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Effects of bioreactor operation parameters on intracellular reaction rate distribution in beta-lactamase production by bacillus species

Arifoğlu, Müge
In this study, the effects of oxygen transfer (OT) on beta-lactamase production and on intracellular reaction rates were investigated with Bacillus licheniformis ATCC 2597. In order to clarify the oxygen transfer effects on the production of beta-lactamase, firstly a glucose based defined medium was designed and using this medium, the effects of bioreactor operation parameters, i.e., pH and temperature, on beta-lactamase activity and cell formation were investigated in laboratory scale batch-bioreactors using shake bioreactors having V=33 ml working volumes. Among the investigated bioprocess conditions, the highest beta-lactamase activity was obtained as A=115 U cm-3, in the medium with 7.0 kg m-3 glucose, 7.1 kg m-3 (NH4)2HPO4 and the salt solution, at pH0=7.5, T=37C, N=200 min-1. At the optimum conditions found in laboratory scale the effects of OT on cell generation, substrate consumption, product (beta-lactamase) and by-products formations were investigated at three different air inlet (Q0/ VR = 0.2, 0.5 and 1 vvm) and at three agitation rates (N=250, 500, 750 min-1) in V = 3.0 dm3 batch bioreactors consisting of temperature, pH, foam, stirring rate and dissolved oxygen controls. Along with the fermentation, cell, substrate and by-product concentrations, beta-lactamase activity, yield coefficients, specific rates, oxygen uptake rates and the liquid phase mass transfer coefficient values were determined. The highest beta-lactamase activity was obtained at 0.5 vvm 500 min-1 and at 0.2 vvm 500 min-1 conditions as ca. A=90 U cm-3 while the highest cell concentration was obtained as Cx=0.67 kg m-3 at 0.5 vvm 750 min-1 and at 0.2 vvm 750 min-1 conditions. KLa, increased with the increase in the agitation and aeration rates and its values varied between 0.007-0.044 s-1 and oxygen uptake rate varied between 0.4-1.6 mol m-3 s-1. Finally, the influence of OT conditions on