Osmoprotection mechanisms in rhizobia isolated from Vicia faba var. major and Cicer arietinum

Research of mechanisms involved in osmoprotection of two rhizobia strains i solated from nodules of Vicia faba var. major and one strain nodulating Cic er arietinum, showed that choline and glycine-betaine improved growth in sa lt stress conditions. Provided radioactive choline was converted into glyci ne betaine catabolized at low osmolarity and accumulated under osmotic stre ss. Enzyme activities involved in the synthesis of glycine betaine from cho line were not modified by salt whereas addition of choline to the growth me dium enhanced them. Exogenous radioactive glycine betaine was accumulated i n salt stressed bacteria after one hour incubation but catabolized four hou rs later, suggesting a transient accumulation. Growth experiments indicated that betaine and its derivatives could be used as nitrogen and carbon sour ces. An investigation, by liquid phase chromatography, revealated accumulat ion of glutamate and alanine at different levels according to the strain an d degree of stress.