The use of genetically engineered microorganisms such as yeasts, algae and bacteria have the potential to produce a variety of biofuel compounds which are easier to extract since they are excreted from the microbes as is the case with ethanol. There are four different classes of compounds that are being currently developed by genetically altered microorganisms, this essay attempts to outline the main types under development as outlined by scientific literature and current company projects. The most common type of biofuel under current use is ethanol, which are one of the many types of alcohols that could be used as future biofuels. A company called Algenol has screened and altered a variety of algae that are able to excrete ethanol, as yeasts cells do. Algae have the advantage in that carbon dioxide and sunlight are used to produce biofuels. Algenol has developed a process called Direct to Ethanol which helps optimize the production of ethanol from the algae. In the future, other types of alcohols may be beneficial for biofuels, these include propanol and butanol derivates. There are a variety of metabolic pathways that have been discovered which make butanol or propanol. Pathways from the bacteria Clostridrium are known to produce good amounts of butanol. In fact, genes have been taken from Clostridrium and put into E. Coli which have produced several grams per liter of either 1-butanol, isopropanol and isobutanol [ 1. Radakovits et al 2010 ]. Algae have also been targeted genetically to produce modified alkanes or fatty acids which are excreted from the cells of algae, this allows the non-invasive extraction of biofuel related compounds.
In algae, genes that breakdown lipids can be targeted in order to produce free fatty acids, triacylglycerides (TAGs) and even alkanes. Genetic modification of these genes in algae also concentrates towards the increased excretion of these compounds from within the cells. Such work is being done by the company Synthetic Genomics. Their goal is to generate algae that can continuously excrete oil (ie fatty acids, alkanes). This production model is one of the promising ways to produce biofuels from genetically altered microorganisms since the compounds are more similar to diesel and gasoline type compounds and their extraction may be much easier since oil type compounds separate from aqueous solutions much easier than others such as alcohols. One type of algae called Botyrococcus Brauni produces very large chain hydrocarbons which may already be suitable for biofuel use. It would be interesting if genes from this algae could be transferred to other types in order to produce these large hydrocarbons. Another class of compounds receiving a great deal of attention recently is the production of isoprenoids from sources such as yeasts or genetically altered bacteria. One company called Amyris genetically engineers strains of yeasts that can produce various isoprenoids for applications related to chemical and biofuel production. Currently they have developed methods to produce an isoprenoid compound called farnesene and are planning to scale up this process for large scale production. This isoprenoid may be a type which could be used for biofuel use. E. Coli bacteria have also been targeted to host genes which can produce other types of isoprenoids such as isopentenol or pinene and terpinene which compounds have been claimed to be suitable jet fuel substitutes [ 2. Peralta-Yahya et al 2010 ]. Isoprenoid compounds are common in plants and other organisms and constitute a large set of compounds. Many of the genes which produce these biofuel type compounds have already been isolated and targeted. It is still a challenge to optimize these pathways in the correct microorganism for high yield biofuel production. However, in the short upcoming years we should be seeing the right types of host organisms with the right type of genetic and metabolic modifications for optimum biofuel production.
REFERENCES
1. "Genetic Engineering of Algae for Enhanced Biofuel Production", Eukaryotic Cell Vol 9 No 4 pgs 486-501 [2010] by R. Radakovits, RE Jinkerson, A. Darzins, M. Posewitz
2. "Advanced Biofuel Production in Microbes", Biotechnology Journal Vol 5 No 2 pgs 147-162 [2010] by PP Peralta-Yahya, JD Keasling
Photos taken from the Picassa Web Album
KEYWORDS: Ethanol from Algae, Clostridrium bacteria Butanol Production, Botyrococcus Brauni, Extracellular excreted fatty acids - lipids, Isoprenoid biofuel compounds, Genetic strains of Escheria Coli, Farnesene, Free Fatty Acids, Triacylglycerides, Propanol - Butanol alcohol derivate biofuel compounds
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