高非蛋白氮利用能力酵母菌的筛选与诱变

蛋白质饲料资源短缺一直是制约着中国饲料工业健康平稳发展的瓶颈问题之一。单细胞蛋白（single cell protein，SCP）在解决世界粮食与蛋白饲料短缺问题存在较大潜质。经多年研究，单细胞蛋白在菌种选育、生产工艺、发酵原料等方面均取得了较大进展，但单细胞蛋白饲料成本仍居高不下，在饲料工业中一直未得到大量应用。提高生产单细胞蛋白生产菌株非蛋白氮（non-protein nitrogen，简称NPN）利用效率和生长速度，是降低单细胞蛋白生产成本的关键。本试验从多株酵母菌中筛选出NPN利用能力较强的菌株，并对其进行紫外照射诱变，以期获得菌体蛋白产量高的突变菌株。通过对14株酵母菌对不同碳、氮源利用的研究，确定其最适碳、氮源，并依据14株酵母的生长潜力、菌体蛋白产量、NPN利用能力等进行排名，筛选出综合性能较优的酿酒酵母菌M（Saccharomyces cerevisiae strain YI59）和N2（Saccharomyces cerevisiae isolate AA2）。将酵母菌M和N2作为出发菌，进行紫外照射诱变。以葡萄糖、硫酸铵为碳、氮源，依平板菌落大小与液体发酵菌体蛋白产量进行初筛和复筛，最终获得菌落较大的3株突变菌MU23、MU3和MU5。经液体发酵复筛发现，MU3和MU5菌体蛋白含量较原出发菌M有显著提高，分别提高12.93%和11.82%（P<0.05），但菌体蛋白产量与出发菌相比无显著差异（P>0.05）；菌株MU23菌体蛋白含量与出发菌M无显著差异（P>0.05），但菌体蛋白产量较原出发菌M有较大幅度提升，为0.26 g/L，提高13.04%（P>0.05）。综合上述试验结果，使用紫外照射诱变可以达到提高酵母菌NPN利用能力和菌体蛋白产量的目的。

High Non-protein Nitrogen Utilization Capacity Yeast Screening and Mutagenesis

The shortage of protein feed resources has always been one of the bottlenecks restricting the healthy and stable development of Chinese feed industry.Single-cell proteins have great potential in solving the problem of shortage of food and protein in the world.After years of research,single-cell proteins have made great progress in strain selection,production techniques,and fermentation raw materials.However,the cost of single-cell protein feeds remains high,and has not been widely used in the feed industry.Increasing the utilization efficiency and growth rate of non-protein nitrogen (NPN) production strains for production of single cell proteins is the key to reducing the production cost of single cell proteins.In this test,strains with strong NPN use ability were screened out from multiple strains of yeast and subjected to UV irradiation to obtain mutant strains with high yeast protein yield.Through the study of 14 kinds of yeasts using different carbon and nitrogen sources,the most suitable carbon and nitrogen sources were determined.According to the ranking of the growth potential,yeast protein production and NPN utilization ability of 14 strains of yeast,yeast M(Saccharomyces cerevisiae strain YI59) and N2 (Saccharomyces cerevisiae isolate AA2) with better overall performance were screened out.Yeast M and N2 were used as starting yeast for UV irradiation mutagenesis.Using glucose,ammonium sulfate as carbon and nitrogen source,preliminary screening and rescreening were performed according to the plate colony size and the liquid fermentation cell protein production.Three strains of MU23,MU3 and MU5 with the largest colonies were finally obtained.After liquid fermentation,compared to the original yeast M,the protein contents of MU3 and MU5 were increased by 12.93% and 11.82%,respectively (P < 0.05),while the yeast protein production had no significant difference (P > 0.05);The yeast protein content of strain MU23 had no significant difference,and it's yeast protein production increased by 13.04%,reached to 0.26 g/L (P > 0.05).In conclusion,the use of ultraviolet irradiation mutagenesis could effectively improve the utilization ability of yeast NPN and the production of yeast protein.