Autotrophic Production of the Sesquiterpene α-Humulene with Cupriavidus necator in a Controlled Bioreactor

Abstract

Cupriavidus necator is a facultative chemolithotrophic organism that grows under both heterotrophic and autotrophic conditions. It is becoming increasingly important due to its ability to convert CO2 into industrially valuable chemicals. To translate the potential of C. necator into technical applications, it is necessary to optimize and scale up production processes. A previous proof-of-principle study showed that C. necator can be used for the de novo production of the terpene α-humulene from CO2 up to concentrations of 11 mg L−1 in septum flasks. However, an increase in final product titer and space–time yield will be necessary to establish an economically viable industrial process. To ensure optimized growth and production conditions, the application of an improved process design in a gas bioreactor with the control of pH, dissolved oxygen and temperature including a controlled gas supply was investigated. In the controlled gas bioreactor, the concentration of α-humulene was improved by a factor of 6.6 and the space–time yield was improved by a factor of 13.2. These results represent an important step toward the autotrophic production of high-value chemicals from CO2. In addition, the in situ product removal of α-humulene was investigated and important indications of the critical logP value were obtained, which was in the range of 3.0–4.2.