Taizo Kabe

One-Pot Microbial Production, Mechanical Properties, and Enzymatic Degradation of Isotactic P[(R)-2-hydroxybutyrate] and Its Copolymer with (R)-Lactate

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].

In vitro synthesis of linear α-1,3-glucan and chemical modification to ester derivatives exhibiting outstanding thermal properties

Bio-based polymer is considered as one of potentially renewable materials to reduce the consumption of petroleum resources. We report herein on the one-pot synthesis and development of unnatural-type bio-based polysaccharide, α-1,3-glucan. The synthesis can be achieved by in vitro enzymatic polymerization with GtfJ enzyme, one type of glucosyltransferase, cloned from Streptococcus salivarius ATCC 25975 utilizing sucrose, a renewable feedstock, as a glucose monomer source, via environmentally friendly one-pot water-based reaction. The structure of α-1,3-glucan is completely linear without branches with weight-average molecular weight (Mw) of 700 kDa. Furthermore, acetate and propionate esters of α-1,3-glucan were synthesized and characterized. Interestingly, α-1,3-glucan acetate showed a comparatively high melting temperature at 339 °C, higher than that of commercially available thermoplastics such as PET (265 °C) and Nylon 6 (220 °C). Thus, the discovery of crystalline α-1,3-glucan esters without branches with high thermal stability and melting temperature opens the gate for further researches in the application of thermoplastic materials.