Viable strategies for enhancing acetone-butanol-ethanol production from non-detoxified switchgrass hydrolysates

A process engineering strategy was investigated towards developing a viable scheme for effective conversion of hydrothermolysis pretreated non-detoxified switchgrass hydrolysates (SH) to acetone butanol ethanol (ABE) using a metabolically engineered strain of Clostridium beijerinckii NCIMB 8052, C. beijerinckii_AKR. The engineered strain was modified by homologous integration into the chromosome and constitutive expression of Cbei_3974, which encodes an aldo-keto reductase. Intermittent feeding strategy was employed in which fermentation was initiated with 30% of the SH and the remaining 70% SH was added when the optical density (OD600nm) of C. beijerinckii attained 0.5. The ABE (14.9 g/L) produced from non-detoxified SH by the inhibitor tolerant C. beijerinckii_AKR was comparable to the P2-glucose control medium (14.7 g/L). Using intermittent feeding, wildtype and C. beijerinckii_AKR produced similar amounts of ABE (about 17.5 g/L). This shows that intermittent feeding strategy and C. beijerinckii_AKR enhanced ABE fermentation and eliminated the need for SH detoxification prior to fermentation.

Automated summary

The study investigated a process engineering strategy to effectively convert hydrothermolysis pretreated non-detoxified switchgrass hydrolysates to acetone butanol ethanol (ABE) using a metabolically engineered strain of Clostridium beijerinckii. Through modifications to the engineered strain and the use of intermittent feeding, ABE fermentation was enhanced and detoxification of the hydrolysates prior to fermentation was eliminated. The ABE production from the non-detoxified hydrolysates by the engineered strain was comparable to the control medium, demonstrating the potential of this strategy in improving biofuel production.