ENRICHMENT AND ISOLATION OF AUXOTROPHIC MUTANTS OF HYDROGENOMONAS H 16

1. Using cells of Hydrogenomonas H 16 after mutagenesis by nitrous acid about 0.4 percent and by 1-nitroso-3-nitro-1-methylguanidine 1.5 percent auxotrophic mutants were found among the survivors. In order to increase the mutant yield an enrichment method was elaborated. The penicillin technique was modified by replacing penicillin by colistine, since penicillin is ineffective for Hydrogenomonas H 16. The incubation of 108 cells/ml under growth conditions in the presence of 50 μg colistine/ml for 10 hrs was found effective; during a model experiment 88 percent of the non-growing auxotrophic cells and only 0.09 percent of the growing wildtype cells survived. 2. 214 mutants were isolated and nutritionally characterized. In addition to auxotrophs many mutants were isolated which lack the ability to utilize fructose. 3. Some of the strains requiring isoleucine, or isoleucine+valine were characterized. On the basis of results of crossfeeding experiments and of enzyme assays it is concluded that the biosynthetic pathways for isoleucine and valine in Hydrogenomonas are the same as in other bacteria. © 1969 Springer-Verlag.