l(+)-Lactic acid production by co-fermentation of glucose and xylose with Rhizopus oryzae obtained by low-energy ion beam irradiation

Low-energy ion beam irradiation (10-200 keV) has been proved to have a wide range of biological effects in recent years. When Rhizopus oryzae PW352 was irradiated with a 15-keV low-energy ion beam an L(+)-lactic acid high-yield mutant, RQ4015, was obtained. When 150 g/l glucose was used as the sole carbon source, L(+)-lactic acid of RQ4015 reached 121 g/l after 36 h shake-flask cultivation. However, the highest lactic acid concentration 74 g/l was obtained when 100 g/l xylose was present in the medium as the sole carbon source. When mixed xylose (25 g/l) and glucose (75 g/l) were present in a bubble column, L(+)-lactic acid production of RQ4015 reached 83 g. A high mutation rate and a wide mutation spectrum of low-energy ion implantation were observed in the experiment, suggesting that ion implantation can be a highly efficient mutagenic means for microorganism breeding in many commercial applications.