids were the preferred endogenous substrates. Aerobic
protein degradation (24% of total protein) took place almost exclusively
during the initial 24 h of starvation. Metabolized carbon was recovered
mainly as CO(inf2) during aerobic starvation. In contrast, cell biomass
decreased by only 2.4% during anaerobic starvation, and metabolized carbon
was recovered mainly as organic solutes in the starvation medium. During
anaerobic starvation, only the concentration of intracellular
low-molecular-weight compounds decreased, whereas no significant changes
were measured for cellular protein, lipids, polysaccharides, and nucleic
acids. Strain WP 12 was also capable of a limited anaerobic glucose
metabolism in the absence of added electron acceptors. Small amounts of
CO(inf2) and organic acids, including acetate, were produced from exogenous
glucose under anoxic conditions. Addition of potential anaerobic electron
acceptors (fumarate, nitrate, nitrite, or sulfate) to starved cultures of
the methanotrophs Methylobacter albus BG8, Methylosinus trichosporium OB3b,
and strain WP 12 did not stimulate anaerobic survival. However, anaerobic
starvation of these bacteria generally resulted in better survival than did
aerobic starvation. The results suggest that methanotrophic bacteria can
enter a state of anaerobic dormancy accompanied by a severe attenuation of
endogenous metabolism. In this state, maintenance requirements are
presumably provided for by fermentation of certain endogenous substrates.
In addition, low-level catabolism of exogenous substrates may support
long-term anaerobic survival of some methanotrophic bacteria.
Copyright © 1995, American Society for Microbiology
Aerobic and Anaerobic Starvation Metabolism in Methanotrophic Bacteria
Department of Microbiology, Biochemistry, and Molecular Biology and Darling Marine Center, University of Maine, Walpole, Maine 04573
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