Taurocyamine-utilizing mutants from a wild-type strain of Pseudomonas

Pseudomonas sp. ATCC 14676 produces glycocyaminase (EC 3.5.3.2) and guanidinobutyrase (EC 3.5.3.7). Taurocyamine (2-guanidinoethane sulfonate) is a gratuitous inducer of both of these amidinohydrolases. Mutants of this organism capable of utilizing taurocyamine as a nitrogen source were isolated directly from the wild-type cells after uv irradiation or treatment with N-methyl-N'-nitro-N-nitrosoguanidine; frequencies of mutations observed under appropriate conditions were above 10(-7). Strain U2-3-3, which was selected from the 11 isolated taurocyamine-utilizing strains, was proved to be derived from the wild-type strain. Both taurocyamine and 4-guanidinobutyrate were able to induce an enzyme of strain U2-3-3 that liberated urea from taurocyamine, whereas glycocyamine failed to induce the system. The activity of the enzyme toward taurocyamine was found to be about one-third of that toward guanidinobutyrate when both taurocyamine and guanidinobutyrate were used as inducer. These observations suggest that the enzyme of the mutant capable of hydrolyzing taurocyamine has emerged from guanidinobutyrase of the wild-type strain which hydrolyzes taurocyamine at a very low rate, probably as a result of a point mutation in the structural gene.