Xiaoguang Liu and Shang-Tian Yang*

Department of Chemical Engineering

The Ohio State University

140 West 19th Avenue

Columbus, OH 43210

Phone: (614) 292-6611

Fax: (614) 292-3769

Email: Yang.15@osu.edu

Clostridium tyrobutyricum ATCC 25755 is an acidogenic bacterium, producing butyrate, acetate, CO₂ and H₂ as its main fermentation products. Butyric acid has many applications in chemical, food, and pharmaceutical industries. Hydrogen is a non-greenhouse gas with high energy content (about 30,000 Btus/gallon), which is an alternative to hydrocarbon fuels. Integrational mutagenesis was used to disrupt some genes in the acetic acid formation pathway in C. tyrobutyricum to enhance the production of butyrate and hydrogen. Two mutants, phosphotransacetylase gene (pta) deleted mutant (PPTA-Em) and higher hydrogen producing mutant (HydEm), were produced. Two-dimensional protein electrophoresis (2DE) was carried to study the protein expression maps of the mutants. The 2DE results showed that the protein expression patterns of the mutants were quite different from that of wild type, indicating changes of metabolic pathway in the mutants after gene manipulations. PPTA-Em and HydEm were immobilized in fibrous-bed bioreactor (FBB) to evaluate their ability to produce butyrate and hydrogen from glucose and xylose. The reactor productivity and product yield were monitored in fed-batch fermentations. The fermentation results showed that PPTA-Em produced a higher concentration (>50 g/L) of butyric acid with a higher yield (>50%) than those from the wild type. The mole ratio between hydrogen and carbon dioxide (>2) produced by HydEm was about twice of that from the wild type. These mutants immobilized in the fibrous bed bioreactor would provide an economical process to produce butyrate and hydrogen from plant biomass.