Butanol and caproate production by consolidated bioprocessing after adaptive evolution of a fermentative microbial community

Abstract

Butanol production from cellulose by consolidated bioprocessing may accelerate the commercialization of lignocellulosic biofuels. This study applied adaptive evolution to a natural microbial community consisting of different taxa of fermenters and plant‐degrading bacteria to increase its production of butanol. To this end, the parental microbial community was subjected to the stepwise enrichment of butanol at four initial concentrations in repeated‐batch fermentations using pretreated corn stover as the sole substrate. After the adaptive evolution, the microbial community exposed to the highest concentration of butanol produced 13.8 g L‐1 butanol, which was nine times higher than the parental microbial community. The adapted microbial community also produced the medium‐chain fatty acid caproate (7.5 g L‐1) from the condensation of alcohols (ethanol/butanol) with short‐chain fatty acids at the end of the fermentation. A network analysis revealed that the largest subcommunities were represented by Clostridium sensu stricto 7 and Caproiciproducens, which are associated with the production of alcohols (ethanol/butanol) and medium‐chain fatty acids, respectively. In the smaller subcommunities, Pseudomonas, Sutterella, and Pandoraea became more important after adaptive evolution, suggesting the production of extracellular polymeric substances and cross‐stress protection as mechanisms of protection and adaptation against butanol. This study demonstrated that butanol production by the consolidated bioprocessing of cellulose required solventogenic bacteria, diverse taxa of plant‐degrading bacteria that established unique interactions with the fermenters and, more important, members with mechanisms of protection and tolerance to solvents.