Breeding Glucoamylase Production Stains By Mutation

The Aspergillus niger was mutated by UV?DES and compound mutation methods to improve glucoamylase activity.LZ9?LZ160?LZ173?ZW47?ZW85?LZL13were obtained after preliminary screening and re-screening,which had higher glucoamylase activity.ZW47 had a genetic stability in these strains,whose glucoamylase activity increased from 8104 U/mL to 9070 U/mL in the fifth day.The influence of mycelium incubation time,osmotic stabilizer,enzymes composition,enzymatic reaction time on preparation and regeneration of A.niger protoplast was researched.The formation procedure of A.niger protoplast was observed under the phase contrast microscope.The protoplast was prepared under the optimal conditions that the mycelia incubated for 4 days were treated with 0.5%snailase and 0.5%cellulose for 3 hours in 0.6 mol/L NaCl osmotic stabilizer.The suitable regeneration medium contain 0.2%yeast,0.5%peptone,0.2%NaCl,1%starch,0.1%CaCl2,0.1%MgSO4·5H2O.The mutate strains doesn't have genetic stability by protoplasts mutation.