Submitted to: Applied Microbiology and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/23/2003
Publication Date: 8/8/2003
Citation: Lopez, M.J., Nichols, N.N., Dien, B.S., Moreno, J., Bothast, R.J. 2004. Isolation of microorganisms for biological detoxification of lignocellulosic hydrolysates. Applied Microbiology And Biotechnology. 64:125-131. Interpretive Summary: Fibrous biomass, such as wheat straw and corn stover, is a potential feedstock for producing fuel ethanol. When converting fibrous biomass to ethanol, the first step is to break down the fibers to their constituent sugars or to render them readily digestible by enzymes. The freed sugars are next fermented to ethanol using microorganisms, such as yeast. However, breaking down the fibers releases other chemicals that inhibit the fermentation. These chemicals include organic acids, aromatics, and furans. We have isolated novel microorganisms that grow on these inhibitors and, thereby, can be used to reduce their concentration prior to fermentation. Treating material with microorganisms to reduce the concentration of unwanted chemicals is termed bio-abatement and has been successfully applied to treating contaminated soils and industrial waste water discharges. This work is the first time microorganisms have been used for bioabatement of inhibitors in treated biomass. This research is expected to benefit farmers and agricultural processors by making the conversion of agricultural material to fuel ethanol a more viable process.
Technical Abstract: In this study, we isolated new microorganisms for depletion of inhibitors in lignocellulosic acid hydrolysates. A sequential enrichment strategy was used to isolate microorganisms from soil. Selection was carried out in a defined mineral medium containing a mixture of ferulic acid (5 mM), 5-hydroxymethylfurfural (5-HMF, 15 mM), and furfural (20 mM) as the carbon and energy sources, followed by an additional transfer into a corn stover hydrolysate (CSH) prepared using dilute acid. Subsequently, based on stable growth on these substrates, six isolates including five bacteria related to Methylobacterium extorquens, Pseudomonas sp, Flavobacterium indologenes, Acinetobacter sp., Arthrobacter aurescens, and one fungus, Coniochaeta ligniaria, were chosen. All six isolates depleted toxic compounds from defined medium, but only C. ligniaria C8 (NRRL30616) was effective at eliminating furfural and 5-HMF from CSH. The enrichment protocol and selection criteria led to the isolation of a microorganism for the abatement of inhibitors in lignocellulosic hydrolysates. Acid pretreatment of lignocellulosic biomass releases furan and phenolic compounds, which are toxic to microorganisms used for subsequent fermentation. C. ligniaria NRRL 30616 may be useful in developing a bioprocess for inhibitor abatement in the conversion of lignocellulosic biomass to fuels and chemicals.