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[Isolation of a spontaneous mutant of Escherichia coli superproducing proline and resistant to elevated concentrations of NaCl].

We obtained a spontaneous mutant of Escherichia coli that was characterized by both proline superproduction and the resistance to osmotic stress. The selection of mutants was carried out among 2.5.10(5) clones survived upon plating strain SU1604 containing the sex factor F104, with a chromosome fragment carrying genes proB and proA, on solid modium with the proline analogue L-azetidine-2-carboxylate (AzT). The obtained mutant AztR clones were used as donors in replica crossing with a pro- recipient, followed by subsequent selection of AztR Pro+ exconjugants. Analysis of growth of 456 exconjugants in liquid minimal medium with NaCl at a concentration of 0.6 M helped to identify 9 mutants with increased salt tolerance, as compared with control. From these, we selected one mutant (denoted as SU1604/F'104S) which demonstrated the highest salt tolerance correlating with higher production of proline. Analysis of the mutant's properties suggests that it belongs to the group of Osm mutants.