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Basic facts: Cellulose is the most abundant biopolymer and renewable energy source on Earth. Moreover, cellulose is a major component of agricultural and municipal waste. The decomposition of cellulose, which is carried out almost exclusively by microorganisms, is a key step in the cycling of carbon in the biosphere. Vast quantities of cellulose and other plant polysaccharides are degraded in anoxic environments where decomposition is effected by fermenting microbes, primarily species of Clostridium. In recent years, cellulolytic clostridia have received considerable attention because of their potential use in processes that involve the direct conversion of cellulosic biomass to fuels such as ethanol. Increased use of biomass fuels is a promising option to decrease our dependence on foreign oil while reducing greenhouse emissions. Clostridium phytofermentans is an anaerobic ethanol- and hydrogen-producing cellulolytic bacterium from forest soil that is capable of fermenting all major carbohydrate components of biomass. Cellulose, pectin, starch, and xylan are rapidly degraded and fermented with ethanol and hydrogen formed as major metabolic products. Phylogenetically, C. phytofermentans is a member of Cluster XIVa of the low-G+C-content Gram-positive bacteria, only distantly related to Clostridium thermocellum , a cellulose-fermenting microbe with draft genome sequence determined by the DOE Joint Genome Institute. Genomic comparisons of these two cellulolytic anaerobes may prove especially informative with respect to their polymer-hydrolyzing life styles. C. phytofermentans is of particular interest for the production of high concentrations of ethanol during cellulose fermentation. Two to four times more ethanol than acetate are formed, suggesting that C. phytofermentans possesses unusual fermentation pathways. Hydrogen production approaches maximum amounts expected based on the amounts of non-gaseous products formed. Moreover, C. phytofermentans is amenable to genetic manipulation. Genomic analyses and associated research strategies will advance understanding of complex processes involved in the degradation of abundant plant biopolymers, and allow researchers to develop practical applications for C. phytofermentans , including the bioconversion of cellulose-containing municipal wastes and agricultural products to fuels such as ethanol and hydrogen. Literature reference: Warnick, T. A., B. A. Methé, and S. B. Leschine. 2002. Clostridium phytofermentans sp. nov., a cellulolytic mesophile from forest soil. Int. J. Syst. Evol. Microbiol. 52: 1155-1160. |
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