RESEARCH ARTICLE


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



Yuen Ling Ng*, Yi Yang Kuek
Department of Chemical and Environmental Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom


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© 2013 Ng and Kuek

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 International Public License (CC-BY 4.0), a copy of which is available at: (https://creativecommons.org/licenses/by/4.0/legalcode). This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

* Address correspondence to this author at the Department of Chemical and Environmental Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, United Kingdom; Tel: +44(0)115 951 3770; Fax: +44(0)115 951 4115; E-mail: yuen.ng@nottingham.ac.uk


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.

Keywords: adsorption, Escherichia coli, glycyl radical enzyme, in-situ product recovery, p-cresol, product toxicity.