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 the mutation proBosm, 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(proBosm 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 an increased level of intracellular proline concentration. Practical application of the increase in Rhizobium resistance to the stress factors is discussed.