Bioconversion of CO2 Using Immobilized Whole-Cell Catalyst with Periplasmic Carbonic Anhydrase

Abstract

Recently, as a mimic of the natural biomineralization process, the use of carbonic anhydrase (CA), which is an enzyme catalyzing fast hydration of carbon dioxide (CO2), has been suggested for capture and conversion of anthropogenic greenhouse gas CO2. There have been many researches on production of recombinant CA in bacterial cells and immobilization of CA onto various solid supports. Previously, whole-cell catalyst with periplasmic recombinant CA has been suggested as an economical strategy. Periplasmic whole-cell catalyst can i) contribute to enzyme stability, ii) eliminate costly enzyme purification steps, and iii) ensure high enzymatic activity compared to cytoplasmic whole-cell system. In spite of these advantages, there are some limitations of utilization of whole-cell catalyst such as limited reusability and modest improvement of stability. Thus, immobilization process is needed to overcome these limitations and use in practical application. In this study, we constructed periplasmic whole-cell catalysts with Hydrogenovibrio marinus CA (hmCA) which has higher stability at high temperature and high salt concentration than bovine erythrocyte CA (bCA). We immobilized the whole cells (pCA) in polyurethane foam to maximize the practical applicability by improving reusability and stability. Immobilization of whole-cell was confirmed through images of optical microscope and CO2 hydration activity of whole-cell immobilized in PUF (pCA-PUF). Activity of pCA-PUF was optimized by several factors for practical application such as changing signal peptide, cell concentration and surface area of PUF. We found that immobilization efficiency of whole-cells was higher than that of purified hmCA. We also showed that pCA-PUF has high reusability and thermal stability compared to the bare whole-cell catalyst. Finally, CO2 gas conversion tests in lab-scale and pilot-scale by 1-ton reactor demonstrated that pCA-PUF can be an effective, economical catalyst for practical CO2 capture and conversion.