Feasibility analysis of Poly-β-Hydroxybutyrate (PHB) extraction from hybrid poplar leaves

Poly-β-Hydroxybutyrate (PHB) is a biopolymer that shows great promise to replace olefin based polymers. PHB is naturally produced by several species of bacteria and has demonstrated biodegradability unlike polymers derived from petrochemicals. Higher plants such as sugarcane and alfalfa have been engineered to express bacterial PHB genes, thus adding the additional benefit of carbon sequestration to the PHB production process. Hybrid poplar trees provide one example of a renewable plant source of this polymer. Recently, PHB producing genes have been expressed in hybrid poplar trees and PHB accumulation in leaves has been demonstrated. However, the use of plants adds new technical challenges related to the extraction and consolidation of the PHB product contained within the resilient plant cells. A modified chloroform extraction was developed to quantify and extract PHB from poplar leaves. PHB content of hybrid of poplars was determined to be 0.763±0.076 % (w/w). Composition analysis indicated that total ash, nitrogen and carbon contents were 8.43±0.13, 2.68±0.15 and 42.9±3.04 respectively. Cost of PHB production was dependent on PHB content of leaves and varied from $33.56/Kg to $2.96/Kg for PHB content of 1.0 to 12.5% (W/W). Economic viability of PHB production in poplars is possible for PHB content of >12.5 % (w/w) using chloroform extraction processes. Reducing the overhead costs and increasing the PHB content of poplar leaves to >12.5% (w/w) could make PHB economically competitive against petroleum based polymers such as polypropylene.