Breeding Of Citric Acid Producing Bacteria By Low Energy Ions Implantation

Low-energy ion implantation has been considered as a new kind of mutation breeding and foreign gene delivery techniques. By the means of implanting low-energy ions into organisms, the biological effects and the function mechanisms of the technique were investigated by some researchers. Although the researchers have observed some biological effects and revealed some basic mechanisms since the past decade, they do not master the roles of low-energy ion implantation, and the studies on the law of inheritance in the microorganism irradiated by low-energy metal ions has not been reported so far. The mutagenic effect of Aspergillus niger strains by low energy ion implantation has been studied. The regulation of the interaction between low energy ion and microbe is primarily investigated. In our experiments, choosing the Aspergillus niger as the target of low-energy ion implantation, we observed and counted the biological effects of the Aspergillus niger,to make the fundaments for exploring the interaction between low-energy ions and complicated organisms further. At the same time by strain breeding high-yielding Aspergillus niger we made an improvement in the productivity of citric acid. First of all, the best Aspergillus niger was screening from factory preserved bacterium after rejuvenating, culturing and filtrating. Then we chose N1-2 as the original stain for mutation. we studied several chief factors that could impact on the yield of citric acid and optimized the culturing and fermentation conditions. By doing experiments we optimized the quantity of culture flask as 500ml and seed as one loop of the inoculator, fermentation time as 67-69 hours, and the speed of the shaking flask as 300r/min,while fermentation temperature as 37℃. Then we studied its character of bearing the irradiated with UV,counted the biological effects of the Aspergillus niger, and chose the high-yielding mutant stain named 10min-3 whose yield of citric acid was been increased by 5.33% as the beginning Aspergillus niger waiting for farther irradiated with low-energy ions. In this paper, we chiefly discussed the biological effects after implanting low-energy ions into the Aspergillus niger. We studied the interaction between low-energy ions and Aspergillus niger by irradiating it with different energy, doses and different kinds of ions. Then we compared the different mutagenic effects of Aspergillus niger irradiated with UV and low-energy ions. The results show that the Aspergillus niger by ion implantation can achieve higher rate of mutation and wide mutational spectrum. 　Two high yield Aspergillus niger mutant strains has been bred from this. Through 15KeV N+,258×1013ions/cm2 implanting on citric acid producing bacteria, two high-yield mutant strains named (S)N15KeV 4-1 and (S)N15KeV 4-17 were obtained. The yield of citric acid is increased by 13.31% and 12.40% respectively. The results show that the mutant strains have high genetic stability.