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How to accelerate cellulosic biofuel production?
Plants could be useful source of biofuel. Ethanol can be derived from lignocelluloses (structural element of the cell wall in plants), from inedible part of the plants, wood or grass. Cellulosic ethanol undergoes longer processing than starch ethanol derived from corn or cane sugar. Advantage of this type of biofuel is mainly in the availability of biomass used and its type; plants used for cellulosic ethanol production are more diverse and have greater productivity compared to ones used in conventional biofuel production. Switchgrass (Panicum virgatum) and Miscanthus (Miscanthus x giganteus) are mostly used due to high productivity rate. Also, cellulosic ethanol decreases green house emission by 85% compared to reformulated gasoline and it is more eco-friendly than starch ethanol (doesn’t affect green house emission at all).

Main obstacle in cellulosic ethanol production lays in complicated extraction procedure. Two mechanisms are applied today: enzymatically triggered cellulolysis (by degrading the cellulose to glucose that will be fermented to ethanol later) and gasification (converting the lignocellulose to carbon monoxide and hydrogen that will be transformed to ethanol via fermentation or chemical catalysis). Due to large size and rigid structure, biomass used for cellulosic ethanol production needs to be processed physically first. This procedure will reduce biomass size. Lignin and cellulose are tightly bound with one another and chemical pretreatment that will release cellulose is essential to provide successful hydrolysis and further processing. By removing chemical barrier, enzymes could digest cellulose maximally and this process is called cellulose liberalization. Hydrolysis can be achieved chemically (using acids) or enzymatically (usually fungi derived enzymes). Enzymes used in hydrolysis have been improved over the years and some companies are developing genetically modified fungi producing enzymes such as cellulose, hemicellulase, and xylanase. Saccharomyces cerevisiae (baking yeast) is mostly used in brewery industry for sugar fermentation. Yeast is often and widely used microorganism that could survive harsh environmental conditions (bacterial metabolites, low pH, and high ethanol level for example). Genetically improved, it can produce ethanol from xylose and arabinose (or from both sugars). Beside yeast, Escherichia coli and Zymomonas mobilis will probably be genetically modified to enhance their fermentation potential for future biofuel productions.

Cellulosic ethanol production could be accelerated thanks to group of scientists and their recent discoveries. Scientists wanted to explore complex structure of the cell and its structural element, and reveal weak points in the currently used method of cellulose ethanol production and finally eliminate them. Using special imagining techniques, cellular architecture was examined on the nanoscale. Enzymes are one of the most important factors in successful ethanol production as they degrade biomass and speed up chemical reactions. This study especially focused on the currently used enzymes to investigate their mechanisms of action and assess potential weak points. Fungus and bacterium derived enzymes were used for evaluation of the cell wall degradation and sugar intermediate production. Exact location of enzymes responsible for degradation and exact digestion spots were discovered. Bacterial enzymes used are organized in large scaffolds prior attacking the cell wall, while fungi derived enzymes attack cellular wall individually. In both approaches, non-sugar particle (lignin) prevents the enzyme from reaching the target (cellulose). Pretreatment that could remove lignin without disturbing established cellular structure would be the optimal for cellulosic ethanol production. Scientists compared the model with large house that needs to be remodeled. If all doors in the house would be removed or left open, workers would be able to reach each room (and desired wall) easily, without wasting time. That approach is opposite to currently used pretreatment method where all spongier carbohydrates are usually removed, resulting in the structure that could easily lose its stability and collapse. When cellular structure is disrupted, resulted half “demolished house” couldn't be easily approached or remodeled. Enzymes work perfectly if they are dealing with structures in their natural environment. By removing unwanted materials from the cellular wall (lignin) without disturbing its biochemical properties and main “skeleton”, enzymes would have optimal working surface and speed of work would be sufficiently increased.

This discovery could optimize biofuel production by changing the direction of the future experiments and operating procedures. Further experiments and even deeper analysis of cellular dynamic and structure will provide more valuable information that could be beneficial for the cellulosic ethanol production.
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