Sugar-based feedstocks or oil-rich crops are primarily used in today?s biofuel industry. These biofuel production approaches pose a threat to the global food supply. As an alternative, this research will use inexpensive lignocellulosic biomass (e.g., corn stover or switchgrass) as a feedstock for producing biofuel. The conversion process proposed is based on the gasification of the biomass into syngas (mainly CO, CO2 and H2), and the subsequent fermentation of those gaseous molecules into fuels (such as ethanol). The objectives of this project aim to address two important fundamental issues in syngas fermentations: 1. the mass transfer limitations of transporting gaseous substrates (CO, CO2 and H2) into microbes; 2. the bottleneck enzymes in microbes to convert syngas into biofuels. This study will advance the current research on syngas fermentation using methods in systems biology. By linking macroscopic syngas mass transfer conditions to intracellular enzyme reaction rates in biofuel producing microbes, a holistic view of syngas fermentation will be provided. Ultimately, this project will also produce guidelines for developing other gas-to-liquid biorefineries.
Transient 13C techniques and metabolic models will be used to examine syngas mass transfer and biological utilization by Clostridium carboxidivorans. The first task will incorporate 13C tracing to accurately determine gas-liquid mass transfer parameters and analyze their influence on cellular carbon assimilation. The second task will be to develop a flux balance model to predict microbial growth and ethanol production in response to bioreactor control parameters, such as gas flow rate and mixing. The third task will include pilot scale syngas fermentation at the flux-model-predicted conditions. This project will determine the mass transfer coefficient (KLa) of different syngas composition under complex fermentation conditions, and improve the understandings of the bioavailability of gaseous substrates under various bioreactor operations. Meanwhile, 13C-assisted flux balance analysis will also reveal key enzymatic reactions, which control syngas bioconversion into ethanol. The combination of a metabolic flux model with gas-liquid mass transfer dynamics will offer rational approaches for further work in syngas fermentation development. This research is a partnership between Iowa State University and Washington University in St. Louis. The PIs, with their complementary skills, will provide excellent training and interdisciplinary educational opportunities (including summer research, workshop, international studies, etc.) for students to study reaction engineering, bioprocessing, analytical chemistry, and metabolic modeling.
