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Appl. Environ. Microbiol., Jun 1997, 2252-2257, Vol 63, No. 6
LM Proctor, R Lai and RP Gunsalus
Methanogenic Archaea are found in a wide range of environments and use
several strategies to adjust to changes in extracellular solute
concentrations. One methanogenic archaeon, Methanosarcina thermophila TM-1,
can adapt to various osmotic conditions by synthesis of alpha- glutamate
and a newly discovered compatible solute, Ne-acetyl-beta- lysine, or by
accumulation of glycine betaine (betaine) and potassium ions from the
environment. Since betaine transport has not been characterized for any of
the methanogenic Archaea, we examined the uptake of this solute by M.
thermophila TM-1. When cells were grown in mineral salts media containing
from 0.1 to 0.8 M NaC1, M. thermophila accumulated betaine in
concentrations up to 140 times those of a concentration gradient within 10
min of exposure to the solute. The betaine uptake system consisted of a
single, high-affinity transporter with an apparent K3 of 10 microM and an
apparent maximum transport velocity of 1.15 nmol/min/mg of protein. The
transporter appeared to be specific for betaine, since potential
substrates, including glycine, sarcosine, dimethyl glycine, choline, and
proline, did not significantly inhibit betaine uptake. M. thermophila TM-1
cells can also regulate the capacity for betaine accumulation, since the
rate of betaine transport was reduced in cells pregrown in a
high-osmolarity medium when 500 microM betaine was present. Betaine
transport appears to be H+ and/or Na+ driven, since betaine transport was
inhibited by several types of protonophores and sodium ionophores.
Copyright © 1997, American Society for Microbiology
The methanogenic archaeon Methanosarcina thermophila TM-1 possesses a high-affinity glycine betaine transporter involved in osmotic adaptation
Department of Microbiology and Molecular Genetics, University of California at Los Angeles 90095-1489, USA.
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