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.

Membranes in Biotechnology

“…The cocurrent (of about 16 A m -1 ) resulted in a 42 % increase in the conversion rate. The authors believe that the cells (and consequently the enzymatic activity) are stimulated due to the current introduced [57].…”

Electro-extractive fermentation for efficient biohydrogen production

“…The flanking membranes (CSM and BP) prevent direct contact between bacterial cells and the electrodes, as the extremes of pH at the electrode surfaces would result in unwanted reactions (Li et al, 2004;Mustacchi et al, 2005). The BP membrane also splits water, generating H + on the cathode side and OH -on the anode side, a function exploited to provide pH control simultaneously during extractive fermentations (Wong et al, 2010).…”

The effect of whole cell immobilisation on the biotransformation of benzonitrile and the use of direct electric current for enhanced product removal

“…They kept the nearelectrode areas separate from compartments M and MA, to avoid extremes of pH and unwanted electrochemical reactions. The reactor configuration has been described in detail previously (Mustacchi et al, 2005), but is summarised in Figure 1.…”

“…Product recovery costs normally represent 60%-70% of the total production costs (Zeikus et al, 1999). Consequently, the combined use of electrokinetics (or electrodialysis) has been developed to aid product separation within bioprocesses (Li et al, 2004;Mustacchi et al, 2005).…”

“…In the present project, an integrated membrane system is used for the continuous separation of charged acids by electrodialysis as they are produced in the bioreactor by nitrilase-catalysed hydrolysis. Previous study has shown that the electric current elicited a 42% increase in biotransformation rate, irrespective of whether the product was separated or not (Mustacchi et al, 2005). The system has also been applied to the whole-cell fermentation of glucose to lactic acid, in which relief of end-product inhibition was also achieved (Li et al, 2004).…”