Low-energy ion implantation is a new mutation source, which has the characteristic of light damage, high mutation rate, and a broad spectrum mutation. In order to obtain industrial strain with high L-(+)-lactic acid yield, the original strain Lactobacillus casei CICC6028 was mutated by nitrogen ion beam implantation. It was found that the original strain had a higher positive mutation rate when the output power was 10keV and the dose of N+ implantation was 50×2.6×1013 ions/cm2. The mutant N-2 was obtained for many times screening and its yield of L-(+)-lactic acid was 136 g/L which was improved by 38.8% compared with the original strain whose yield of L-(+)-lactic acid was 98g/L as the cultivation time was 120h. The initial screening methods were also studied in this work but it was found that the transparent halos method was unavailable, so the initial screening was performed by shake flask fermentation. HPLC chromatogram was used to analyse the purity of L-(+)-lactic acid that was produced by the mutant strain N-2, and the result indicated the main production of N-2 was L-(+)-lactic acid and there was no other acid almost.
With ion implantation, a high xylanase-producing strainAspergillus nigerBU99 was selected. Different late acting carbon sources (wheat bran, wheat straw, corncob and bagasse) had an effect on enzymatic production. Additionally, it was found that fast acting carbon sources (lactose, galactose, sucrose, glucose and maltose) put into the media affected on xylanase production too. Severe catabolic repression was observed in the media with lactose, but other sugars (galactose, sucrose, glucose and maltose) could increase the production of xylanase compared with the control. The production of xylanase was improved too when corncob flour was hydrolyzed by α-amylase, cellulase or/and glucoamylase. Additionally, it was found that the production of xylanase would be almost higher at 60h when the media contained glucose or were hydrolyzed by enzymes.
The paper studied on parameters of ion implantation into lipid producing strain Rhodotorula glutinis and lipid extration technology. It was found that the strain had a higher positive mutation rate when the output power was 10keV and the dose of N+ implantation was 80×2.6×1013 ions/cm2. Then a high-yield mutant strain D30 was obtained and it’s lipid yield which was 3.10 g/L increased by 33.05% than that of the original. Additionally, statistically-based experimental designs were applied for the optimization of lipid extraction by acid-heating coupling ultrasonic technique. By a Plackett-Burman design, it was found that three factors, treatment time of HCl (p=0.036) , ultrasonic time (p=0.0105) and rate of extracting solution (VCHCl3:VCH3OH) (p=0.0105), had significant effect on lipid extraction. Subsequently, these significant factors were optimized using response surface methodology (RSM), and the optimized parameters of lipid extraction were as follows: 34 min for treatment time of HCl, 7.5 min for ultrasonic treating time, 1.9:1 for rate of extracting solution (VCHCl3:VCH3OH). Finally the fermentation characteristic of high-yield mutation strain D30 was studied, when fermentation time was 10 d, it’s lipid yield increased to 7.81 g/L
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