Conversion of ammonia-pretreated switchgrass to biofuel precursors by bacterial–fungal consortia under solid-state and submerged-state cultivation

Aim: The aim of this study was to develop and evaluate bacterial–fungal communities to deconstruct switchgrass to biofuel precursors. Methods and Results: Bacterial–fungal consortia, mesophilic (25°C) and thermophilic (50°C), were enriched from switchgrass bales from which enzyme mixtures were used to deconstruct delignified switchgrass (DSG). The bacterial–fungal consortia were able to produce enzymes including endoglucanase, exoglucanase, β-glucosidase, xylanase, xylosidase and pectinase to convert DSG to soluble carbohydrates. 454 pyrosequencing revealed that Paenibacillus and Streptomyces were the dominant bacteria in the mesophilic and thermophilic consortia respectively. Penicillium and Acremonium were the dominant fungi in the mesophilic consortia, whereas Aspergillus and Penicillium were the dominant fungi present in the thermophilic consortia. Conclusions: The results show that the state of cultivation, solid-state or submerged-state, affects the community structure as well as enzyme activities produced by these bacterial–fungal consortia. The enzyme mixture produced by the bacterial–fungal consortia released a higher amount of xylose than glucose during saccharification of DSG. Significance and Impact of the Study: The study provides a novel approach to produce enzymes for conversion of lignocellulolytic feedstocks to soluble sugars which can be used to produce biofuel precursors.