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Applied and Environmental Microbiology, June 2000, p. 2358-2364, Vol. 66, No. 6
Equipe Osmoadaptation chez les
Bactéries, UMR CNRS 6026, Université de Rennes 1, Campus de Beaulieu, F-35042, Rennes, France
Received 15 December 1999/Accepted 3 April 2000
DL-Pipecolic acid (DL-PIP) promotes growth
restoration of Sinorhizobium meliloti cells facing
inhibitory hyperosmolarity. Surprisingly, D and
L isomers of this imino acid supplied separately were not
effective. The uptake of L-PIP was significantly favored in
the presence of the D isomer and by a hyperosmotic stress. Chromatographic analysis of the intracellular solutes showed that stressed cells did not accumulate radiolabeled L-PIP.
Rather, it participates in the synthesis of the main endogenous
osmolytes (glutamate and the dipeptide
N-acetylglutaminylglutamine amide) during the lag phase,
thus providing a means for the stressed cells to recover the osmotic
balance. 13C nuclear magnetic resonance analysis was used
to determine the fate of D-PIP taken into the cells. In the
absence of L-PIP, the imported D isomer was
readily degraded. Supplied together with its L isomer,
D-PIP was accumulated temporarily and thus might contribute
together with the endogenous osmolytes to enhance the internal osmotic
strength. Furthermore, it started to disappear from the cytosol when
the L isomer was no longer available in the culture medium
(during the late exponential phase of growth). Together, these results
show an uncommon mechanism of protection of osmotically stressed cells
of S. meliloti. It was proved, for the first time, that the
presence of the two isomers of the same molecule is necessary for it to
manifest an osmoprotective activity. Indeed, D-PIP seems to
play a major role in cellular osmoadaptation through both its own
accumulation and improvement of the utilization of the L
isomer as an immediate precursor of endogenous osmolytes.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Osmoprotection by Pipecolic Acid in
Sinorhizobium meliloti: Specific Effects of D
and L Isomers
*
Corresponding author. Mailing address: Equipe
Osmoadaptation chez les Bactéries, UMR CNRS 6026, Université de Rennes 1, Bâtiment 14, Campus de Beaulieu,
F-35042 Rennes, France. Phone and fax: 33 (0)2 99 28 61 40. E-mail:
tbernard{at}univ-rennes1.fr.
Applied and Environmental Microbiology, June 2000, p. 2358-2364, Vol. 66, No. 6
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
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