Team:Nevada/Project/Background

Consequences of our dependence on fossil fuels

The human race has become highly dependent on fossil fuels to meet its energy needs. In particular, global transportation infrastructures are built around vehicles that require petroleum derived liquid fuels. Unfortunately, because petroleum is a limiting resource and predicted to become scarce in the coming decades (Shafiee, S., and Topal, E. (2009). Policy 37, 181-189), our dependence on this resource is clearly not sustainable. The solutions to this problem are to either develop an alternative that can function as a direct replacement for petroleum as liquid fuel production or to invent modes of transportation that don’t require liquid fuel. While efforts for the latter alternative are emerging in the development of electric vehicles; efforts to address this problem in the near term will likely focus on the development of alternative liquid fuels. In addition to the economic consequences described above, the world is also experiencing drastic global climatic changes that can be traced back to our heavy consumption of fossil fuels. The increase in “greenhouse” gas emissions resulting from the combustion of fossil fuels has led to unprecedented increases in the Earth’s surface temperature (Mitchell, J.F.B. (1989).Rev Geophys 27, 115-139). Researchers forecast the occurrence of catastrophic events including rising sea levels, disease pandemics, crop failure and loss of biodiversity if these practices continue (Hughes, L. (2000) Trends in Ecology & Evolution 15, 56-61). World governments are prescribing policies to mitigate greenhouse gas emissions by curbing fossil fuel consumption. Unfortunately, without an alternative energy source such policies would cripple most industrialized nations.

Biofuels as Fossil Fuel Alternatives

The production of electricity from wind, solar, geothermal and nuclear sources will contribute greatly to replacing fossil fuels for residential and industrial energy needs. However, because we lack portable, high capacity means of storing electricity, it is currently not feasible to utilize electricity on a large enough scale to support long distance transportation systems. These systems include highly mobile forms of transport such as aircraft, automobiles, and trucks. Due to their high fuel density, liquid hydrocarbon based fuels remain the best option for these applications. Biofuels have several properties that make them ideal direct replacements to petroleum based transportation fuels. First, due to the high degree of synthetic diversity present in biology, naturally occurring or genetically engineered organisms are available that can produce chemically equivalent, or even superior compounds, as compared to current petroleum based fuels. Second, biofuels are ultimately photosynthetically derived from atmospheric carbon dioxide. As such the combustion of biofuels does not contribute to net increases in greenhouse gas levels.

Food vs. Fuel Controversy

Current first generation biofuels include biodiesel (vegetable oil) and bioethanol (fermented plant derived sugars). These fuel sources depend on available crop species which are primarily used as food sources for humans and livestock (Naylor et al. (2007)Environment 49, 30-43). For instance, corn, sugar cane and cassava, are the primary source of sugar for the fermentative production of ethanol. Biodiesel, on the other hand, is produced from edible oilseed crops including canola, soybean and palm. Using food crops as feedstocks for biofuel production is controversial because it can lead to an unbalanced situation in which the continuity of food distribution is disrupted. Early signs of such problems were seen in 2009 when ethanol subsidies by the U.S. government prompted biofuel producers to increase corn purchases (Gura (2009) Cell 138, 9-12), which lead to subsequent increases in corn prices. Corn represents a major component of livestock feed and as such a large spike in meat and dairy prices occurred (Hill et al.(2006) PNAS 103, 11206-11210; Pimentel et al. (2008) Energies 1, 41-78). The production of biofuels and biofuel fermentation feedstocks in non-food sources such as cyanobacteria and E. coli could be circumvent this problem.

Our Project

In light of the growing energy crisis, much research has been devoted to finding economical means of producing renewable fuels. Traditional methods for obtaining biofuels have relied mainly on the fermentation of agricultural crops. However, there are a number of problems with this approach: the reduction in land available for food production, relatively low levels of CO2 biofixation, and large biomass requirements. Our project aims to overcome these problems by utilizing E. coli for the production of biodiesel (C-12 fatty acids) and bioethanol. In the past there have been a number of examples of biofuel production in E. coli; however 30-40% of production cost is based on media costs (Galbe et al., 2007). Our project will surmount these high production costs by engineering the cyanobacteria, Synechocystis PCC 6803, to secrete large quantities of glucose that will feed our biofuel-producing E. coli. Cyanobacteria and E. coli will be co-cultivated in an apparatus that allows for the mutual transfer of carbon to produce biofuels. Not only will this project provide an efficient means for producing biofuels without the need for a carbon source, but it will also create a novel cooperative system between bacterial species that may have further industrial implications.

References

Galbe, M, Sassner, P, Wingren, A, & Zacchi, G. (2007). Process engineering economics of bioethanol production. 303-327.

Gura, T. (2009). Driving Biofuels from Field to Fuel Tank. Cell 138, 9-12.

Hill, J., Nelson, E., Tilman, D., Polasky, S., and Tiffany, D. (2006). Environmental, economic, and energetic costs and benefits of biodiesel and ethanol biofuels. Proceedings of the National Academy of Sciences 103, 11206-11210.

Hughes, L. (2000). Biological consequences of global warming: is the signal already apparent? Trends in Ecology & Evolution 15, 56-61.

Mitchell, J.F.B. (1989). The "Greenhouse" Effect and Climate Change. Rev Geophys 27, 115-139.

Naylor, R.L., Liska, A.J., Burke, M.B., Falcon, W.P., Gaskell, J.C., Rozelle, S.D., and

Pimentel, D., Marklein, A., Toth, M., Karpoff, M., Paul, G., McCormack, R., Kyriazis, J., and Krueger, T. (2008). Biofuel Impacts on World Food Supply: Use of Fossil Fuel, Land and Water Resources. Energies 1, 41-78.

Shafiee, S., and Topal, E. (2009). When will fossil fuel reserves be diminished? Energy Policy 37, 181-189.

Verrastro, F., and Ladislaw, S. (2007). Providing Energy Security in an Interdependent World. Washington Quarterly 30, 95-104.