Enhanced biotransformations and product recovery in a membrane bioreactor through application of a direct electric current

Abstract

The simultaneous enhancement of biotransformation coupled to product recovery, purification and concentration is presented. The nitrilase of Rhodococcus rhodochrous LL100-21 catalyses the single-step hydrolytic biotransformation of benzonitrile to benzoic acid and ammonia. When a direct electric current is applied across a bioreactor containing the bacterium and benzonitrile, the charged product (benzoic acid) can be removed in situ across an anion exchange membrane and recovered in a separate compartment. Over the course of a 24-hour biotransformation, benzonitrile was converted to benzoic acid which was completely removed from the bioreactor chamber and concentrated 3-fold in a separate chamber. The rate of production of benzoic acid increased by 42% when the current was applied (0.044 mmol/min/g dry cell weight in the presence of current as compared to 0.03 mmol/min/g dry cell weight in its absence). The enhanced reaction rate was achieved irrespective of product separation and therefore appears to be a direct effect upon the bacterial cells. This process has potential for enhanced productivity from biotransformations through a simultaneous increase in metabolic activity and in situ product recovery.