Transient accumulation of glycine betaine and dynamics of endogenous osmolytes in salt-stressed cultures of Sinorhizobium meliloti

• Published in: Applied and Environmental Microbiology 1997-12, Vol.63 (12), p.4657-4663
• Main Authors: Talibart, R, Jebbar, M, Gouffi, K, Pichereau, V, Gouesbet, G, Blanco, C, Bernard, T, Pocard, J.A
• Format: Article
• Language: English
• Subjects: Action of physical and chemical agents on bacteria; Bacteriology; Biochemistry; Biochemistry, Molecular Biology; Biodiversity and Ecology; Biological and medical sciences; Biology of microorganisms of confirmed or potential industrial interest; Biotechnology; CHLORURE DE SODIUM; CLORURO SODICO; Ecology, environment; Ecosystems; Ecotoxicology; Environmental Sciences; Fundamental and applied biological sciences. Psychology; Genomics; Global Changes; Life Sciences; Microbiology; Mission oriented research; Molecular biology; Osmosis; Physiology and metabolism; RHIZOBIUM; SALINIDAD; SALINITE; SALINITY; SODIUM CHLORIDE; Toxicology; Vegetal Biology
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/aem.63.12.4657-4663.1997

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 13C 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 step, 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