The Screening Of A Thermostable α-Amlyase Producing Strain And The Study On It's Fermentation Condition And Property Of Enzyme

300 strains of bacteria isolated from soil in Tibet as the thermostable α -amylase producers, and 10 strains selected for their better secretory ability. Among them a thermophilic and alkaliphilic bacterial strain producing a large amount of thermostable α -amylase was selected. By testing morphologic and physiological-biochemical characteristics the strain was identified as Bacillus licheniformis. We call it Bacillus licheniformis Z-8.The cells of B.licheniformis Z-8 are Gram-positive and the shape of single cell is pole, and its size are 0.5-0.8 μ m× 2.0-2.5 μ m. The strain has endospore shape of which is oval. B. licheniformis Z-8 can grow in the temperature range 28-60℃ and in the salt range 0-7%. It can grow in the pH range 5-11 and its optimum pH is 7-8. The strain can make use of Glucose to produce acid. It also can make use of xylose, arabinose and mannitolum to produce acid. The result of nitrate reduction test is positive, and M.R is negative. The V.P is positive and its pH range 6.0-6.3. B.licheniformis Z-8 can make use of citrate and propionate. Its' catalase test and gelatin test are positive. It can grow with sodium azide,and can grow without NaCl and KCl.Studying on the effects of carbon sources and other influence factors optimized the protease fermentation condition for the strains. The optimal medium composition for the strain growth is(%) peptone 1%, beef extract 0.3%, NaCl 0.5% and pH 7.0. The optimal medium composition for protease producing is(%) Soyapower 0.5%, Bran 1%, soluble starch 0.25% and pH 8.8. The optimal conditions for protease producing are inoculation for 10%, seeds age for 18h, culture medium volumes for 10 mL in 100 mL flask, initial pH8.8, cultivated at 45℃ with an aeration rate of 160rpm for 48h. Then a maximum yield of 7.4 u/mL was obtained.By studying on the supernatant of the culture fluids, the enzymatic characteristics were concluded. The optimum temperature and pH for protease activity was 95℃ and pH 6.0. It was stable in the pH range 4.0-9.0 and optimum pH range 5.0-7.0. The enzyme only lost 5.4% of activity after 60 minute of heat treatment at 95℃. Addition of Ca2+ couldn't improve the themostability of enzyme. The themostability of enzyme were not depend on starch.