Breeding of d(-)-lactic acid high producing strain by low-energy ion implantation and preliminary analysis of related metabolism

The low-energy nitrogen ion beam implantation technique was used in the breeding of mutant d(-)-lactic-acid-producing strains. The wild strain Sporolactobacillus sp. DX12 was mutated by an N⁺ ion beam with energy of 10keV and doses ranging from 0.4 × 10¹⁵ to 6.60 × 10¹⁵ ions/cm². Combined with an efficient screening method, an efficient mutant Y2-8 was selected after two times N⁺ ion beam implantation. By using the mutant Y2-8, 121.6g/l of d-lactic acid was produced with the molar yields of 162.1% to the glucose. The yield of d-lactic acid by strain Y2-8 was 198.8% higher than the wild strain. Determination of anaerobic metabolism by Biolog MT2 was used to analyze the activities of the concerned enzymes in the lactic acid metabolic pathway. The results showed that the activities of the key enzymes responded on the substrates such as 6-phosphofructokinase, pyruvate kinase, and d-lactate dehydrogenase were considerably higher in the mutants than the wild strain. These might be affected by ion beam implantation.