INDUSTRIALLY ROBUST ENZYMES AND MICROORGANISMS FOR PRODUCTION OF SUGARS AND ETHANOL FROM AGRICULTURAL BIOMASS
Location: National Center for Agricultural Utilization Research
Title: BUTANOL PRODUCTION FROM AGRICULTURAL RESIDUES: IMPACT OF DEGRADATION PRODUCTS ON CLOSTRIDIUM BEIJERINCKII GROWTH AND BUTANOL FERMENTATION
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: April 22, 2005
Publication Date: April 23, 2005
Citation: Ezeji, T., Qureshi, N., Blaschek, H.P. 2005. Butanol production from agricultural residues: impact of degradation products on Clostridium beijerinckii growth and butanol fermentation [abstract]. World Congress on Industrial Biotechnology and Bioprocessing. p. 163.
As a result of prohibitive cost of use of corn starch as substrate, we have focused our research on the use of agricultural residues for butanol production by fermentation using Clostridium beijerinckii BA101, a genetically modified, hyper-butanol producing strain. With this aim, we are focusing on the potential use of corn stover, corn fiber, and fiber-rich distillers dried grains and solubles (DDGS) as the substrates for cell growth and butanol production. Corn fiber represents a renewable resource that is available in significant quantities from the corn dry and wet-milling industries. Approximately 4.7 x 10**6 dry tons of corn fiber are produced in the United States annually. Corn fiber contains about 69% fermentable sugars, of which approximately 20, 14, and 35% are associated with the starch, cellulose, and hemicellulose fractions, respectively. Typically, 4.5 lb of corn fiber are obtained from a bushel (56 lb) of corn, which can be converted to about 3.0 lb of fermentable sugars.
Although the research on genetics, fermentation, upstream processing, and downstream processing has progressed significantly, the clostridia are not able to efficiently hydrolyze fiber-rich agricultural residues. For this reason, agricultural biomass should be hydrolyzed to simple sugars using economically developed methods. Use of dilute sulfuric acid is one of the pretreatment methods that can be applied to agricultural residues to bring about hydrolysis. Unfortunately, during acid hydrolysis, lignins are oxidized or degraded to form phenolic compounds, and part of the sugars that are released during hydrolysis are also degraded into products that inhibit cell growth and fermentation. Examples of sugar degraded inhibitory compounds include furfural and hydroxymethyl furfural (HMF), and examples of phenolics include ferulic, glucuronic, rho-coumaric acids, etc. Organic acid, such as acetic acid, is produced in significant amounts during acid hydrolysis of agricultural residues.
We have investigated the effect of some of these inhibitors on C. beijerinckii BA101 growth and butanol fermentation. Among the aldehydes (furfural, HMF, and syringaldehyde) tested, syringaldehyde was found to minimally inhibit cell growth of C. beijerinckii BA101, while there was strong inhibition of butanol production at a concentration range of 0.3–3.0 gL**-1. When 0.3 gL**-1 rho-coumaric and ferulic acids were introduced into the fermentation medium, growth and AB production by C. beijerinckii BA101 decreased by >24 and 92%, respectively. At 0.3 gL**-1 glucuronic acid, AB production by C. beijerinckii BA101 decreased by approximately 10% and subsequently decreased to 30% when the concentration was increased to 3.0 gL**-1. In contradiction to these inhibitors, inclusion of acetate into the fermentation medium increased AB production by more than 19%, consistent with our earlier work.