Comparative study of changes in composition and structure during sequential fungal pretreatment of non-sterile lignocellulosic feedstocks

Fungal pretreatment with the white rot fungus Ceriporiopsis subvermispora was performed under non-sterile conditions for four different feedstocks, corn stover, miscanthus, softwood, and hardwood, using a sequential inoculation process that employed fungal-colonized feedstock as inoculum. Fungal pretreatment improved the enzymatic digestibility of unsterilized hardwood, softwood, and miscanthus after the first generation of the sequential process, increasing the glucose yield by 2-, 3- and 4.5- fold, and the xylose yield by 9-, 7- and 10- fold, respectively. However, the fungal pretreatment of unsterilized feedstocks was unsuccessful for corn stover throughout the sequential process and for all feedstocks for the second and third generation. Modifications in feedstock structure and composition were analyzed using microscopy, spectroscopy, and thermogravimetric analysis, and showed that the effects of fungal pretreatment with C. subvermispora were feedstock-dependent. A significant fungal colonization was observed in all the fungal pretreated feedstocks, but an extensive cell wall degradation was only detected in miscanthus and hardwood. Lignin-to-cellulose ratio decreased in all successful fungal pretreated feedstocks, but the lignin units (syringyl, guaiacyl, or p-hydroxyphenyl units) that were preferentially degraded varied with each feedstock. Interestingly, C. subvermispora was able to degrade terpenes from the pine resin during the fungal pretreatment of pine wood (softwood).