One-step production of C6\u2013C8 carboxylates by mixed culture solely grown on CO

Pinjing He,Liming Shao,Wenhao Han,Fan Lü

doi:10.1186/s13068-017-1005-8

Abstract

BackgroundThis 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.ResultsThe 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.ConclusionsThese 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.

Highlights

This study aimed at producing C6–C8 medium-chain carboxylates (MCCAs) directly from gaseous CO using mixed culture
Products of anaerobic fermentation from waste, i.e. short-chain carboxylic acids (SCCAs) and alcohols, can be converted to more valuable mediumchain carboxylic acids (MCCAs), such as n-caproate and n-caprylate, by mixed culture under anaerobic conditions, and this reaction is known as chain elongation [1, 2]
Zhang et al [15] got MCCAs production from mixture of C O2 and H2 by mixed culture, which belongs to syngas components

Summary

Introduction

This study aimed at producing C6–C8 medium-chain carboxylates (MCCAs) directly from gaseous CO using mixed culture. Products of anaerobic fermentation from waste, i.e. short-chain carboxylic acids (SCCAs) and alcohols, can be converted to more valuable mediumchain carboxylic acids (MCCAs), such as n-caproate and n-caprylate, by mixed culture ( called “open culture” or “reactor microbiomes”) under anaerobic conditions, and this reaction is known as chain elongation [1, 2]. Gildemyn et al [8] converted real syngas fermentation He et al Biotechnol Biofuels (2018) 11:4 effluent into MCCAs in continuous fermentation using pure culture of Clostridium kluyveri, which is one of the known model organisms for chain elongation. Richter et al [10] used coculture of carboxydotrophic Clostridium ljungdahlii and chain-elongating C. kluyveri to produce MCCAs and corresponding alcohols. Compared to bio-converted C O2 and H2, CO is the most toxic and becomes the limitation for the utilization of syngas by mixed culture

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