Isopropanol production from carbon dioxide in Cupriavidus necator in a pressurized bioreactor

Abstract

A bioreactor was designed to provide high gas mass transfer to reach cell and product titres in the g L^-1 level from CO₂ for realistic, laboratory scale, engineered autotrophic strain evaluation. The design was based on independent CO₂, H₂ and air inputs and the ability to operate at high pressures. The bioreactor configuration and cultivation strategy enabled growth of Cupriavidus necator strains for long periods, to reach over 3 g L^-1 dry cell weight. No negative impact of the high pressure was observed on viability of the strains up to more than 4 bar overpressure. The cultivation was then carried out using an engineered isopropanol producing strain; in this case, 3.5 g L^-1 isopropanol was obtained from CO₂ as the sole carbon source. This is the first reported demonstration of a successful production from engineered bacteria of product in the g L^-1 range on CO₂, raising the prospect of future development of CO₂-based bioprocesses.

Keywords: Autotrophy; Bioreactor design; Carbon dioxide; Cupriavidus necator; Gas fermentation; Hydrogen; Isopropanol; Pressure; Ralstonia eutropha.