Coproduction of thermostable amylase and beta-galactosidase enzymes by Geobacillus stearothermophilus SAB-40: aplication of Plackett-Burman design to evaluate culture requirements affecting enzyme production.

: A locally isolated thermophile, Geobacillus sp. SAB-40, producing thermostable extracellular amylase constitutively and an induced intracellular beta-galactosidase was characterized and identified based on 16S rRNA sequencing. A phylogenetic analysis then revealed its closeness to Geobacillus stearothermophilus. To evaluate the effect of the culture conditions on the coproduction of both enzymes by G. stearothermophilus SAB-40, a Plackett-Burman fractional factorial design was applied to determine the impact of twenty variables. Among the tested variables, CaCl2, the incubation time, MgSO4.7H2O, and tryptone were found to be the most significant for encouraging amylase production. Lactose was found to promote beta-galactosidase production, whereas starch had a significantly negative effect on lactase production. Based on a statistical analysis, a preoptimized medium attained the maximum production of amylase and beta-galactosidase at 23.29 U/ml/min and 12,958 U/mg biomass, respectively, which was 3- and 2-fold higher than the yield of amylase and lactase obtained with the basal medium, respectively.