Increase in osmotolerance of Rhizobium fredii soybean isolate BD32 by the proB proA operon of Escherichia coli

The proB proA operons (which are blocked by the feedback inhibition of proline production) of Escherichia coli wild type or with tile mutation proB(osm), blocking feedback inhibition effect of proline production, were cloned in a broad host range shuttle vector pVA 12-2. The hybrid plasmids pLVA(proB(+)A(+)) and pNSA(proB(osm) proA) were transferred into a low level osmotolerance Rhizobium fredii strain BD32. Both types of transconjugants were characterised by increased osmotolerance in a minimal medium supplied with 0.4-0.8 M NaCl but in the case of pNSA the effect was more significant. The strain BD32/pNSA had all increased level of intracellular proline concentration. Practical application of the increase in Rhizobium resistance to the stress factors is discussed. (C) 1995 Academic Press, Inc.