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From biomass to renewable chemicals: while industrial biotechnology offers a clear value proposition, a number of hurdles need to be addressed to fully realize the commercial potential of bio-based products and chemicals over the coming decade. A review of an early roadmap for biological production of chemicals from renewable sugars reveals a focus on those that would provide co-products for integrated biorefineries producing biofuels and bioenergy. A growing number of companies are now focusing on specialty chemicals as an entry point to build the bio-based economy. BDO, 1, 4 butanediol; DOE, Department of Energy; PDO, 1,3 propanediol; PHA, polyhydroxyalkanoate; PLA, polylactic acid; RFS, Renewable Fuel Standard Industrial biotechnology encompasses the application of biotechnology-based tools to traditional industrial processes (“bioprocessing”) and the manufacturing of bio-based products (such as fuels, chemicals and plastics) from renewable feedstocks. Microbes, microorganisms, enzymes and their genetic engineering form the basis of a suite of technologies and processes that a diverse group of companies, researchers and scientists are seeking to develop for commercial use. Mankind has been using microbial processes for producing foods and other goods since Neolithic times. But the evolution of our ability to manipulate microbial genomes has revolutionized the field of biotechnology and produced a rapid increase in innovation for industrial uses. In most cases, industrial biotech tools allow industry to develop new industrial manufacturing processes that are cleaner and better for the environment with reduced economic costs. Industrial biotech represents the third wave in biotechnology, following innovation in the health care and agricultural sectors. While biofuels have attracted a great deal of interest among the public, press and policy makers, renewable chemicals represent another major opportunity to commercialize industrial biotechnology in existing markets, at lower capital costs, and with potentially higher returns. Early efforts to lay a roadmap for biological production of chemicals from renewable sugars focused on those that would provide co-products for integrated biorefineries producing biofuels and bioenergy as the primary product. A growing number of companies are now focusing on specialty chemicals as an entry point to build the bio-based economy. Currently there are many examples of microbial processes and renewable agricultural materials used in producing material goods, including cheese making and other fermentations. But an increased understanding of, and ability to restructure, fermentation processes and microbial metabolic systems has allowed researchers to expand the application and engineering of microbes and enzymes into a broader variety of industrial processes. These processes can often construct products faster and in a resource- and environmentally sustainable manner at reduced cost, while using less energy 1. Further, industrial biotechnology can reduce carbon emissions through improved process efficiency, the displacement of fossil fuels and petroleum-based materials, and the creation of closed loop industrial systems that eliminate waste 2. Industrial biotechnology's enabling of integrated biorefineries that produce multiple product and value streams is viewed as potentially transforming the economics of industrial production 3. New techniques, such as synthetic biology, can potentially speedup the development and commercialization of industrial biotech processes, making them attractive and affordable to manufacturers. Living systems manage their chemistry more efficiently than man-made chemical refineries, and most of the wastes they generate are recyclable or biodegradable. Nature's enzyme-based processes operate at lower temperatures, and produce less toxic waste and fewer emissions than conventional chemical processes. Because enzymes have precise chemical selectivity, they may also use less purified raw materials. These characteristics can be exploited to increase the energy efficiency and improve the environmental profile of chemical reactions used in manufacturing 1. Industrial biotechnology companies use life-science techniques to find and improve nature's enzymes or develop diverse microbial systems – from bacteria, yeasts, and fungi to marine diatoms and protozoa – for use in industrial applications. Companies search for enzyme-producing microorganisms in the natural environment (bioprospecting) and then use genomic and proteomic studies and tools to fish for genes that express enzymes with specific biocatalytic capabilities. Once identified, enzymes can be characterized for their ability to function in specific industrial processes. If necessary, enzymes can be improved with biotechnology techniques, such as gene transfer, gene shuffling, directed evolution or metabolic engineering. Once useful enzymes are discovered and improved, they can be produced in commercial quantities using either naturally occurring or genetically enhanced microbes (GEMs). Currently, it is common for genetically engineered microbes (for example, bacteria or yeast improved through gene shuffling) to carry out the fermentation. Fermentation and reproduction of the organism are normally done in contained stainless steel fermentation tanks or systems similar to those that produce human therapeutic proteins or bulk yeast for the brewing industry. Biotechnology enables scientists to maximize the effectiveness and efficiency of enzymes and microbes or to custom tailor the specificity of enzymes, improve catalytic properties or broaden the conditions under which enzymes can function so that they are more compatible with existing industrial processes. Scientists can also give new manufacturing capabilities to these microscopic workhorses by genetically enhancing them so they make enzymes that would otherwise have to be produced by microorganisms that are expensive or too finicky to cultivate in industrial quantities. With libraries of bioinformatic material that can be replicated or chemically reconstructed, researchers and companies are beginning to design and create novel microbial systems that perform multistep processes to metabolize renewable sugars into chemical building blocks, monomers, polymers and acids. Synthetic biology has also enabled the creation of novel enzymes that can work in multi-step biocatalysis of chemicals, such as for pharmaceuticals (see for instance http://www.epa.gov/gcc/pubs/pgcc/winners/grca10.html). The reconstruction of DNA strands from their chemical base elements according to computer-aided designs for metabolic platforms has given rise to the term “synthetic biology.” Many, but not all, industrial biotechnology applications involve the harnessing of nature's enzymes. Industrial biotechnology can use extracted enzymes or whole cell systems to accomplish a task. The recent and dramatic advances in biotechnology techniques are why so many biocatalytic tools are becoming available to be used in industrial applications. Biorefineries are dedicated facilities that convert the sugars, oils and proteins derived from renewable biomass into biofuels, chemicals and materials such as plastics and polymers. The concept is modeled on the petroleum refinery, in which crude oil is converted into fuels and chemicals that provide multiple product and revenue streams. Just as a barrel of oil can be broken down into constituent parts that add up to more by volume and value than the original barrel, the objective of a biorefinery is to develop as many product and value streams as possible from biomass. This optimization and efficiency are essential for economic and environmental sustainability. There are many existing biorefineries in the United States that process corn into sugars (such as high fructose corn syrup), oils, animal feeds and food ingredients (such as xanthan gum). More than 200 ethanol biorefineries have been built, primarily using the corn's starch for biofuel and the remaining protein and fat for animal feed and vegetable oils. Some of these first-generation biorefineries are looking to create product and value streams from the cellulosic bran in the kernel and the stover (leaves and stalks) of the corn plant for additional product and value streams. There has been rapid growth in construction of corn ethanol biorefineries since 2005, when the Renewable Fuel Standard (RFS) was first enacted, due to the economic opportunity presented by high oil prices and the phase out of methyl tertiary butyl ether (MTBE) in gasoline 4. Figure 1 details this growth. The RFS was enacted in the United States in recognition of the national security implications of overreliance on foreign supplies of petroleum, the energy security implications of oil's price volatility, and the ongoing environmental costs of fossil fuel use. Corn ethanol biorefineries that coproduce animal feed (distillers grains, corn gluten meal and corn gluten feed) and corn oil have very simple economic models that displace some use of petroleum for fuel and feed. Much more sustainable models that fractionate the corn kernel for additional value streams are now being developed, and use of renewable energy sources for power and electricity generation are in development. Petroleum's price volatility affects the entire value chain for petroleum refineries, pushing industry to seek replacements for the “entire barrel of oil.” Growth of corn ethanol refining, 2000–2011. Construction of new ethanol biorefineries and expansion of existing production capacity accelerated following the adoption of the nation's first RFS in 2005. There are a growing number of demonstration and pilot-scale biorefineries across North America that plan to use locally produced biomass, including starches such as sorghum; cellulosic feedstocks such as grasses, woody biomass (fast-growing trees and shrubs or forestry residues); municipal solid waste; and algae. Cellulosic biomass is the most abundant source of carbon, and its ubiquity makes it potentially the lowest-cost source of renewable sugars for biorefineries. A great deal of industrial biotech research and development has focused on enzymatic conversion of cellulose to sugars and consolidated metabolic bioprocessing of cellulose to higher value molecules. The challenge for any biorefinery is to establish a reliable supply chain for sufficient feedstock at a stable price. In the United States, there are well-established supply chains for pricing and delivery of corn. Collection, harvesting, storage and transport of other biomass feedstocks – including corn stover – are in development, but rely to a large degree on expectations that market demand among biorefineries will exist. Biotechnology is playing an important role in increasing productivity for many biomass feedstocks, utilizing the same tools that have enabled increased production of corn and soy, namely pesticide and herbicide resistance. Genetic engineering tools applied to commercial production of microbes are being applied to algae – including gene shuffling, gene transfer, and even synthetic biology – to increase the productivity of target strains. Biorefineries are expected to follow common business imperatives of industrial ecology. To remain economically competitive, they must continually innovate, increase efficiency, and develop new product and value streams. Biorefineries must seek to maximize the use of biomass, recycle waste streams as input for new product streams, and utilize heat from primary processes as energy for secondary processes. Biotech routes to a wide array of chemical products are being developed for integration into biorefineries, allowing for diversification of product and value streams. In 2004, the U.S. Department of Energy (DOE) conducted an initial screening and categorization of renewable chemicals that could be co-produced as side streams of biofuels and bioenergy 5. The analysis yielded a list of 30 potential monomers with up to six carbon atoms that could be fermented from the sugars in biomass and serve as building blocks for more complex chemicals – as intermediates, novel or replacements for petroleum of these chemicals, in 1, as for research and development industrial The that its of biorefinery products was to the with to six carbon chains derived from the sugars in biomass. 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Erickson et al. (Tue,) studied this question.