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Appl. Environ. Microbiol., Dec 1997, 4657-4663, Vol 63, No. 12
R Talibart, M Jebbar, K Gouffi, V Pichereau, G Gouesbet, C Blanco, T Bernard and J Pocard
The fate of exogenously supplied glycine betaine and the dynamics of
endogenous osmolytes were investigated throughout the growth cycle of
salt-stressed cultures of strains of Sinorhizobium meliloti which differ in
their ability to use glycine betaine as a growth substrate, but not as an
osmoprotectant. We present (sup13)C nuclear magnetic resonance spectral and
radiotracer evidence which demonstrates that glycine betaine is only
transiently accumulated as a cytoplasmic osmolyte in young cultures of
wild-type strains 102F34 and RCR2011. Specifically, these strains
accumulate glycine betaine as a preferred osmolyte which virtually prevents
the accumulation of endogenous osmolytes during the lag and early
exponential phases of growth. Then, betaine levels in stressed cells
decrease abruptly during the second half of the exponential phase. At this
stage, the levels of glutamate and the dipeptide
N-acetylglutaminylglutamine amide increase sharply so that the two
endogenous solutes supplant glycine betaine in the ageing culture, in which
it becomes a minor osmolyte because it is progressively catabolized.
Ultimately, glycine betaine disappears when stressed cells reach the
stationary phase. At this stage, wild-type strains of S. meliloti also
accumulate the disaccharide trehalose as a third major endogenous osmolyte.
By contrast, glycine betaine is always the dominant osmolyte and strongly
suppresses the buildup of endogenous osmolytes at all stages of the growth
cycle of a mutant strain, S. meliloti GMI766, which does not catabolize
this exogenous osmoprotectant under any growth conditions.
Copyright © 1997, American Society for Microbiology
Transient Accumulation of Glycine Betaine and Dynamics of Endogenous Osmolytes in Salt-Stressed Cultures of Sinorhizobium meliloti
Groupe Membranes et Osmoregulation, UPRES-A CNRS 6026, Universite de Rennes 1, Campus de Beaulieu, 35042 Rennes, France
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