Oxidized Extracellular Electron Shuttles (Quinones) Increase Biobutanol Production
Anne Haluska, University of Illinois at Urbana-Champaign, Urbana, IL
Xiaofeng Ye, University of Illinois at Urbana-Champaign, Urbana, IL
Kevin Finneran, University of Illinois at Urbana-Champaign, Urbana, IL

Extracellular Quinone/Hydroquinones Increase Bio-Hydrogen and Bio-Solvent Production (Butanol and Acetone) in Growing and Resting Cells of Clostridium beijerinckii
Xiaofeng Ye, University of Illinois at Urbana-Champaign, Urbana, IL
Kevin T. Finneran, University of Illinois at Urbana-Champaign, Urbana, IL

Oxidized Extracellular Electron Shuttles (Quinones) Increase Biobutanol Production 

Student Presenter

Anne Haluska, University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering, 4162 Newmark Civil Engineering Lab, 205 N. Mathews Avenue, Urbana, IL 61801
Xiaofeng Ye, University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering, 4162 Newmark Civil Engineering Lab, 205 N. Mathews Avenue, Urbana, IL 61801
Kevin Finneran, University of Illinois at Urbana-Champaign, Department of Civil and Environmental Engineering, 4162 Newmark Civil Engineering Lab, 205 N. Mathews Avenue, Urbana, IL 61801

The current administration has emphasized sustainable energy as a key component of their strategy to reduce CO₂ emissions which contribute to climate change and to limit dependence on fossil fuels.  Biofuels like butanol produced during fermentation of plant biomass, are one renewable energy option.  Butanol holds several advantages over ethanol because of its low miscibility with water, low volatility, higher energy content and ability to replace gasoline without any modification of current vehicles. However, microbial butanol tolerance is low, limiting the final product yield of bio-butanol.  Higher butanol yields are needed to make butanol recovery easier so that butanol is a competitive biofuel option. 

This research focuses on increasing butanol production through addition of extracellular electron shuttles which alter electron transport pathways in Clostridium beijerinckii fermentation.  Oxidized electron shuttles (quinones) were introduced at concentrations ranging from 100µM to 5mM; millimolar anthraquinone-2,6-disulfonate (AQDS) increased butanol yield between 2.5 and 5 times in C. beijerinckii cultures as compared to unamended controls.  C. beijerinckii cultures with millimolar AQDS and 30 g/L glucose produced final butanol yields (g/g) equal to final yields of unamended C. beijerinckii cultures with 2 times the substrate concentration (60 g/L glucose).  Both hydrogen yield and butyric acid yield decreased in the presence of AQDS.   An electron mass balance showed that as butanol equivalents increase, butyric acid equivalents decrease.  This was used to understand the mechanism behind the shift in fermentative pathways in the presence of AQDS.  The conceptual model for explaining the switch from butyric acid to butanol as the major fermentation product is that AQDS acts as an extracellular electron sink that “switches” total carbon and electron flow to butanol production.

Extracellular Quinone/Hydroquinones Increase Bio-Hydrogen and Bio-Solvent Production (Butanol and Acetone) in Growing and Resting Cells of Clostridium beijerinckii

Student Presenter

Xiaofeng Ye, University of Illinois, at Urbana-Champaign, Urbana, IL, Email: ye3@illinois.edu 
Kevin T. Finneran, University of Illinois, at Urbana-Champaign, Urbana, IL, Email: finneran@illinois.edu

Biofuels are considered a sustainable alternative to fossil fuels for electric power and possibly motor vehicles, and the incoming administration has made sustainable energy a hallmark of its energy policy.  Bio-butanol and Bio-H₂ are considered two reasonable energy carriers that result from the fermentation of plant biomass.  However, the yields of both of these fermentation products are limited by fermentative microbial metabolism.  To increase yields of these biofuels mutant strains must be developed or more efficient reactor systems must be engineered.  We have utilized extracellular quinones/hydroquinones to alter electron transport in the fermentative microorganism Clostridium beijerinckii.  Past data demonstrated increased H₂ production when electrons were delivered as anthrahydroquinone disulfonate (AH₂QDS).  Current data indicate that 250-1000µM AH₂QDS decreased doubling times and increased total biomass with glucose (10mM) as the primary substrate.  AH₂QDS also increased the rate of glucose consumption.  H₂ increases were due to increased total biomass coupled to direct AH₂QDS oxidation to H₂ during the acidogenic phase of C. beijerinckii growth.  During the solventogenic phase AH₂QDS decreased butanol production to nearly zero relative to controls.  However, the oxidized form anthraquinone disulfonate (AQDS) increased butanol production by approximately 5 times relative to unamended controls.  AH₂QDS increased acetone production, while AQDS did not.  AH₂QDS was oxidized during the acidogenic phase, and AQDS was reduced during the solventogenic phase.  This electron cycling influenced growth, hydrogen production, and butanol production.  This is currently being utilized to a) determine the mechanisms by which the cycle influences the fermentative pathway, and b) increase total biofuel yield.  A chemostat has been used to increase total bio-hydrogen and bio-solvent production, and hydroquinones have increased H₂ production rates by two to three times unamended operation.  Metabolic modeling based on free energy of all reaction pathways is being used to identify how quinones shift output of fermentation products.

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