Fermentations with New Recombinant Organisms

Abstract

United States fuel ethanol production in 1998 exceeded the record production of 1.4 billion gallons set in 1995. Most of this ethanol was produced from over 550 million bushels of corn. Expanding fuel ethanol production will require developing lower-cost feedstocks, and only lignocellulosic feedstocks are available in sufficient quantities to substitute for corn starch. Major technical hurdles to converting lignocellulose to ethanol include the lack of low-cost efficient enzymes for saccharification of biomass to fermentable sugars and the development of microorganisms for the fermentation of these mixed sugars. To date, the most successful research approaches to develop novel biocatalysts that will efficiently ferment mixed sugar syrups include 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 for pentose utilization. We have evaluated the fermentation of corn fiber hydrolyzates 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 ranging 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 the eventual development of organisms suitable for commercial ethanol production. Each research approach holds considerable promise, with the possibility existing that different "industrially hardened" strains may find separate applications in the fermentation of specific feedstocks.

Progress and perspective on lignocellulosic hydrolysate inhibitor tolerance improvement in Zymomonas mobilis

“…Compared with the results with pure sugars, ethanol productions in hydrolysates were impeded significantly (Bothast et al 1999;Feng et al 2012;Jennings and Schell 2011;Jeon et al 2010;Joachimsthal et al 1999;Krishnan et al 2000;Mohagheghi et al 2002Mohagheghi et al , 2004Schell et al 2016;Serate et al 2015;Teixeira et al 2000;Yanase et al 2012;Zhao et al 2014). For example, the ethanol yield was much lower in the hydrolysate (15 g/L) than in pure glucose fermentation (44.9 g/L) (Dong et al 2013;Zhao et al 2014).…”

Developing Organisms for Consolidated Bioprocessing of Biomass to Ethanol

“…The S. cerevisiae strain developed by the Mascoma Corporation represents the best CBP organism engineered thus far as this strain could convert several cellulosic substrates to ethanol with addition of minimal exogenous enzymes in an SSF configuration (Mcbride et al, 2010). Compared to S. cerevisiae, all of the bacterial species discussed above are relatively sensitive to inhibitors associated with lignocellulosic hydrolysates (Bothast et al, 1999;Yamano et al, 1998;Ohta et al, 1991b). Engineering enhanced protein secretion allowed the successful secretion of endoglucanases in E. coli (Ji et al, 2009) and K. oxytoca ).…”

“…Strain development is therefore the most important technical obstacle towards the conversion of lignocellulose to commodity products in a CBP configuration (Bothast et al, 1999;Alfenore et al, 2002). Organisms with broad substrate ranges and cellulolytic and/or hemicellulolytic abilities generally suffer from poor growth characteristics or poor product producing characteristics.…”

Next-generation cellulosic ethanol technologies and their contribution to a sustainable Africa

“…Strain development is therefore the most important technical obstacle towards the conversion of lignocellulose to commodity products in a CBP configuration [26,27]. Organisms with broad substrate ranges and cellulolytic and/or hemicellulolytic abilities generally suffer from poor growth characteristics or poor product-producing characteristics.…”