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.