Power to terpenoids: a two-stage bioprocess for CO2 utilization based on integrating microbial electrosynthesis and yeast cultivation.

Climate change associated with the rising global CO2 emissions is poised to trigger disastrous consequences. Various approaches, ranging from technological developments to policies, are being considered to reduce rising emissions and prevent its associated impacts. One of the emerging CO2 utilization technologies is microbial electrosynthesis (MES), where microbes are used as catalysts to convert CO2 and electricity into multi-carbon compounds. Although it offers a number of advantages over other CO2 utilisation technologies, inability to produce high-value chemicals has become a significant barrier to the technology's economic viability. This study intends to show that two bioprocesses, MES and yeast cultivation—can be linked to produce high-value terpenoids from CO2 and electricity. At an applied Ecathode of -1.2 V (versus Ag/AgCl), Clostridium ljungdahlii, a well known acetogen is used to convert CO2 to acetic acid (up to 1.18 g/l) in MES reactor. In the second stage, sclareol (C20) and ß-carotene (C40) are produced separately using recombinant Saccharomyces cerevisiae strains using the produced acetic acid as feedstock. The production of yeast biomass was also tested in the second process using non-recombinant S. cerevisiae strain. With the unpurified spent medium from MES reactors, S. cerevisiae produced 0.32 ± 0.04 mg/l ß-carotene, 2.54 ± 0.91 mg/l sclareol, and 369.66 ± 41.67 mg/l biomass. According to the primary economic analysis, it is possible to produce sclareol and biomass using recombinant and non-recombinant S. cerevisiae, respectively by directly using the unpurified acetate-containing spent media MES reactor. This proof of concept study can be a promising CO2 conversion platform for high value chemical synthesis. With further optimization and scale-up research, this two step bioprocess approach has the potential to offer an economically viable CO2 utilization solution.