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Different fungi have already been used for biomass processing with the goal of obtaining fuel. Biofuel, like ethanol, can be obtained from plants but complex cellulose molecules in plant cell walls need to be broken down into simple sugars that are then fermented into ethanol.
The very fungi that usually infect and destroy crops can be employed to make this process possible. This is so because plant pathogenic fungi have evolved to quickly and efficiently break down cell walls as they infect plants, making them an untapped resource in the search for cheap bioethanol. Hundreds of fungal species need to be screened rapidly to find the ones that can most efficiently produce biofuels. At the JGI, researchers study the fungal species Phanerochaete chrysosporium, the causal agent of white rot fungus. It us the only known microbe capable of breaking down plant lignin, one of the most abundant natural materials on Earth. P. chrysosporium is a powerful wood pulp processor.
Currently, bioethanol production is too inefficient to be cost-effective. Another problem is that most bioethanol is derived from feed corn, which has made corn more expensive due to an increase in demand. Fungal sources of ethanol will more efficiently break down nonfood plant materials, such as switchgrass and crop residues. Cellulose-degrading enzymes, or cellulases, can be extracted from four fungal species. The long-term goal is to identify enzymes that are more effective on plant material than the current industrial enzymes.
Other examples on the use of fungi for obtaining biofuels inlcude:
- Endophytes (e.g., Ascocoryne sarcoides), a class of fungi that live between plant cell walls: these fungi, in other words grow on cellulose and digest it, forming fuel-type hydrocarbons as a by-product of their metabolic processes. A compay called Sandia is developing this project.
- Persea indica: produces cineole, benzene, naphthalene and 1-methyl-1,4 cyclohexane. Cineole – also known as eucapyptol – can be used in an 8:1 blend with gasoline, while all four molecules can be used as diesel fuel additives. The ability to produce this rare compound from a fungal source “greatly expands their potential applications in medicine, industry, and energy production." This work has been published in Micobial Ecology and highlighed in a recent issue of Biorefining.
- Stereum hirsutum, Coriolus versicolor and Pleurotus ostreatus: they are used to process Eucalyptus globulus Labill wood pieces. The treatment contributes to cellulose digestibility by depolymerizing enzymes. The effect of the fungal action includes weight losses, changes in chemical composition and released sugars in the wood chips.
- Vesicular-arbuscular myc VAM interactions with the soil play an important role in controlling soil fertility, soil erosion and plant water stress. VAM fungi used in crop production should reduce fertilizer amounts applied in agriculture.
- Significance: Ethanol is an excellent transportation fuel, in some respects superior to gasoline (less pollution).... In contrast to the corn-to-ethanol conversion, the cellulose-to-ethanol route involves little or no contribution to the greenhouse effect and has a clearly positive net energy balance (five times better)... tremendous amounts of cellulose are available as municipal and industrial wastes which today contribute to our pollution problems.
- Clostridium thermocellum: thermophilic anaerobe (convenient for biotech use), can ferment cellulose to ethanol using a very efficient extracellular cellulosome enzyme complex.. “cellulolytic and ethanogenic nature, allowing saccharification and fermentation in a single step”. C. thermocellum degrades hemicellulose to xylans which can be fed to other bacteria (co-culture).
- Importance of C. thermocellum genome sequence from Raman et al. (2009)
- “Recent genome sequencing efforts have identified more than 70 dockerin-containing proteins and therefore, potentially cellulosome-related subunits encoded in the genome of C. thermocellum 27405 ([....). Genome sequence analysis has revealed the presence of several open reading frames (ORFs) encoding previously unknown proteins in C. thermocellum from different families of glycoside hydrolases, carbohydrate esterases, pectin lyases, and two serine protease inhibitors.”
- “more than 20% of these cellulosomal proteins have domains with no assigned function”
- Roberts SB (2010) Genome-scale metabolic analysis of Clostridium thermocellum for bioethanol production... “By incorporating genomic sequence data, network topology, and experimental measurements of enzyme activities and metabolite fluxes, we have generated a model that is reasonably accurate at predicting the cellular phenotype of C. thermocellum and establish a strong foundation for rational strain design. In addition, we are able to draw some important conclusions regarding the underlying metabolic mechanisms for observed behaviors of C. thermocellum and highlight remaining gaps in the existing genome annotations.”
Algae are important alternative sources of oil. Algae are one of the fastest growing and most adaptive organisms on the planet. The hope is to learn how to capture CO2 from the atmosphere and to output fuels that can meet our energy needs.
The extraction of the oil from algae involves algal harvesting, lipids (oils) extraction from the walls of the algae cells. The oil press is the simplest, most popular method because it extracts up to 75% of the oil from the algae being pressed.
Another process is called the hexane solvent method. In this method, the hexane solvent is combined with combined with the pressed algae, which then extracts up to 95% of oil from algae. First, the press squeezes the oil. Then, the leftover algae is mixed with hexane, filtered, and cleaned so as to ensure that no chemical is left in the oil.
A third process is known as the supercritical fluids method. This method extracts up to 100% of the oil from algae. Carbon dioxide behaves as the supercritical fluid—when a substance is pressurized and heated to change its composition into a liquid as well as a gas. The carbon dioxide is then mixed with the algae. Once combined, the carbon dioxide turns the algae into oil. The additional equipment and work needed in this method makes it a less popular option.
Once the oil has been extracted from the algae cells, it is refined using fatty acid chains in a process called transesterification. In this process, a catalyst such as sodium hydroxide is mixed in with an alcohol such as methanol. This creates a biodiesel fuel combined with glycerol. The mixture is then refined to remove the glycerol, leaving the final product: algae biodiesel fuel.
Switchgrass is used to extract fast growing biomass from which ethanol and other fuels can be extracted.