Beet molasses based exponential feeding strategy for thermostable glucose isomerase production by recombinant Escherichia coli BL21 (DE3)

BACKGROUND: The effects of pretreated beet molasses based feeding strategies on thermostable glucose isomerase (GI) production by recombinant Escherichia coli BL21 (DE3) pLysS were investigated. RESULTS: The thermostable GI encoding gene of Thermus thermophilus ( xyl A ) was recombined with pRSETA vector, and the pRSETA:: xyl A obtained was transferred into E.coli BL21 (DE3) pLysS and used for GI production. The highest soluble GI activity was obtained at t = 30 h, as A = 16 400 U L −1 (20.6 U mg −1 protein) under molasses based fed‐batch operation, with a specific growth rate µ = 0.1 h −1 (M‐0.1); on the other hand, the highest cell concentration was obtained at µ = 0.15 h −1 operation as 9.6 g L −1 at t = 32 h. The highest oxygen uptake was 4.57 mol m −3 s −1 at M‐0.1 operation. CONCLUSIONS: Molasses based fed‐batch operations were more successful in terms of cell concentration and thermostable enzyme production due to the existence of a natural sugar inducer, galactose, in the molasses composition. This study demonstrates the significance of proper feeding strategy development for over‐production of enzymes by recombinant E. coli strains.