One-step production of C6-C8 carboxylates by mixed culture solely grown on CO.

Background: This study aimed at producing C6-C8 medium-chain carboxylates (MCCAs) directly from gaseous CO using mixed culture. The yield and C2-C8 product composition were investigated when CO was continuously fed with gradually increasing partial pressure.

Results: The maximal concentrations of n -caproate, n -heptylate, and n -caprylate were 1.892, 1.635, and 1.033 mmol L-1 , which were achieved at the maximal production rates of 0.276, 0.442, and 0.112 mmol L-1 day-1 , respectively. Microbial analysis revealed that long-term acclimation and high CO partial pressure were important to establish a CO-tolerant and CO-utilizing chain-elongating microbiome, rich in Acinetobacter , Alcaligenes, and Rhodobacteraceae and capable of forming MCCAs solely from CO.

Conclusions: These results demonstrated that carboxylate and syngas platform could be integrated in a shared growth vessel, and could be a promising one-step technique to convert gaseous syngas to preferable liquid biochemicals, thereby avoiding the necessity to coordinate syngas fermentation to short-chain carboxylates and short-to-medium-chain elongation. Thus, this method could provide an alternative solution for the utilization of waste-derived syngas and expand the resource of promising biofuels.