Production of Nitrilase by a Recombinant Escherichia coli in a Laboratory Scale Bioreactor

Abstract

Effects of medium pH (uncontrolled and controlled), aeration rate and agitation intensity on the production of biomass and nitrilase by a recombinant Escherichia coli in a stirred-tank bioreactor are reported. The recombinant bacterium expressed the nitrilase gene of Alcaligenes faecalis . The initial pH of the culture medium had a strong influence on the growth of biomass and enzyme production. In batch fermentation process the growth and enzyme production were maximized at 37°C with an initial medium pH 7.0. The fermentation was influenced by oxygen transfer efficiency of the bioreactor and by the turbulence regimen. The optimal production conditions were an aeration rate of 0.4 vvm and an agitation speed of 400 rpm. Higher values of agitation speed and aeration rate proved detrimental to both biomass production and nitrilase activity. Under optimal conditions, the final dry biomass concentration was 6.9 g/L and the biomass specific enzyme activity was 58 U/g dry cells.