Effects of pretreated beet molasses on benzaldehyde lyase production by recombinantEscherichia coliBL21(DE3)pLySs

Abstract

To investigate the effects of pretreated-beet molasses on Escherichia coli fermentation using benzaldehyde lyase (BAL) production by recombinant E. coli BL21(DE3)pLySs process as the model system. The effect of the initial pretreated (hydrolysed) beet molasses concentration was investigated at 16, 24, 30 and 56 g l(-1) at a dissolved oxygen condition of 40% air saturation cascade to airflow, at N = 625 min(-1) and pH(C) = 7.2 controlled-pH operation conditions. The highest cell concentration and BAL activity were obtained as C(X) = 5.3 g l(-1) and A = 1617 U cm(-3), respectively, in the medium containing 30 g l(-1) pretreated beet molasses consisting of 7.5 g l(-1) glucose and 7.5 g l(-1) fructose. Production with and without IPTG (isopropyl-beta-d-thiogalactopyranoside) induction using the medium containing 30 g l(-1) of pretreated beet molasses yielded the same amount of BAL production, where the overall cell yield on the substrate was 0.37 g g(-1), and the highest oxygen transfer coefficient was K(L)a = 0.048 s(-1). Pretreated beet molasses was used in the fermentation with E. coli for the first time and it yielded higher cell and BAL production compared with the glucose-based medium. Pretreated beet molasses was found to be a good carbon source for E. coli fermentation. Furthermore, IPTG addition was not required to induce recombinant protein production as galactose, one of the monomers of trisaccharide raffinose present in the beet molasses (1.2%), induced the lac promoter.