Beet molasses-based feeding strategy enhances recombinant thermostable glucose isomerase production by Escherichia coli BL21 (DE3).

The aim of this work was to develop an effective fed-batch feeding strategy to enhance recombinant glucose isomerase (r-GI) production by recombinant Escherichia coli BL21 (DE3) pLysS on an industrially relevant feedstock without the application of an exogenous inducer. Following the batch operation (0 < t < 7 H), the effects of pulse and/or continuous feeding of hydrolyzed beet molasses were investigated under five different feeding strategies. The two most promising strategies with respect to r-GI activity were (i) PM-0.05, designed with one pulse feed (t = 7 H) followed by a continuous feed and (ii) 2PMF -0.05, designed with two consecutive pulse feeds (t = 7 and 10 H) followed by a continuous feed. The continuous feeding of molasses for both fermentation strategies employed the same precalculated feeding rate, μo = 0.05 H-1 . The maximum r-GI activities exhibited by PM-0.05 and 2PMF -0.05 were 29,050 and 30,642 U dm-3 , respectively. On the one hand, compared to PM-0.05 r-GI activity reached its maximum within a shorter cultivation time (∆tmax = 2 H) at 2PMF -0.05, which could be preferable in terms of manufacturing costs and possible risks; on the other hand, PM-0.05 is a simpler fermentation regime compared to 2PMF -0.05 with respect to manipulations that should be considered in large-scale production.