Strain-induced mesophase and hard-elastic behaviour of biodegradable polyhydroxyalkanoates fibers

Structure, phase transitions and mechanical properties of fibers of biodegradable bacterial polyester poly(β-hydroxybutyrate) and its random copolymers, prepared by gel-spinning and multistage melt-extrusion, were studied by X-ray diffraction, DSC and mechanical testing. It was found for the first time that as-spun fibers of the homopolymer display pronounced hard-elasticity. They exhibit reversible recovery of sample dimensions on loading and unloading, a behavior typical of hard-elastic fibers. It was also observed that elastic drawing leads to reversible formation of the strain-induced columnar mesophase with a 2D pseudohexagonal arrangement of conformationally disordered chains in addition to the orthorhombic crystalline and amorphous phases of the initial material. In contrast, binary and ternary random copolymers based on poly(β-hydroxybutyrate), being still crystallizable in spite of having relatively high comonomer content, behave like rubbers rather than true thermoplastics.     

Mutations to the active site of 3-ketoacyl-ACP synthase III (FabH) increase polyhydroxyalkanoate biosynthesis in transgenic Escherichia coli

Polyhydroxyalkanoate (PHA) production has been enhanced with engineered 3-ketoacyl-ACP synthase III (FabH) enzymes that accept diverse fatty acyl-ACP substrates and convert them to fatty acyl-CoA substrates for polymerization by PHA synthase enzymes resulting in the production of diverse polymers. Two mutations in the monomer supplying enzyme FabH, His244Ala and the Asn274Ala, were investigated to assess the impact of these mutations on PHA monomer production. PHA production increased more than six-fold with the mutation His244Ala in the FabH enzyme. Engineering of the FabH enzyme for improved PHA monomer supply led to a more productive system for PHA copolymer production.     

Creation of High-Yield Polyhydroxyalkanoates Engineered Strains by Low Energy Ion Implantation

Polyhydroxyalkanoates （PHAs）, as a candidate for biodegradable plastic materials, can be synthesized by numerous microorganisms. However, as its production cost is high in comparison with those of chemically synthesized plastics, a lot of research has been focused on the efficient production of PHAs using different methods. In the present study, the mutation effects of PHAs production in strain pCB4 were investigated with implantation of low energy ions. It was found that under the implantation conditions of 7.8×10^14 N^＋/cm^2 at 10 keV, a high-yield PHAs strain with high genetic stability was generated from many mutants. After optimizing its fermentation conditions, the biomass, PHAs concentration and PHAs content of pCBH4 reached 2.26 g/L, 1.81 g/L, and 80.08% respectively, whereas its wild type controls were about 1.24 g/L, 0.61 g/L, and 49.20%. Moreover, the main constituent of PHAs was identified as poly-3-hydroxybutyrates （PHB） in the mutant stain and the yield of this compound was increased up to 41.33% in contrast to that of 27.78% in the wild type strain.     

废水生物处理过程对微生物胞内PHA的影响

微生物合成的聚－β－羟基烷酸酯作为一种生物可降解高分子,不仅具有广阔的应用前景,而且在废水生物处理领域具有很高的研究价值。本文首先对微生物利用废水合成ＰＨＡ的代谢机理作了分析,然后分别介绍了与ＰＨＡ有关的两种不同的废水生物处理工艺及其关键影响因素,并对国内外在此领域的研究进展作了论述。     

基于嗜盐菌合成生物学的下一代工业生物技术

嗜盐微生物是在高盐、高pH环境中具备正常生长能力的极端微生物,是珍贵的科研素材和生产资源.相关研究通过对嗜盐菌合成生物学的改造和\"下一代工业生物技术\"的探索,实现了嗜盐工程菌在生物反应器中利用海水进行不灭菌连续发酵并产生类型多样、性能各异的聚羟基脂肪酸酯,且与其他高附加值化学品实现了联产.基于嗜盐菌的下一代工业生物技术...     

真氧产碱杆菌利用短链有机酸合成聚羟基烷酸酯

研究了真氧产碱杆菌利用单一以及混合短链有机酸作为碳源进行聚羟基烷酸酯(PHAs)的生物合成. 不同的碳氮浓度比对产物的形成有较大影响;在同样的碳源浓度下,较低氮源浓度更加有利于产物的合成;当短链有机酸浓度为8 g/L、硫酸铵浓度为0.3 g/L时对PHAs的合成最为有利.在4种短链有机酸分别单独用作碳源时,乳酸的消耗速度最快,其次为乙酸、丁酸以及丙酸;在单酸发酵条件下,丁酸的PHAs产量最高(2.72 g/L). 通过比较摇瓶以及5 L罐水平的混合酸发酵发现,发酵罐中的各项发酵指标均优于摇瓶. 研究还发现,真氧产碱杆菌在利用丙酸为碳源进行产物合成时,在发酵后期还伴随有乙酸产生.     

聚羟基烷酸酯的生物合成研究进展

聚羟基烷酸酯（PHA）是一类在众多微生物细胞内可合成的聚酯,由于其可完全生物降解,是一类可替代传统塑料的新型生物材料。该类聚酯在不同的微生物细胞内的生物合成途径已经被广泛和深入地研究。为降低其生产成本,实现工业化生产,筛选更高产的菌株和利用廉价碳源来合成PHA成为近年来的研究重点。本文介绍了PHA的在微生物细胞内的合成途径以及最近几年来生物合成PHA的研究进展。