title: One-pot microbial production, mechanical properties, and enzymatic degradation of isotactic P[(R)-2-hydroxybutyrate] and its copolymer with (R)-lactate.
abstract: P[(R)-2-hydroxybutyrate] [P((R)-2HB)] is an aliphatic polyester analogous to poly(lactic acid) (PLA). However, little has been known for its properties because of a high cost of commercially available chiral 2HB as a starting substance for chemical polymer synthesis. In this study, P[(R)-2HB] and P[(R)-2HB-co-(R)-lactate] [P((R)-2HB-co-(R)-LA)] with a new monomer combination were successfully synthesized in recombinant Escherichia coli LS5218 from less-expensive racemic 2HB using an R-specific polyester synthase. The cells expressing an engineered polyhydroxyalkanoate synthase from Pseudomonas sp. 61-3 and propionyl-CoA transferase from Megasphaera elsdenii were grown on LB medium containing 2HB and glucose in a shake flask and accumulated up to 17 wt % of P[(R)-2HB] with optical purity of >99.1%. In addition, the same cells cultured in a jar-fermentor produced P(86 mol % 2HB-co-LA) copolymer. Notably, the molecular weights (Mw) of P(2HB) (27000) and P(2HB-co-LA) (39000) were 2- and 3-fold higher than that of P(2HB) previously synthesized by chemical polycondensation. P(2HB) was processed into a transparent film by solvent-casting and it had flexible properties with elongation at break of 173%, which was contrast to the rigid PLA. Regarding mechanical properties, P(2HB-co-LA) was tougher but less stretchy than P(2HB). These results demonstrated that P(2HB) has useful properties and LA units in 2HB-based polymers can act as a controllable modulator of the material properties. In addition, P[(R)-2HB] was efficiently degraded by treatment of Novozym 42044 (lipase) but not Savinase 16L (protease), indicating that the degrading behavior of the polymer was similar to that of P[(R)-LA].
authors.affiliation: Division of Biotechnology and Macromolecular Chemistry, Graduate School of Engineering, Hokkaido University , N13W8, Kitaku, Sapporo, 060-8628, Japan. mken@eng.hokudai.ac.jp
authors.forename: Ken'ichiro
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Satsuki
authors.initials: S
authors.lastname: Terai
authors.forename: Ayako
authors.initials: A
authors.lastname: Ishiyama
authors.forename: Jian
authors.initials: J
authors.lastname: Sun
authors.forename: Taizo
authors.initials: T
authors.lastname: Kabe
authors.forename: Yuyang
authors.initials: Y
authors.lastname: Song
authors.forename: John Masani
authors.initials: JM
authors.lastname: Nduko
authors.forename: Tadahisa
authors.initials: T
authors.lastname: Iwata
authors.forename: Seiichi
authors.initials: S
authors.lastname: Taguchi
mesh_terms: D019149:Bioreactors; D002851:Chromatography, High Pressure Liquid; D004798:Enzymes / Q000378:metabolism*; D005285:Fermentation; D006885:Hydroxybutyrates / Q000378:metabolism*; D007773:Lactates / Q000378:metabolism*; D009682:Magnetic Resonance Spectroscopy; D011108:Polymers / Q000378:metabolism*
chemical_list: D004798:Enzymes; D006885:Hydroxybutyrates; D007773:Lactates; D011108:Polymers; C031570:2-hydroxybutyric acid