Mutation Screening Of High-yield Protein Strain By Heavy Ion Beam And Optimization Of Fermentation Conditions

Candida utilis is a very important microorganism in industry, often used to produce a variety of useful biological substance, it was certified as a food additive by FDA of Amercia and it was used as livestock feed in many countries. In recent years, it was widely used to the production of protein feed by fermentation and straw feed. Candida utilis is one of the most widespread microorganism in the production of biological feed.In this study, Mutation screening of this strain and optimization for growth conditions are studied, the experiment aimed at obtainning a strain with high protein producing and stable nature,finding its better growth and fermentation conditions and making it applied in the production of protein feed by taking advantage of industrial and agricultural waste and sideline products.In this study, Candida utilis (No. GSICC-50350) stored in the laboratory acted as the start strain, using heavy ion radiation mutation screening techniques to obtain a high protein producing strain. Previous researchers made use of a variety of mutation methods in order to obtain the strain with high-yield protein, but yeast is Higher fungus, has strong repair capacity and resistance to the usual mutagen. general mutagens can not achieve good mutagenic effects, thus, we chose the heavy ion beam produced by Lanzhou Heavy Ion heavy ion accelerator as a new source of radiation mutation breeding, which has large energy、strong mutagenic effect, and weaker repaire ability. The good results was achieved through mutagenesis and screening, the results showed:1.The study maked use of heavy ion irradiation to mutate the strain-Candida utilis, to screen high-yield strain, we achieved the best result that the ion implantation irradiation is40Gy. Under this conditions, the protein content and the strain thallli biomass is relatively higher, which supplied the theoretical basis for further use of Candida utilis by heavy ion irradiation mutagenesis. By means of heavy ion irradiation, the strain with high-yield protein is screened, which was numbered P-2-B, Compared with the treatment before mutation, the protein content was38.26%. increased by0.91times than19.99%before mutation, the experiment showed the strain has stable nature (subculture nine times and protein test).2.This study researched the effect of temperature, speed, organic and inorganic nitrogen sources, inorganic salts, amino acids and other factors on the growth of this strain, further optimization of fermentation conditions by single factor test and orthogonal experiment showed the optimum conditions were:training culture temperature was30℃, shaking speed was180r/min, the content of fermentation inoculum was10%, the best fermentation time was32h, under such conditions, the protein content was42.20%.3.This study also used the main start strain-mutant Candida utilis combined with Aspergillus Niger、Candida tropicalis and Saccharomyces cerevisiae to producesingle cell protein feed by substepsolid fermentation of pumace, through the multi-strains vaccination in phases and the optimization for culture methods, inoculum dose, fermentation temperature co-fermentation time, solid-liquid ratio and pH, we obtained the optimization processes technologyby. The single factor test and orthogonal experiment releved the optimization fermentation condition is material: water=60%, the initial pH5.5,30℃, Aspergillus niger inoculum dose7.5%, composite yeast inoculum dose10%, and Aspergillus niger was inoculated at the beginning of the fermentation, composite yeast liquid was inoculated in24h after fermentation, co-culture time was72h.. Under optimum the ratio of strains and fermentation conditions, the crude protein content in fermentation end-product increased from4.97%to27.60%, increased by22.63%, achieved high quality protein feed standards.