Direct Succinic Acid Production from Non-Hydrolyzed Biomass Using Sequential Solid-State and Slurry Fermentation with Mixed Fungal Cultures

This study explores a new route for directly producing succinic acid from lignocellulosic biomass via consolidated bioprocessing technology employing lignocellulolytic and acidogenic fungal co-cultures. The consolidated bioprocessing technology involves two-stages: a solid-state fermentation pre-culturing stage followed by slurry fermentation stage. During the solid-state pre-fermentation stage, the filamentous fungi Aspergillus niger and Trichoderma reesei were co-cultured in a nitrogen-rich substrate (e.g., soy hull) to produce cellulolytic enzymes for degrading biomass cellulosic and hemicellulosic fractions to fermentable sugars. The lignolytic fungus Phanerochaete chrysosporium was grown separately on carbon-rich wood chips to induce lignolytic enzymes that degrade lignin, rendering the biomass more susceptible to cellulase attack. The solid-state pre-cultures were then combined in a slurry fermentation culture to achieve simultaneous enzymatic cellulolysis and succinic acid production. Succinic acid was generated with a maximum titer of 49.0 g/L and yield of 19.6 g succinic acid per 100 g total dry biomass substrate after 36 h of slurry fermentation. This approach is a promising alternative to conventional bacterial succinic acid production due to its minimal substrate pretreatment requirements, which could potentially reduce production costs.