Cheng-Shung Gong

Ethanol Production from Renewable Resources

Vast amounts of renewable biomass are available for conversion to liquid fuel, ethanol. In order to convert biomass to ethanol, the efficient utilization of both cellulose-derived and hemicellulose-derived carbohydrates is essential. Six-carbon sugars are readily utilized for this purpose. Pentoses, on the other hand, are more difficult to convert. Several metabolic factors limit the efficient utilization of pentoses (xylose and arabinose). Recent developments in the improvement of microbial cultures provide the versatility of conversion of both hexoses and pentoses to ethanol more efficiently. In addition, novel bioprocess technologies offer a promising prospective for the efficient conversion of biomass and recovery of ethanol.

Production of multifunctional organic acids from renewable resources.

Recently, the microbial production of multifunctional organic acid has received interest due to their increased use in the food industry and their potential as raw materials for the manufacture of biodegradable polymers. Certain species of microorganisms produce significant quantities of organic acids in high yields under specific cultivation conditions from biomass-derived carbohydrates. The accumulation of some acids, such as fumaric, malic and succinic acid, are believed to involve CO2-fixation which gives high yields of products. The application of special fermentation techniques and the methods for downstream processing of products are described. Techniques such as simultaneous fermentation and product recovery and downstream processing are likely to occupy an important role in the reduction of production costs. Finally, some aspects of process design and current industrial production processes are discussed.

Quantitative production of xylitol from D-xylose by a high-xylitol producing yeast mutant Candida tropicalis HXP2

SummaryXylitol was produced as a metabolic by-product by a number of yeasts when grown on medium containing D-xylose as carbon and energy sources. Among the yeast strains tested, a mutant strain of Candida tropicalis (HXP2) was found to produce xylitol from D-xylose with a high yield (>90%). Ethanol was also produced by HXP2 when D-glucose, D-fructose, or sucrose were used as substrates. The high-xylitol-producing yeast mutant is a good organism for the production of xylitol from biomass that contains D-xylose.

Cellulase and Biosynthesis Regulation

Publisher Summary The conversion of cellulosic materials to useful products has attracted a great deal of attention in recent years, because of the growing need for energy, food, and chemicals, and also for more acceptable means of municipal waste treatment. There have been many studies on the utilization of cellulosic materials by ways of saccharification and fermentation to produce food and fuel. Enzymatic hydrolysis of cellulose to produce fermentable sugars is an attractive method of active current interest. Over the years, cellulolytic enzymes have been studied in great detail. Most of the research has focused upon the production, screening, and mutation to develop high cellulase producing microorganisms. However, understanding of enzyme kinetics, the mode of action of cellulases, as well as the regulation of cellulase production is of special importance for large scale enzyme production and for enzymatic saccharification of cellulose. This chapter discusses the regulation of cellulase synthesis in cellulolytic organisms. It also discusses about cellobiohydrolase, which is the major cellulase produced by T. reesei and perhaps, also by some other mycelial fungi.

Ethanol production from corn cob pretreated by the ammonia steeping process using genetically engineered yeast

SummaryA new and effective pretreatment process for biomass conversion involves the steeping of biomass in 2.9 M NH4OH. This resulted in the removing about 80–90% of the lignin along with almost all the acetate from cellulosic residues. Based on dry cellulose from corn cob, a high glucose yield of 92% was obtained after enzymatic saccharification of cellulose fraction. By using a genetically engineered, xylosefermenting Saccharomyces 1400(pLNH33) in the batch fermentation of a glucose-xylose mixture from corn cob, an ethanol concentration of 47 g/L was obtained within 36 h with 84% yield. In addition, an ethanol concentration of 45 g/L was obtained within 48 h with 86% yield using simultaneous saccharification-fermentation process.

Direct fermentation of cellulose to ethanol by a cellulolytic filamentous fungus, Monilia sp.

SummaryA saprophytic filamentous fungus, Monilia sp., isolated from bagasse compost was found to utilize many polysaccharides (including cellulose) and to produce cellulases and hemicellulases. Monilla sp. also fermented glucose, xylose and cellulosic materials to ethanol. Over 60% of the solid cellulose substrate added to Monilia sp. cultures was converted to ethanol as the major fermentation product. These results indicate that Monilia sp. is a potential organism for the direct conversion of cellulosic biomass to ethanol.

Ethanol production from pentoses and sugar-cane bagasse hemicellulose hydrolysate by Mucor and Fusarium species

Abstract The fermentation of carbohydrates and hemicellulose hydrolysate by Mucor and Fusarium species has been investigated, with the following results. Both Mucor and Fusarium species are able to ferment various sugars and alditols, including d -glucose, pentoses and xylitol, to ethanol. Mucor is able to ferment sugar-cane bagasse hemicellulose hydrolysate to ethanol. Fusarium F5 is not able to ferment sugar-cane bagasse hemicellulose hydrolysate to ethanol. During fermentation of hemicellulose hydrolysates, d -glucose was utilized first, followed by d -xylose and l -arabinose. Small amounts of xylitol were produced by Mucor from d -xylose through oxidoreduction reactions, presumably mediated by the enzyme aldose reductase 1 (alditol: NADP + 1-oxidoreductase, EC 1.1.1.21). For pentose fermentation, d -xylose was the preferred substrate. Only small amounts of ethanol were produced from l -arabinose and d -arabitol. No ethanol was produced from l -xylose, d -arabinose or l -arabitol.

Effect of oxygen uptake rate on ethanol production by a xylose-fermenting yeast mutant,Candida sp. XF217

SummaryThe fermentation of D-xylose by theCandida sp. mutant XF217 was studied at different oxygen uptake rates by controlling dissolved oxygen tension or agitation rate. The ethanol yield increases as the oxygen uptake rate decreases. The ethanol production rate is maximized at an oxygen uptake rate of 9–12 millimole/L/hour. Xylitol and cell mass production and cell morphology are also affected by oxygen level.

Bioconversion of Fumaric Acid to Succinic Acid by Recombinant E. coli

Succinic acid was produced efficiently from fumaric acid by a recombinant E. coli strain DH5 alpha/pGC1002 containing multicopy fumarate reductase genes. The effects of initial fumaric acid and glucose concentration on the production of succinic acid were investigated. Succinic acid reached 41 to over 60 g/L in 48.5 h starting with 50 to 64 g/L fumaric acid. Significant substrate inhibition was observed at initial fumaric acid concentration of 90 g/L. L-Malic acid became the major fermentation product under these conditions. Provision of glucose (5-30 g/L) to the fermentation medium stimulated the initial succinic acid production rate over two folds.

D-xylulose fermentation in yeasts

SummaryWith pure D-xylulose as substrate, Schizosaccharomyces pombe produced ethanol in good yield with low quantities of polyols as by-products. Saccharomyces cerevisiae was found to be a good alcohol producer in glucose but not as good in D-xylulose. Other yeast cultures converted D-xylulose to xylitol, or D-arabitol or both, with lower ethanol yield.