Microbial Production of Ethanol

Raw materials for the fermentation of ethanol are sugar molasses (Brazil), com steep liquor and corn starch hydrolysate (USA). Industrial ethanol fermentation is highly developed and the stoichiometric yield can be as high as 1.9 mol mol-1 [25, 26]. The 

STY is high for a fermentative procedure and ranges from 140 g L-1 d 1 for a continuous tank reactor to 1.2 kg IT1 d 1 in a continuous tower reactor with cell recycle. Depending on the ethanol tolerance of the production species, ethanol is produced to a concentration of 12-20%. The ethanol is traditionally recovered from the fermentation broth via an energy-intensive distillation step, but it is sought to replace the latter by pervaporation or reversed osmosis [25]. 

This intractable problem may now be close to being solved. A Saccharomyces species that expressed the xylose isomerase gene from an anaerobic fungus was found to grow slowly on pentoses [29]. Improvement resulted from a combination of rational engineering - overexpression of the pentose phosphate-converting enzymes (see Fig. 8.5) - and classical strain improvement [30]. The authors conclude The kinetics of xylose fermentation are no longer a bottleneck in the industrial production of ethanol with yeast  

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Owing to diminishing fossil fuel reserves, alternative energy sources need to be renewable, sustainable, efficient, cost-effective, convenient and safe.1 In recent decades, microbial production of ethanol has been considered as an alternative fuel for the future because fossil fuels are depleting. Several microorganisms, including Clostridium sp. and yeast, the well-known ethanol producers Saccharomyces cerevisiae and Zymomonas mobilis, are suitable candidates to produce ethanol.2,3... 

Use of biofilm reactors for ethanol production has been investigated to improve the economics and performance of fermentation processes.8 Immobilisation of microbial cells for fermentation has been developed to eliminate inhibition caused by high concentrations of substrate and product, also to enhance productivity and yield of ethanol. Recent work on ethanol production in an immobilised cell reactor (ICR) showed that production of ethanol using Zymomonas mobilis was doubled.9 The immobilised recombinant Z. mobilis was also successfully used with high concentrations of sugar (12%-15%).10... 

Samejima, H., Nagashima, M., Azuma, M., Noguchi, S., and Inuzuka, K., Semicommercial Production of Ethanol using Immobilized Microbial Cells, Annals New York Academy of Sciences, 434 394 (1984)... 

Similarly, catechin polymers formed upon horseradish peroxidase-catalyzed oxidation of catechin or polycondensation of catechin with aldehydes prove much more efficient than catechin (at identical monomer concentration) at inhibiting XO and superoxide formation. A more detailed investigation with the catechin-acetaldehyde polycondensate (which is expected to form in wine because of the microbial oxidation of ethanol to acetaldehyde) shows that inhibition is noncompetitive to xanthine and likely occurs via binding to the FAD or Fe/S redox centers involved in electron transfers from the reduced molybdenum center to dioxygen with simultaneous production of superoxide. 

Some yeasts and bacteria are able to produce different alcohols like ethanol and butanol as well as polyols like glycerin and 2,3-butandiol. These compounds- are used in drinks such as beer and wines, and also may be used in or as solvents, drugs, chemicals, oils, waxes, lacquers, antifreezing and antifoaming agents, precipitants, dyestuff, pomades, raw materials for chemical syntheses, motor fuels, and carbon sources for SCP production. These products are mainly synthesized from petroleum — derived materials like ethylene and acetaldehyde. However, because of the insufficient availability and high prices of the raw materials, the microbial production of alcohols has become an interesting area for many researchers. 

The incorporation of acetaldehyde derived bridges between anthocyanins and flavan-3-ols via acetaldehyde condensation reactions has been well described in fermented beverages such as red wine. The presence of acetaldehyde in alcoholic solutions is attributed to either oxidatative products of ethanol or microbial byproducts. In the case of cranbeny fruit and spray dried juice neither product was subjected to yeast fermentation. It becomes a concern then that die observed anthocyanin-pigments may be an arti ct of harvest, storage, juice processing or analytic techniques. 

A total of almost 250 ISPR projects in microbial whole cell biotechnology are listed in Table 2. Over one third of these projects have dealt with the production of organic solvents such as ethanol, butanol, acetone or propanol (90 projects). Ethanol (70% of all the solvents) has been by far the most important microbial product for which different ISPR techniques have been applied. The second most important class of products involved in ISPR projects have been organic acids such as lactic, acetic, butyric, or propionic acid (54 projects). Most of effort in this product class has focused on lactic acid (55% of all organic acids). Important ISPR activities have also been reported for the microbial production of various aromas and fine chemicals (30 projects in each product category). A considerable amount of ISPR approaches have been shown in steroid conversions (17 projects) and the production of secondary metaboHtes and various enzymes (13 projects in each product category). 

The production of ethanol alone is not economically feasible without continued subsidies but a plant becomes profitable if it produces ethanol and furfural as co-products (10). The technology development in the Latvian State Institute of Wood Chemistry (LSIWC) provides an excellent possibility for producing both furfural and ethanol. As a result, the problem of the complete utilization of the deciduous wood polysaccharide complex yielding furfural and fermentable sugars to be used subsequently for the production of bioethanol and other microbial synthesis products has been solved. Residual lignin could be used as a calorific fuel. 

Starch materials. These are the most important raw materials which can be used for production of ethanol by microbial strains. Sweet potato, cassava, maize, potato, barley, rice, and sorghum all belong to starch materials. 

The bioconversion of cellulose into ethanol with conventional methods is usually achieved in two steps first being the enzymatic saccharification of the polysaccharide to monosaccharide and secondly the bioconversion of monosaccharides into ethanol. A combination of enzymatic hydrolysis and ethanol production in the same reactor has been attempted using different cellulases and ethanol producing microbial species to improve process efficiency [46-53]. The production of ethanol from cellulose in a simultaneous saccharification and biological conversion process alleviates the problem of end product inhibition, since glucose does not accumulate in this system and is converted to ethanol immediately following saccharification [46]. 

Trinh CT, Carlson R, Wlaschin A, Srienc E (2006) Design, construction and performance of the most efficient biomass producing E. coli bacterium. Metab Eng 8 628-638 Trinh CT, Unrean P, Srienc E (2008) Minimal Escherichia coli ceU for the most efficient production of ethanol from hexoses and pentoses. Appl Environ Microbiol 74 3634—3643 Trinh CT, Wlaschin A, Srienc E (2009) Elementary mode aneilysis a useful metabohc pathway analysis tool for characterizing cellular metabolism. Appl Microbiol Biotechnol 81 813—826 Van Der Meet MTJ, Schouten S, Bateson MM, Niibel U, Wieland A, KiiM M, De Leeuw JW, Damste JSS, Ward DM (2005) Diel variations in carbon metabolism by green nonsulfur-Hke bacteria in alkaline siliceous hot spring microbial mats from Yellowstone national park. Appl Environ Microbiol 71 3978-3986... 

One goal of the metabolic engineering work described here is the development of microbial biocatalysts with improved production of ethanol from the desired substrate. A second goal, with varying degree of emphasis, is to learn why certain strategies or manipulations were successful (or not). This sort of analysis is especially important when attempting to extrapolate results from ethanol production to other biorenewable fuels and chemicals. 

A two-step microbial process yields a dilute 5-12 % solution of acetic acid (vinegar) from a crude carbohydrate-containing mash. The first step is the production of ethanol fi om sugars by an anaerobic fermentation, usually by the yeast Saccharomyces cerevisiae or alternatively by a bacterium such as Zymomonas mobilis... 

The early development of microbial processes for industrial production of ethanol or lactic acid occurred in Berfin at the Research Institute for Fermentation Industries, directed by Max Delbrfick. The major accomplishments of this institution were the preparation of pure cultures of bacteria or yeasts for industrial fermentations and the application of the principle of natural pure culturing. In natural pure culturing, the... 

The study of microbial production of 1,3-propanediol has an interesting history (reviewed by Biebl et al. 1999). It is one of the oldest fermentation products known and has been studied for over 100 years. For a number of years, interest in the fermentation was due to its potential as an outlet for surplus glycerol. Glycerol can be made via a chemical process, or it can be derived from various agricultural fats during the production of fatty acids and soaps. Increased availability of low-cost glycerol might be expected in the future, as it is a by-product of such processes as transesterification of fats for biodiesel production as well as the process for ethanol production by yeast. 

The industrial focus on 1,3-propanediol has sparked interest in the microbial production of 1,2-propanediol. Some work has focused on the fermentation process of 1,2-propanediol as well as the metabolic engineering of pathways for its production. In early work with C. thermosaccharolyticum, various process conditions were examined such as temperature, pH, gas phase composition, and substrate concentration. This work was conducted in a volume of 2 1. The maximum cell concentration achieved was in the range of 1.0-1.3 g/1. The temperature range examined was 50-65 °C, and the optimal temperature for production was 60 °C. At higher temperatures, lactate decreased and ethanol increased. The pH range studied was from 6.0 to 7.2. At the optimal pH of 6.0, a concentration of 5.6 g/1 of 1,2-PD was obtained. Other fermentation conditions were examined such as... 

Taherzadeh MJ, Karimi K (2008) Pretreatment of lignocellulosic wastes to improve ethanol and biogas production a review. Int J Mol Sci 9 1621—1651. doi 10.3390/ijms9091621 Tsuge T (2002) Metabolic improvements and use of inexpensive carbrni sources in microbial production of polyhydroxyalkanoates. J Biosci Bioeng 94(6) 579-584. doi 10.1016/S1389-1723(02)80198-0... 

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