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J. Bacteriol., Aug 1995, 4690-4695, Vol 177, No. 16
M Farwick, RM Siewe and R Kramer
Osmoregulatory uptake of glycine betaine in whole cells of Corynebacterium
glutamicum ATCC 13032 (wild type) was studied. The cells actively take up
glycine betaine when they are osmotically shocked. The total accumulation
and uptake rate were dependent on the osmotic strength of the medium.
Kinetic analysis revealed a high- affinity transport system (Km, 8.6 +/-
0.4 microM) with high maximum velocity (110 nmol.min-1.mg [dry weight]-1).
Glycine betaine functioned as a compatible solute when added to the medium
and allowed growth at an otherwise inhibitory osmotic strength of 1.5 M
NaCl. Proline and ectoine could also be used as osmoprotectants. Glycine
betaine is neither synthesized nor metabolized by C. glutamicum. The
glycine betaine transport system is constitutively expressed at a basal
level of activity. It can be induced up to eightfold by osmotic stress and
is strongly regulated at the level of activity. The transport system is
highly specific and has its pH optimum in the slightly alkaline range at
about pH 8. The uptake of the zwitterionic glycine betaine is mediated by a
secondary symport system coupled to cotransport of at least two Na+ ions.
It is thus driven both by the membrane potential and the Na+ gradient. An
extremely high accumulation (internal/external) ratio of up to 4 x 10(6)
was measured, which represents the highest accumulation ratio observed for
any transport system.
Copyright © 1995, American Society for Microbiology
Glycine betaine uptake after hyperosmotic shift in Corynebacterium glutamicum
Institut fur Biotechnologie 1, Forschungszentrum Julich, GmbH, Federal Republic of Germany.
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