Biomass, which constitutes a significant portion of municipal and industrial solid waste, refers to organic plant material that can be used as fuel or, more importantly, to produce fuel. Through photosynthesis, energy from the sun is stored in the chemical bonds of the plant material. It is this energy that is harnessed in biomass.
Examples of biomass include agricultural residues such as corn husks/stalks, sugar cane fiber, rice chaff, and wood waste including paper trash, yard clippings, saw dust, and wood chips. It is the sugar content of biomass that makes it particularly useful for fuel ethanol production.
Biotechnological methods such as genetic engineering can be used to transform microorganisms to convert the sugars in biomass into ethanol. It has been estimated that microbial conversion of the sugar residues present in waste paper and yard trash from U.S. landfills could provide over 10 billion gallons of ethanol. Such cellulosic ethanol would require less energy and would be produced from waste material that is otherwise buried or burned. More importantly, corn currently used to produce ethanol could be better used to feed livestock and people.
Recombinant DNA technology could transform the ethanol industry. But, is the current geopolitical situation the mother of invention? Not necessarily, because this technology has been around for a while.
For example, U.S patent 5,000,000, granted in 1991, describes ethanol production by E. coli strains engineered to express heterologous pyruvate decarboxylase (pdc) and alcohol dehydrogenase (adh) of Zymomonas mobilis. E. coli, a gram-negative enteric bacterium, is not naturally ethanologenic. That is, it does not produce ethanol as a major metabolic by-product but rather produces organic acids such as lactate, acetate, succinate, and butyrate as major metabolic by-products. E. coli is a robust organism and can break down a variety of organic materials, including cellulose, which is why it is the predominant normal flora found in the human digestive system.
Z. mobilis, commonly found in plant saps and honey, has unusual metabolic characteristics and is reportedly capable of producing ethanol at rates that are substantially higher than that of yeasts. However, the range of sugars metabolized by this organism is limited and normally consists of glucose, fructose, and sucrose.
Co-expression of pdc and adh genes of Z. mobilis by recombinant E. coli enables the organism to ferment a wide variety of sugars resulting from breakdown of cellulose into ethanol. By means of genetic engineering, E. coli can produce ethanol as a primary fermentation product.
However, the sugars present in the majority of the world’s cheap, renewable sources of biomass are not solely simple monomeric sugars such as glucose but include more complex sugars such as xylose, the primary sugar component, as well as arabinose, mannose, and galactose. Thus, the technology has been extended to other gram-negative enteric bacteria such as Klebsiella and Erwinia (see, e.g., U.S. patent 5,424,202, issued in 1995), which co-express not only ethanol production genes but also genes coding for proteins that enable the host to transport and metabolize oligosaccharides and polysaccharase genes coding for proteins that degrade the feedstock into fermentable monosaccharides and oligosaccharides.
Likewise, the technology has been extended to gram-positive bacteria including Bacillus, Lactobacillus, Streptococcus, Fibribacter, Ruminococcus, Pediococcus, Cytophaga, Cellulomonas, Bacteroides, and Clostridium.
In the wake of the war in Iraq, the U.S. government has significantly stepped up funding for research in renewable energy sources, including ethanol production from biomass. Similarly, the venture and corporate communities have realized the potential for growth and return on investment in this industry sector and have begun making significant and meaningful investments.
Future R&D will focus on making ethanol production from biomass cost-competitive with gasoline production through improvements in recombinant microorganisms and refinements in the preparation and handling of feedstocks and the saccharification and fermentation process. Future IP will reside in these improvements and refinements.
Clearly this biotechnology application has the potential to revolutionize solid-waste management by making biomass the black gold or Texas tea of the 21st century the way that crude oil was in the 20th century. As exciting as the future possibilities are, just imagine if we had the political will to exploit fully this technology back in 1991, when U.S. patent 5,000,000 was granted. Perhaps we would not be involved in a war in Iraq.