CHOLINE AND GLYCINE BETAINE UPTAKE IN VARIOUS STRAINS OF RHIZOBIA ISOLATED FROM NODULES OF VICIA-FABA VAR MAJOR AND CICER-ARIETINUM L - MODULATION BY SALT, CHOLINE, AND GLYCINE BETAINE

Two strains of Rhizobia isolated from nodules of Vicia faba var. major and one strain isolated from nodules of Cicer arietinum L. were chara cterized for salt resistance. The presence of 1 mM glycine betaine or choline in a minimal medium with added NaCl had a beneficial role on t he growth of the three strains. Both molecules were found to be taken up by cells obtained at low osmolarity, and whereas glycine betaine up take activity was stimulated significantly in cells grown in the prese nce of 0.15 M NaCl, choline uptake activity was strongly inhibited by salt in all tested strains. However. in cells grown with exogenous cho line, the uptake inhibition exerted by salt was relieved, mainly in th e strain isolated from nodules of C. arietinum L. On the basis of kine tics determinations, in control cells as well as in salt-stressed cell s, only high-affinity activities were observed for glycine betaine and choline (apparent K(m)s between 3 and 18 mu M). Periplasmic proteins that bound glycine betaine or choline were identified. in nondenaturin g conditions, these proteins extracted from the various strains showed different electrophoretic mobility with always a less negative entire charge than the analogous proteins from Rhizobium meliloti.