Microbiology: A Systems Approach 4th Edition by Marjorie Kelly Cowan

Exercise 14

Bacteria and Biofuels
Rising oil prices and rising global temperatures have spurred entrepreneurs and scientists alike to find renewable sources of fuel that have less environmental impact. The most common types of biofuels are ethanol and biodiesel. Biodiesel can be used to power engines directly, and ethanol can be combined with gasoline to reduce carbon emissions. Ethanol is produced in the same way as the ethanol in alcoholic beverages-through fermentation of sugars and distillation. Unfortunately, the traditional methods for mass-producing ethanol from corn or other products through these methods are very expensive, giving biofuels very little advantage over crude oil in terms of cost. Another concern with using this method for biofuel production is that the corn, sugar beets, wheat, and other foods could be used for food for humans or livestock.
Scientists are now looking toward other ways to produce fuel, including using algae, and also solid biomass-the solid portion of plant products made of cellulose-that can be converted into ethanol as the source of a cheaper biofuel alternative. Solid biomass, such as wood chips, grass trimmings, or sawdust, is a waste product and is not considered competition for food production. The problem with using solid biomass is that cellulose is not easily broken down into its component sugars for fermentation. Lignin, the component of woody plants that makes them sturdy and rigid, is particularly difficult to digest.
How is glucose extracted from cellulose in plants for use in biofuel production
What organisms are involved in this process
As with any catabolic process, an enzyme is required to break lignin down into its component sugars, which then can be fermented. Several types of enzymes are involved in this process. First, the large, woody molecule lignin must be broken down into smaller pieces of cellulose. Recently, researchers at the Universities of Warwick and British Columbia discovered an enzyme capable of lignin digestion that is produced by Rhodococcus jostii , a bacterium that lives in the soil. Lignin-digesting enzymes have been identified in fungi, but bacteria are easier to grow and manipulate than fungi, making this organism an excellent source of enzymes for biofuel production. This recent research suggests that this enzyme can be used in large-scale industrial processes to produce biofuels.

Production of biofuels is not a simple process. Manufacture of ethanol from solid biomass requires many different enzymes and organisms working in concert in order to produce ethanol in a cost-effective and environmentally sound manner. Cellulase , an enzyme produced by bacteria, fungi, and protozoans, is used to break cellulose into its component sugar molecules. Saccharomyces cerevisiae , the organism traditionally used in production of beer and wine, is then used for fermenting the sugars into ethanol-based biofuels. As you see, no single organism can complete the conversion of lignin into ethanol on its own-it is truly a team effort.
What are the advantages and disadvantages of producing biofuels