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 (xylA) was recombined with pRSETA vector, and the pRSETA::xylA 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 L1 (20.6 U mg1 protein) under molasses based fed-batch operation, with a specific growth rate mu = 0.1 h1 (M-0.1); on the other hand, the highest cell concentration was obtained at mu = 0.15 h1 operation as 9.6 g L1 at t = 32 h. The highest oxygen uptake was 4.57 mol m3 s1 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. (c) 2012 Society of Chemical Industry