Microbial conversion of syngas to single cell protein: The role of carbon monoxide

Abstract

Syngas has been widely utilized as substrate in microbial processes to produce various high-value products. Nevertheless, its applicability for single cell protein (SCP) production by hydrogen-oxidizing bacteria (HOB) has never been explored. Especially, the role of carbon monoxide in SCP synthesis is unknown. Thus, this study first investigated the effect of different CO and H2 ratios in syngas on Cupriavidus necator H16 growth and SCP production. The growth of C. necator H16 was significantly restrained with the increase of CO content, and it almost ceased once the CO:H2 ratios were above 1. In addition, the growth rate of C. necator H16 increased with the increase of shaking frequency and inoculum volume. Furthermore, larger gas–liquid interfacial areas and gas input amount resulted in a higher growth rate and OD value. The raw protein contents were around 50–60% regardless of CO concentration, and the amino acid profiles showed no apparent differences. The results showed that although the presence of CO led to the reduction of the growth rate of C. necator H16, it had a limited effect on the SCP quality. H2 and CO2 in syngas were the primary substrates for SCP production, while CO served more as a toxic inhibitor. The successful demonstration of SCP synthesis from syngas may provide a superior route for the valorization of waste biomass by turning it into food or feed.