PHA bioplastic: A value‐added coproduct for biomass biorefineries

Abstract

The petroleum industry has optimized profi ts by producing value-added coproducts, such as plastics and chemicals, in addition to primary liquid fuels. A similar coproduct strategy applied to biorefi neries processing cellulosic biomass to liquid fuels and/or energy would transform a technology that is marginally economic, depending on oil prices, to a sustainable business with enhanced revenue streams from multiple coproducts. The challenge is fi nding a biobased coproduct that is compatible with a biorefi nery scenario and where markets warrant its production on a similar scale as liquid fuels and/or energy. Polyhydroxyalkanoate (PHA) bioplastics represent a coproduct that would be entirely compatible with either production of liquid fuels by hydrolyzing the residual biomass after PHA extraction or by alternative thermochemical processes. PHA bioplastics possess properties making them suitable replacements for many of the applications currently served by petroleum-based plastics, thus providing tremendous market potential. Proof-of-concept technology for production of these plastics in several crops of agronomic interest has been demonstrated. In this review, we show that the potential for developing biomass-based biorefi neries producing liquid fuels and a value-added coproduct is both real and realizable. Examples using switchgrass producing PHA bioplastics as a coproduct are described.

High Levels of Bioplastic Are Produced in Fertile Transplastomic Tobacco Plants Engineered with a Synthetic Operon for the Production of Polyhydroxybutyrate

“…Significant progress has been made in efforts to produce PHAs in microbial systems using large-scale industrial fermentations of bacteria, and select compositions of materials produced using this technology are in commercial production (Snell and Peoples, 2009;Coons, 2010). Direct production of PHAs in crop plants is another route for large-scale manufacture of these polymers and could be especially advantageous in energy crops, where a plant byproduct, such as biomass or seed oil, could be used for the production of energy (Snell and Peoples, 2009).…”

“…Significant progress has been made in efforts to produce PHAs in microbial systems using large-scale industrial fermentations of bacteria, and select compositions of materials produced using this technology are in commercial production (Snell and Peoples, 2009;Coons, 2010). Direct production of PHAs in crop plants is another route for large-scale manufacture of these polymers and could be especially advantageous in energy crops, where a plant byproduct, such as biomass or seed oil, could be used for the production of energy (Snell and Peoples, 2009). Most of the efforts to produce PHAs in plants have focused on the homopolymer PHB or the copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate, although some effort has been directed toward the production of medium-chain-length PHAs (Suriyamongkol et al, 2007;van Beilen and Poirier, 2008;Snell and Peoples, 2009).…”

“…Direct production of PHAs in crop plants is another route for large-scale manufacture of these polymers and could be especially advantageous in energy crops, where a plant byproduct, such as biomass or seed oil, could be used for the production of energy (Snell and Peoples, 2009). Most of the efforts to produce PHAs in plants have focused on the homopolymer PHB or the copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate, although some effort has been directed toward the production of medium-chain-length PHAs (Suriyamongkol et al, 2007;van Beilen and Poirier, 2008;Snell and Peoples, 2009). To date, the highest levels of PHB have been achieved in plastids (Suriyamongkol et al, 2007;van Beilen and Poirier, 2008;Snell and Peoples, 2009), likely due to the high flux of the PHB pathway substrate acetyl-CoA through this organelle during fatty acid biosynthesis.…”

“…Most of the efforts to produce PHAs in plants have focused on the homopolymer PHB or the copolymer poly-3-hydroxybutyrate-co-3-hydroxyvalerate, although some effort has been directed toward the production of medium-chain-length PHAs (Suriyamongkol et al, 2007;van Beilen and Poirier, 2008;Snell and Peoples, 2009). To date, the highest levels of PHB have been achieved in plastids (Suriyamongkol et al, 2007;van Beilen and Poirier, 2008;Snell and Peoples, 2009), likely due to the high flux of the PHB pathway substrate acetyl-CoA through this organelle during fatty acid biosynthesis. In the model plant Arabidopsis (Arabidopsis thaliana), PHB has been produced in leaf tissue samples at levels up to 4% of the tissue's fresh weight (equivalent to approximately 40% dry weight PHB) in plants engineered with nucleus-encoded expression cassettes for plastid-targeted enzymes (Bohmert et al, 2000).…”

“…In the model plant Arabidopsis (Arabidopsis thaliana), PHB has been produced in leaf tissue samples at levels up to 4% of the tissue's fresh weight (equivalent to approximately 40% dry weight PHB) in plants engineered with nucleus-encoded expression cassettes for plastid-targeted enzymes (Bohmert et al, 2000). In other plants, PHB levels ranging from trace amounts to 7.7% of the dry weight of the leaf or seed sample have been achieved depending on the plant host (Poirier and Gruys, 2002;Suriyamongkol et al, 2007;Snell and Peoples, 2009). PHB synthesis in biomass crops of industrial interest such as switchgrass (Panicum virgatum; Somleva et al, 2008), sugarcane (Saccharum spp.…”