In-situ Product Recovery as a Strategy to Increase Product Yield and Mitigate Product Toxicity

Abstract

Product inhibition is often the cause limiting the maximum product concentration attainable in fermentation. This study showed the product yield of p-cresol could be improved by in-situ product recovery (ISPR). Escherichia coli transformed with the hpd BCA operon from Clostridium difficile was shown in this study to express phydroxyphenylacetate decarboxylase which converted p-hydroxyphenylacetate into p-cresol under anaerobic fermentation. Toxicity of p-cresol found at a concentration as low as 5 mM in a broth spiked with p-cresol was shown to have limited the maximum product concentration at 1 ± 0.1 mM after 30 hours of batch fermentation. Product yield was however shown to increase by 51% when activated carbon was used to remove p-cresol in-situ production. The activated carbon concentrated p-cresol on the solid adsorbent which was subsequently separated by sedimentation and p-cresol recovered by ultrasonic-assisted solvent extraction. Desorption of p-cresol from the spent activated carbon allowed the adsorbent to be regenerated for further product recovery. The ISPR strategy reported here was shown to improve the yield of a toxic product, was sustainable, and when adapted to a continuous process would increase productivity.