[Isolation of auxotrophic mutants of Rhodopseudomonas sphaeroides]

A collection of stable auxotrophic mutants with a frequency of reversions to the wild type below 10(-8) was obtained from the wild strain of Rhodopseudomonas sphaeroides 2R under the action of nitrosoguanidine or nitrosomethylurea. The mutants required methionine, leucine, arginine, histidine, tryptophan and cytosine for their growth. Mutants carrying 2 or 3 auxotrophic labels in their genome were selected from the primary auxotrophs under the action of UV (lambda = 254 nm). The paper describes a semi-enriched medium in which the diameter of prototrophic colonies reaches 5 mm while that of auxotrophic colonies does not exceed 1-2 mm. The selection of microcolonies from this medium makes it possible to increase the yield of auxotrophs several times as compared with the technique of imprints.