Effect of Aeration Rate on the Biotransformation of Cortexolone Using Cunninghamella elegans in a Laboratory Scale Bioreactor

A single-step microbial transformation process for the production of cortisol and prednisolone from cortexolone (Reichstein's compound S) using Cunninghamella elegans cells in an aerated fermentor was investigated. The biotransformation process was carried out using 5 l stirred tank bioreactor. The effect of pH values, aeration rate, cell dry weight and cortexolone feeding strategy were investigated. At aeration rate of 1 v/v/m the total bioconversion efficiency (TBE) was 57%, at 48 h time course, cell dry weight 1.42 g/100 ml and the residual glucose was 3 g/l. On increasing the aeration rate up to 2 v/v/m, the products yields were increased up to 79.2%. The medium pH was maintained to constant 6.5 till the end of fermentation. The fermentation was influenced by oxygen transfer efficiency of the bioreactor and the cell dry weight was increased up to 3.58 g/100 ml after 48 h, accompanied by a sharp decrease of residual glucose to 4.14 g/l. At the first fed batch, the highest yields of cortisol and prednisolone (52.2% and 34.03%, respectively) were obtained.