Bio-synthesis of poly(lactic acid) by wild type PHA-producing bacteria

聚乳酸（PLA）是由植物中的可再生资源合成的生物基聚合物之一。我们最近发现富养罗尔斯通氏菌（Ralstonia eutropica）的微生物培养系统中存在PLA低聚物，已知该系统在其体内形成其他脂肪族聚酯聚（3-羟基丁酸酯）。本研究旨在寻找最佳的细胞培养条件，以实现更好的大规模生产和更高分子量的PLA，建立聚酯在温和条件下的合适积累方式。研究发现，从富养罗伯茨菌培养系统中获得的PLA由D型乳酸重复单元组成，而从其他菌株细胞巨大芽孢杆菌中获得的PLA则含有D型和L型乳酸重复单元。 PLA 中乳酸单元的光学纯度取决于细胞株。还发现我们的细胞条件无法实现大批量生产或高分子量的 PLA。即使现在，我们仍在努力找出最佳的细胞培养条件。

Poly(lactic acid) (PLA) is one of bio-based polymers synthesized from renewable resources in plants. We have recently found that PLA oligomers existed in a microbial cultured system of Ralstonia eutropha (R. eutropha), which is known to form other aliphatic polyester, poly(3-hydroxybutyrate) within its body. This research aimed to find optimal cell-culture conditions for both better mass production and higher molecular weight of PLA, establishing the suitable accumulation manner of the polyester under mild conditions. PLA obtained from R. eutropha culture system was found to composed of D-formed lactic acid repeating units, while that from other strain cell, Bacillus megaterium, contained D- and L-formed ones. The optical purity of lactic acid units in PLA depended on the cell strains. It was also found that our cell conditions could not result in large mass production or high molecular weight of PLA. Even now, we are trying to find out the optimal cell-culture conditions.