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.