Strain improvement of Rhizopus oryzae for over-production of lactic acid by random mutations

Rhizopus oryzae mutant strain LA-UN-1 was isolated from the lactic acid-producing strain NRRL 395 by mutagenesis with both ultraviolet (UV) irradiation and nitrosoguanidine (NTG) treatment with the aim of selecting mutant in pellet form. One of the mutants in flask culture easily formed the pellet morphology at a diameter between 1.1 and 1.3 mm. In this case, the lactic acid concentration reached 59.5 g/l, which was 54.5% higher than that of the wild type. This investigation indicates that the production of L-lactic acid could be enhanced with the method of mutagenesis.   Key words: Lactic acid, morphology, mutagenesis, Rhizopus oryzae.