ProB gene from the wild-type strain of Bacillus subtilis 93151 and proA gene from the salt tolerant mutant of Bacillus subtilis 93151-14 were amplified using PCR method respectively.PCR products were ligated into the both sides of the linear plasmid pBE2 digested by using pstⅠ and SacⅠ.The ligation mixtures were transformed into proline auxotrophic strain Escherichia coli JM83 for in vivo recombination.The transformant harboring the recombination vector containing the wild-type proB gene and the mutated proA hybrid gene were selected by functional complementation of E.coli JM83.The salt-tolerance of three transformants（containing the hybrid proBA gene

the wild type proBA gene and the mutated proBA gene

respectivly） was examined.The salt-tolerance of transformant containing the hybrid proBA gene（0.45 mol/L） is higher than that of transformant containing the wild type proBA gene（0.3 mol/L）

although the salt-tolerance of it is lower than that of transformant containing the mutated proBA gene（0.5 mol/L）.Intracellular free proline levels of three E.coli JM83 transformants increased in response to the elevated salt concentration.It is suggested that the accumulation of intracellular free proline play a particularly important role in improving the osmotolerance stress of E.coli transformant.In the same salt concentration

intracellular free proline level of transformant containing the hybrid proBA gene was lower than that of transformant carrying the mutated of proBA gene

but it is higher than that of transformant containing wild-type proBA genes obviously.The contribution of the mutation of proA gene could not be neglected in the improvement of the osmotic stress tolerance

although the mutation of proB gene was a key factor in improving osmotic stress tolerance.