Sequential fungal pretreatment of unsterilized Miscanthus: changes in composition, cellulose digestibility and microbial communities

A sequential fungal pretreatment of Miscanthus x giganteus was conducted by mixing unsterilized Miscanthus with material previously colonized with the white rot fungus Ceriporiopsis subvermispora, for three generations, each generation starting with inoculation by mixing unsterilized fresh Miscanthus with end material from the previous generation, and ending after 28 days of incubation at 28C. After the first generation, the cellulose digestibility of the material doubled, compared to the unsterilized Miscanthus, but the second and third generation showed no enhancements in cellulose digestibility. Furthermore, high degradation of Miscanthus structural carbohydrates occurred during the first generation. A microbial community study showed that, even though the fungal community of the material previously colonized by C. subvermispora was composed mainly of this fungus (>99%), by the first generation its relative abundance was down to only 9%, and other microbes had outcolonized it. Additionally, changes in the bacterial community occurred that might be associated with unwanted cellulose degradation in the system. This reiterates the necessity of feedstock sterilization for the stability and reproducibility of fungal pretreatment of lignocellulosic biomass.