Biosynthesis of polyesters and polyamide building blocks using microbial fermentation and biotransformation

Biopolymers can be a green alternative to fossil-based polymers and can contribute to environmental protection because they are produced using renewable raw materials. Biopolymers are composed of various small subunits (building blocks) that are the intermediates or end products of major metabolic pathways. Most building blocks are secreted directly outside of cells, making downstream processes easier and more economic. These molecules can be extracted from fermentation broth and polymerized to produce a variety of biopolymers, e.g., polybutylene terephthalate, polyethylene terephthalate, polytrimethylene terephthalate, nylon-5,4 and nylon-4,6, with applications in medicine, pharmaceuticals, and textiles. Microbes are unable to naturally produce these types of polymers; thus, the production of building blocks and their polymerization is a fascinating approach for the production of these polymers. In comparison to naturally occurring biopolymers, synthesized polymers have improved and controlled structures and higher purity. The production of monomer units provides a new direction for polymer science because new classes of polymers with unique properties that were not previously possible can be prepared. Furthermore, the engineering of microbes for building-block production is an easy process compared to engineering an entire biopolymer synthesis pathway in a single microbe. Polyesters and polyamide polymers have become an important part of human life, and their demand is increasing daily. In this review, recent approaches and technology are discussed for the production of polyester/polyamide building blocks, i.e., 2-hydroxyisobutyric acid, 3-hydroxypropionic acid, mandelic acid, itaconic acid, adipic acid, terephthalic acid, succinic acid, 1,3-propanediol, 2,3-butanediol, 1,4-butanediol, 1,3-butanediol, cadaverine, and putrescine.