GENETIC AND BIOCHEMICAL STUDIES ON 5′-NUCLEOTIDE FERMENTATION

I. NUCLEOTIDE DEGRADING ABILITY OF BACILLUS SUBTILIS AND DERIVATION OF MUTANTS DEVOID OF THIS ABILITY

Abstract

Both strains K and M, belonging to B. subtilis, were found to possess 5′-nucleotide degrading activity. However, strain M was characterized by the fact that the formation of degrading enzyme(s) was well repressed by inorganic phosphate in contrast to strain K. The strong activity in strain C-30, an inosine producing mutant belonging to K, was suggested to be localized outside the cell membrane.
A mutant MX-46, which was derived from a purine auxotroph belonging to M, showed no growth response to 0.2μmoles/ml of 5′-IMP and has nonspecifically lost 90% of the nucleotide degrading activity as well as alkaline phosphatase activity of the wild strain. On the other hand, alkaline phosphatase negative mutants derived independently from strain M still possessed 15-20% of nucleotide degrading activity of the wild strain. Therefore, it was concluded that MX-46 was different from normal alkaline phosphatase negative mutants.
A pur⁺-transformant MT-16, derived from MX-46 via MX-97, accumulated four mononucleotides in the culture medium. An adenine requiring mutant, MX-7, derived from MT-16, did not accumulate IMP, and a try⁺-transductant MT-11 derived from MX-7, which had partially acquired the degrading activity, accumulated IMP together with hypoxanthine. The relationship between the bacterial degrading activity and the accumulation of nucleotide was discussed in view of these observations.