Alone or together? A review on pure and mixed microbial cultures for butanol production

Over the past decades, biotechnological processes have significantly improved and enabled societies to move closer to a bio-based economy, no longer dependent on liquid fossil fuels. Among sustainable biofuels, biobutanol is considered the best alternative due to its high energetic content and capability of acting as a drop-in fuel for gasoline. Together with new advances in resource recovery technology, biobutanol production is now poised to become even more sustainable. This paper summarizes the research done over the past decade on biobutanol production from low-value and waste residues. Different feedstock alternatives are discussed, and the predominant biological pathways for butanol production in ABE fermentation and syngas fermentation are revisited. Particular attention is given to single and mixed culture fermentation, and how far both technologies have come to reach butanol titers close to and above the microbial toxicity level of butanol. By comparing current titers, productivities and yields of single and mixed microbial cultures, this review shows to which extent the mixed microbial culture approach can compete with pure cultures, delving further on the advantages and obstacles of each of the technologies. Based on low-value and waste residue feedstocks, clear incentives exist to use mixed microbial fermentation as the predominant production platform for butanol and to focus future research on this promising technology.