Seminar Presentation

Please join us for seminar Monday November 10 presented by Marian Cromwell entitled “Synthetic Biology Approaches for Overcoming the Roadblocks to Achieving Higher Biobutanol Titers with Clostridium beijerinckii NCIMB 8052” 

Time: 12:05-12:55

Location: Room 205, Babcock Hall 

ABSTRACT

Biobutanol is a promising biofuel and an important industrial chemical with numerous applications. However, commercial production of biobutanol is hampered by low titers and high cost of feedstock. Clostridium beijerinckii NCIMB 8052 (Cbei) is a natural producer of butanol and a model organism for studying biobutanol production. Cbei can utilize sugars from diverse sources including lignocellulosic biomasses (LB). This study seeks to address the two challenges to biobutanol production: (a) low titer, and (b) high cost of feedstock. Low butanol titer stems from tight wiring of butanol biosynthesis in Cbei and emerging results suggest that cyclic-di-adenosine monophosphate (c-di-AMP) is a key player that likely serves as a nimble cellular ‘leash’ restricting butanol biosynthesis. Overexpressing disA and pdewhose protein products synthesize and hydrolyze c-di-AMP, respectively, in Cbei, led to near-complete inhibition of butanol and acetone biosyntheses in this organism. Enzyme activity assays also showed complete inhibition of enzymes involved in solvent biosynthesis. Despite their promise as cheap feedstocks for biobutanol production, pretreatment of LB to release fermentable sugars generates inhibitory compounds that negatively impact fermentation. To address this, site-directed mutagenesis was deployed to engineer an aldo-keto reductase (AKR) previously shown to detoxify LB-derived inhibitors. The goal was to switch cofactor preference from NADPH to the more abundant NADH. This led to an AKR variant with ~25% improved inhibitor detoxification with NADH as cofactor. In summary, characterizing c-di-AMP-mediated control of butanol biosynthesis and overexpressing the improved AKR variant in Cbei hold promise for overcoming the prime challenges to economical butanol production.