Biofuels

All our fossil fuels can be considered to be biofuels, since both methane and crude oil arise from the action of microorganisms on ancient carbon sources. However, as the cost of recovering oil and gas from underground reserves increases along with our awareness of the environmental impact of using these fuels, biofuel derived from living plant material becomes more cost-efficient. Two main approaches have been taken to biofuels: generation of biomass from sunlight for combustion and direct generation of organic solvents for use in combustion engines.

The sun provides us with more energy than we can harness, and many phototrophic organisms have been examined as possible biofuels. The idea that algal farms could be constructed that would use atmospheric carbon dioxide and sunlight to generate bio- mass seems to provide a zero carbon emission solution to energy production. Although many research groups and some start-up companies have designed realistic systems using algae or phototrophic Bacteria, a cost-effective solution has yet to be devised – it is currently cheaper to use fossil fuels. Algae do have the advantage that as well as acting as a source of combustible biomass, during phototrophic growth they  can  also produce algal oils that may act as biodiesel, or produce excess carbohydrate that can be fermented further to  produce biosolvents such as  ethanol or  butanol. Species of Botryococcus, Chlorella, and Sargassum have all been used in algal biomass pilot projects.

More controversially, waste agricultural products and even food products can be con- verted into ethanol or butanol by Bacteria. The rise in food prices in 2009 was partly attributed to the use of wheat and rice as substrates for biofuel production. Brazil has long championed the use of sugar cane as a substrate for Zymomonas mobilis, providing this fossil-fuel poor state with a ready source of ethanol for adapted automobiles. The use of bioethanol is also rising in the United States, using food-grade wheat as substrate.

Although fermentations to produce bioethanol are well understood from the long human history of brewing, ethanol is not an ideal fuel for automobiles. Longer chain alcohols such as butanol or propanol can be used more efficiently and are less prone to evaporation. However, the pathways for the production of butanol are normally found in anaero- bic Bacteria such as Clostridium acetobutyliticum, which in biotechnology are less well understood. However, recent exciting research has begun to combine the ability of some better known Bacteria to use waste products (such as corn steep liquor, olive oil waste or even potato washings) with metabolic engineering to produce E. coli that can produce butanol aerobically.