Perspectives for Biotechnological Production and Utilization of Biopolymers: Metabolic Engineering of Polyhydroxyalkanoate Biosynthesis Pathways as a Successful Example

Abstract

This article provides an overview of biopolymers, classed according to their chemical structures, function and occurrence, the principles of biosynthesis and metabolism in organisms. It will then focus on polyhydroxyalkanoates (PHA) for which technical applications in several areas are currently considered. PHAs represent a complex class of bacterial polyesters consisting of various hydroxyalkanoic acids that are synthesized by bacteria as storage compounds for energy and carbon if a carbon source is present in excess. Poly(3‐hydroxybutyrate), poly(3HB), is just one example. Most other PHAs are only synthesized if pathways exist which mediate between central intermediates of the metabolism or special precursor substrates on one side and coenzyme A thioesters of hydroxyalkanoic acids, which are the substrates of the PHA synthase catalyzing the polymerization, on the other side. During the last decade, basic and applied research have revealed much knowledge about the biochemical and molecular basis of the enzymatic processes for the synthesis of PHAs in microorganisms. The combination of detailed physiological studies, utilization of the overwhelming information provided by the numerous genome sequencing projects, application of recombinant DNA technology, engineering of metabolic pathways or enzymes and molecular breeding techniques applied to plants have provided new perspectives to produce these technically interesting biopolymers by novel or significantly improved biotechnological processes or by agriculture. Some examples for successful in vivo and in vitro engineering of pathways suitable for the synthesis and biotechnological production of PHAs consisting of medium‐chain‐length 3‐hydroxyalkanoic acids and short‐chain‐length hydroxyalkanoic acids will be provided.

Structure of the Catalytic Domain of the Class I Polyhydroxybutyrate Synthase from Cupriavidus necator

“…These polymers have garnered considerable biotechnological interest, because they have properties ranging from thermoplastics to elastomers, depending on how the monomer units are substituted, with alkyl substituents ranging from CH 3 to C 9 H 19 (3,4). Additionally, PHAs are biodegradable, making them an environmentally friendly and sustainable alternative to petroleum-based plastics (5,6). Such biologically derived materials are used in specialty markets, such as medical devices; however, they are currently not economically competitive in largescale production with traditional petroleum-based plastics.…”

“…Polyhydroxyalkanoic acids (PHAs) 5 are polyoxoesters synthesized by many bacterial species as a means of carbon storage under nutrient-limited conditions in which carbon is abundant (1)(2)(3). These polymers have garnered considerable biotechnological interest, because they have properties ranging from thermoplastics to elastomers, depending on how the monomer units are substituted, with alkyl substituents ranging from CH 3 to C 9 H 19 (3,4).…”

Bacterial polyhydroxyalkanoates-eco-friendly next generation plastic: Production, biocompatibility, biodegradation, physical properties and applications

“…(1) Packaging, molding and coating PHAs are natural and biodegradable thermoplastic polyesters, and hence the majority of their applications are as replacements for petrochemical polymers currently in use for packaging and coating applications (26,31,230,244). They can be used in a wide variety of products including bags, containers, paper coatings, pens, golf tees, razors, feminine hygiene products, diaper backsheets, utensils, cosmetic containers, bottles, cups and materials for food packaging (26,28,31,38,190).…”

Exploring biodegradable polymer production from marine microbes

“…At the same time, storage polymer production was not only seen in Gram-negative but also in Grampositive bacteria, anaerobic (non-sulfur and sulfur purple bacteria) and aerobic (cyanobacteria), and also in some archaebacteria [47,48]. So far approximately 150 different monomers of various structures (saturated, unsaturated, branched, straight, and aromatic) of over 90 genera have been reported [49,50].…”