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Improvements were found in the inosine productivity of Brevibacterium ammoniagenes KY 13714, which is an adenine leaky and 6-mercaptoguanine resistant mutant. A highly productive mutant, KY 13761, was selected after the addition of 6-methylthiopurine resistance and guanine requiring character to KY 13714 and after repeating single colony isolation.

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Various wild and mutant strains of bacteria, yeasts, actinomycetes and fungi (total 1416 strains) were cultured in a medium containing DL-glyceric acid (10 mg/mi), L-threo nine (10 mg/ml) or glycine (5 mg/ml).As a result, Nocardia butanica ATCC 21197, Nocardia paraffinica ATCC 21198 and Brevibacterium ketoglutamicum ATCC 15587 were found to accumulate 1 mg/ml of L-serine in the broth. These 3 strains were belonged to a group of microorganisms which were weak in L-serine decomposition activity, although most microorganisms decomposed over 90% of the L-serine into some compounds other than glycine.Some microorganisms produced a-aminobutyrate, L-isoleucine or glycine from L-threonine.

Summary. L-Threonine hyper-producing mutants were obtained from Escherichia coli W strain KY-8366, by reducing L-threonine degradation activity and enhancing L-threonine biosynthetic activity. An L-threonine degradation reaction test using resting ceils of KY-8366 suggested that the main pathway of L-threonine degradation by KY-8366 is via glycine. A strain with reduced L-threonine degradation activity was obtained among those mutants that could not utilize L-threonine as sole nitrogen source. Rifampicin-resistant mutants and L-lysine plus methionine-insentitive mutants were isolated. These mutants showed enhanced aspartokinase levels and accumulated more L-threonine than the parental strains. Mutant H-4290 accumulated 58 g/l of L-threonine.