Plastic is one of the most versatile and widely used materials in the world. However, the traditional petroleum-based plastic has brought severe ‘white pollution’ due to its nondegradability. Approximately 40 million tons of plastic waste is generated in the whole world each year.

Bio-plastic can replace most of the petroleum-based plastic, and it is the most promising alternative material to solve the present problem. Poly lactate (PLA) is the major type consumed bio-plastic, and the market continues to grow rapidly. There are also some drawbacks restrict its potential applications. The incorporation of poly D-lactate into PLA is able to improve the mechanical performance, thermal resistance, and hydrolysis resistance of PLA-based materials.

The optical purity of polymerization grade D-lactate is as high as 98%, it is hard to meet the requirement by chemical synthesis or biosynthesis in previous studies. Recently, a research team led by Prof. ZHAO Guang from Qingdao Institute of Bioenergy and Bioprocess Technology (QIBEBT), Chinese Academy of Sciences (CAS), developed a high efficiency cell factory to successfully obtain 100% optical purity D-lactate.

The researchers from ZHAO’s team found that Klebsiella pneumoniae produce D-lactate effectively. Then metabolic analysis and restruction was systematically carried out, the optical purity of D-lactate achieved 100% for the first time. The engineered strains obtained a wide carbon sources spectrum, not only common carbon sources such as glucose and glycerol, but also pentose such as xylose and arabinose from lignocellulose hydrolysate. Moreover, anaerobic condition was not necessary for fermentation, which can simplify the experimental instrument requirements and reduce the production cost.

This study provides new insights into potential of optically pure D-lactate by K. pneumoniae from cheap carbon sources. The related progresses were published in Microbial Cell Factories and Polymers. The research was supported by the Shandong Province Natural Science Funds and Shandong Province Postdoctoral Innovation Funds.

Figure: Optically pure D-lactate fermentation: From cheap carbon sources to value-added products (Image by FENG Xinjun)