Designing Microorganisms for Production of Diverse Biopolymers

Microbial polyhydroxyalkanoates (PHA) have been developed as bioplastics for the past many years. PHA have diverse structures, at least 150 monomers have been found in the PHA polymer chains. However, it has been very difficult to precisely control the PHA polymer structures. In this presentation, all the PHA synthesis pathways have been studied, microorganisms have been designed with synthetic pathways allowing precise control of the PHA structures. The synthetic organisms can now make various PHA homopolymers, random copolymers, block copolymers, even graft polymers can be produced combined microbial and chemical synthese. For example, commercial PHA are normally poly-3-hydroxybutyrate (PHB), copolyesters of 3-hydroxybutyrate and 3-hydroxyhexanoate (PHBHHx), copolyesters of 3-hydroxybutyrate and 4-hydroxybutyrate (P3HB4HB), as well as copolyesters of 3-hydroxybutyrate and 3-hydroxyvalerate (PHBV). The designed organisms produced a series of novel PHA including homopolymers, random copolymers and block copolymers. For example, poly-3-hydroxypropionate (P3HP), poly-4-hydroxybutyrate (P4HB), poly-3-hydroxydecanoate (P3HD) and poly-3-hydroxydodecanoate (P3HDD) et al. Random copolymers containing defined monomer compositions can also be microbially produced. More importantly, block copolymerization containing various block such as diblock copolymers of PHB-b-P4HB, PHB-b-PHHHx, P3HP-b-P4HB, PHBHHx-b-PHDD et al  have been produced. They remarkably increased the diversity of PHA structures and properties. By manipulating the block compositions, the polymer properties can be easily controlled. Now, PHA industry will be entering a functional polymer era, which allows PHA competitiveness not by the low cost but by its functionality. We will soon experience ultra-strong, shape memory, gas selective permeability and other environmentally responsive PHA.