Biodegradation kinetics and modeling of whey lactose by bacterial hemoglobin VHb-expressing Escherichia coli strain

The batch fermentation of cheese whey lactose was achieved using Escherichia coli:pUC8:16 recombinant strain that was transformed with Vitreoscilla hemoglobin gene(vgb). In this process, 70% of the initial whey lactose was biodegraded during 24 h Of incubation time. Biodegradation was accompanied with a turnover of glucose intermediate and a production of lactic acid, Total lactic acid produced by this recombinant strain was 57.8 mmol/L compared with a reference lactic acid producing strain. Lactobacillus acidophilus, that yielded only 55.3 mmol/L. of lactic acid from the same initial whey lactose concentration. The engineering of vgb gene transformation in E. coli strain has led to increase in bacterial biomass and boosted lactic acid production, relative to Other strains that lack the vgb gene like E coli:pUC9 or E. coli wild type or Enterobacter aerogenes. Contrary to Monod's, Haldane's model gave a good fit to the growth kinetics data. Kinetic constants of the Haldane equation were mu(m) = 0.5573 h(-1), K-s = 4.8812 g/L, K-l = 53.897 g/L. Biomass growth was well described by the logistic equation while Luedeking-Piret equation defined the product formation kinetics. Substrate consumption was explained by production rate and maintenance requirements. In Simulation studies including the Haldane model, an evident agreement was observed between measured and calculated biomass, product, and substrate concentrations. (C) 2009 Elsevier B.V. All rights reserved.