Geobacillus sp. 4j, a deep-sea high-salt thermophile, was found to produce thermostable α-amylase. In this work, culture medium and conditions were first optimized to enhance the production of thermostable α-amylase by statistical methodologies. The resulting extracellular production was increased by five times and reached 6.40 U/ml. Then, a high-temperature batch culture of the thermophile in a 15 l in-house-designed bioreactor was studied. The results showed that a relatively high dissolved oxygen (600 rpm and 15 l/min) and culture temperature of 60°C facilitated both cell growth and α-amylase production. Thus, an efficient fermentation process was established with initial medium of pH 6.0, culture temperature of 60°C, and dissolved oxygen above 20%. It gave an α-amylase production of 79 U/ml and productivity of 19804 U/l·hr, which were 10.8 and 208 times higher than those in shake flask, respectively. This work is useful for deep-sea high-salt thermophile culture, where efforts are lacking presently.
Keywords: Geobacillus; high-temperature bioreactor; statistical methodologies; thermophile.