Polyhydroxyalkanoate copolymers from forest biomass

• Published in: Journal of industrial microbiology & biotechnology 2006-07, Vol.33 (7), p.616-626
• Main Authors: Keenan, T.M, Nakas, J.P, Tanenbaum, S.W
• Format: Article
• Language: English
• Subjects: Activated charcoal; Alcaligenes; Alcaligenes - growth & development; Alcaligenes - metabolism; Alcaligenes eutrophus; Bacteria; Biodegradation; Biological and medical sciences; Biomass; Biorefineries; Biosynthesis; Biotechnology; Burkholderia cepacia; Burkholderia cepacia - growth & development; Burkholderia cepacia - metabolism; Calorimetry; Carbon sources; Cellulose; Charcoal; Copolymers; Detoxification; Forest biomass; Forest resources; Fundamental and applied biological sciences. Psychology; hemicellulose; hydrolysates; Industrial Microbiology - methods; levulinic acid; lignin; lignocellulose; Microbiology; Oils & fats; Polyesters - chemistry; Polyesters - metabolism; polyhydroxyalkanoate; Polyhydroxyalkanoates; Polymers; Pseudomonas putida; Pseudomonas putida - growth & development; Pseudomonas putida - metabolism; renewable energy sources; Transition temperatures; Wood - metabolism; Wood - microbiology; xylose
• ISSN: 1367-5435; 1476-5535
• DOI: 10.1007/s10295-006-0131-2

The potential for the use of woody biomass in poly-β-hydroxyalkanoate (PHA) biosynthesis is reviewed. Based on previously cited work indicating incorporation of xylose or levulinic acid (LA) into PHAs by several bacterial strains, we have initiated a study for exploring bioconversion of forest resources to technically relevant copolymers. Initially, PHA was synthesized in shake-flask cultures of Burkholderia cepacia grown on 2.2% (w/v) xylose, periodically amended with varying concentrations of levulinic acid [0.07-0.67% (w/v)]. Yields of poly(β-hydroxybutyrate-co-β-hydroxyvalerate) [P(3HB-co-3HV)] from 1.3 to 4.2 g/l were obtained and could be modulated to contain from 1.0 to 61 mol% 3-hydroxyvalerate (3HV), as determined by 1H and 13C NMR analyses. No evidence for either the 3HB or 4HV monomers was found. Characterization of these P(3HB-co-3HV) samples, which ranged in molecular mass (viscometric, M(v)) from 511-919 kDa, by differential scanning calorimetry and thermogravimetric analyses (TGA) provided data which were in agreement for previously reported P(3HB-co-3HV) copolymers. For these samples, it was noted that melting temperature (T(m)) and glass transition temperature (T(g)) decreased as a function of 3HVcontent, with T(m) demonstrating a pseudoeutectic profile as a function of mol% 3HV content. In order to extend these findings to the use of hemicellulosic process streams as an inexpensive carbon source, a detoxification procedure involving sequential overliming and activated charcoal treatments was developed. Two such detoxified process hydrolysates (NREL CF: aspen and CESF: maple) were each fermented with appropriate LA supplementation. For the NREL CF hydrolysate-based cultures amended with 0.25-0.5% LA, P(3HB-co-3HV) yields, PHA contents (PHA as percent of dry biomass), and mol% 3HV compositions of 2.0 g/l, 40% (w/w), and 16-52 mol% were obtained, respectively. Similarly, the CESF hydrolysate-based shake-flask cultures yielded 1.6 g/l PHA, 39% (w/w) PHA contents, and 4-67 mol% 3HV compositions. These data are comparable to copolymer yields and cellular contents reported for hexose plus levulinic acid-based shake-flask cultures, as reported using Alcaligenes eutrophus and Pseudomonas putida. However, our findings presage a conceivable alternative, forestry-based biorefinery approach for the production of value-added biodegradable PHA polymers. Specifically, this review describes the current and potential utilization of lignocellulosic process