Enhanced production of d -lactic acid by Sporolactobacillus sp.Y2-8 mutant generated by atmospheric and room temperature plasma

To improve the production of d-lactic acid, atmospheric and room temperature plasma (ARTP) was used to generate mutations in Sporolactobacillus sp. Y2-8. An efficient mutant YBS1-5 was rapidly isolated by implanting ARTP twice with a 100 W radio-frequency power input, 10 standard liters per minute of the helium flow, and a 2 mm treatment distance. Significant improvement of d-lactic acid productivity (1.39 g L^-1 H^-1) by YBS1-5 was achieved, and it was 41.84% higher than the productivity (0.98 g L^-1 H^-1) of Y2-8. Moreover, the dry cell weight of YBS1-5 was 16.7% higher than that of Y2-8. Metabolic activities of concerned substrates related with key enzymes of d-lactic acid fermentation were analyzed by Biolog approach. Results showed that the activities of the key enzymes glucokinase and d-lactate dehydrogenase in mutant YBS1-5 were increased by approximately 45% and 66%, respectively, in comparison with those of the strain Y2-8. Fed-batch fermentation further improved the productivity; 127 g L^-1 d-lactic acid in 74 H by YBS1-5 with higher productivity (1.72 g L^-1 H^-1) was achieved. The subculture experiments indicated that YBS1-5 was genetically stable after eight generations.