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

聚乳酸是利用植物中的可再生资源合成的一种生物基聚合物。我们最近发现，在一种微生物培养系统中存在着聚乳酸低聚体，这种细菌在体内还能形成其他脂肪族聚酯--聚(3-羟基丁酸酯)。本研究旨在为聚乳酸的大批量生产和较高的相对分子质量寻找最佳的细胞培养条件，建立在温和条件下聚脂的适宜积累方式。富营养化芽孢杆菌培养体系中的聚乳酸由D-型乳酸重复单元组成，而其他菌株巨大芽孢杆菌的聚乳酸由D-型和L-型乳酸重复单元组成。聚乳酸中乳酸单元的光学纯度取决于细胞株。实验还发现，在我们的细胞条件下，不能实现大批量生产或高分子量的聚乳酸。即使是现在，我们也在努力寻找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.