Fermentations with new recombinant organisms

United States fuel ethanol production in 1998 exceeded the record productio n of 1.4 billion gallons set in 1995. Most of this ethanol was produced fro m over 550 million bushels of corn. Expanding fuel ethanol production will require developing lower-cost feedstocks, and only lignocellulosic feedstoc ks are available in sufficient quantities to substitute for corn starch. Ma jor technical hurdles to converting lignocellulose to ethanol include the l ack of low-cost efficient enzymes for saccharification of biomass to fermen table sugars and the development of microorganisms for the fermentation of these mixed sugars. To date, the most successful research approaches to dev elop navel biocatalysts that will efficiently ferment mixed sugar syrups in clude isolation of novel yeasts that ferment xylose, genetic engineering of Escherichia coli and other gram negative bacteria for ethanol production, and genetic engineering of Saccharoymces cerevisiae and Zymomonas mobilis f or pentose utilization. We have evaluated the fermentation of corn fiber hy drolyzates by the various strains developed. E. coli K011, E. coli SL40, E. coli FBR3, Zymomonas CP4 (pZB5), and Saccharomyces 1400 (pLNH32) fermented corn fiber hydrolyzates to ethanol in the range of 21-34 g/L with yields r anging from 0.41 to 0.50 g of ethanol per gram of sugar consumed. Progress with new recombinant microorganisms has been rapid and will continue with t he eventual development of organisms suitable for commercial ethanol produc tion. Each research approach holds considerable promise, with the possibili ty existing that different "industrially hardened" strains may find separat e applications in the fermentation of specific feedstocks.