Biopolyester synthesis

Fig. 3 Metabolic routes towards biopolyester synthesis. Dashed lines represent engineered biosynthesis routes. Triangles depict targets for inhibitors enabling biopolyester synthesis. Enzymes indicated on shaded boxes on solid lines are biopolyester biosynthesis enzymes. With kind permission from Springer Science+Business Media [7]...

Extensive studies in the molecular biology and physiology of the bacterial biopolyester synthesis has been made in the last decade. Previous research activities were mainly aimed at the biotechnological production of the extracted and semicrystalline thermoplastic polyester materials. Recently, however, it has been recognized that the intracellular polyester inclusions or those derived from in vitro synthesis can be considered as natural bionanoparticles. 

Yu, J and Stahl, H. (2008) Microbial utilization and biopolyester synthesis of bagasse hydrolysates. Bioresource Technology, 99 8042-8048. 

PHAs can consist of a diverse set of repeating unit structures and have been studied intensely because the physical properties of these biopolyesters can be similar to petrochemical-derived plastics such as polypropylene (see Table 1). These biologically produced polyesters have already found application as bulk commodity plastics, fishing lines, and for medical use. PHAs have also attracted much attention as biodegradable polymers that can be produced from biorenewable resources. Many excellent reviews on the in vivo or in vitro synthesis of PHAs and their properties and applications exist, underlining the importance of this class of polymers [2, 6, 7, 12, 26-32]. 

Polymers derived from renewable resources (biopolymers) are broadly classified according to the method of production (1) Polymers directly extracted/ removed from natural materials (mainly plants) (e.g. polysaccharides such as starch and cellulose and proteins such as casein and wheat gluten), (2) polymers produced by "classical" chemical synthesis from renewable bio-derived monomers [e.g. poly(lactic acid), poly(glycolic acid) and their biopolyesters polymerized from lactic/glycolic acid monomers, which are produced by fermentation of carbohydrate feedstock] and (3) polymers produced by microorganisms or genetically transformed bacteria [e.g. the polyhydroxyalkanoates, mainly poly(hydroxybutyrates) and copolymers of hydroxybutyrate (HB) and hydroxyvalerate (HV)] [4]. 

As it was previously said, biodegradable polymers tend to consist of ester, amide, or ether bonds. In general, biodegradable polymers can be separated into two main groups based on their structure and synthesis Agro-polymers, or those derived from biomass [7] and biopolyesters, which are those derived from microorganisms or synthetically made from either naturally or synthetic monomers (Fig 24.1). 

Poirier Y (2002) Polyhydroxyalkanoate synthesis in plants as a tool for biotechnology and basic studies of Upid metabolism. Prog Lipid Res 41 131-155 Poirier Y, Gruys KJ (2001) Production of PHAs in transgenic plants. In Doi Y, Steinbiichel A (eds) Biopolyesters. Wiley-VCH, Weinheim, pp 401 35 Poirier Y, van BeUen JB (2008) Production of renewable polymers from crop plants. Plant J 54 684-701... 

Beniitez J.J., Garcia-Segura R., Heredia A., Plant biopolyester cutin A tough way to its chemical synthesis, Biochim. 

Like polymers, biodegradable polymers have been classified using distinct methods, including methods based on polymer origin (synthesis), renewability content, and biodegradability level. The most prominent and well-established method is the classification based on synthetic procedmes. In broad terms, these polymers are classified into two main categories (i) agropolymers (obtained from biomass) and (ii) biopolyesters (natural or synthetic biopolymers). Biopolyesters is itself a broad term that includes three subclasses (a) microbially produced polymers (b) polymers synthesized... 

Attempts to demonstrate the feasibility of profitable production on an agricultural scale are the next steps [282]. Poirier s group has proposed a number of oilseed crops that could be targeted for seed-specific PHA production, like rapeseed (closely related to A. thaliana), sunflower and soybean. Some of these are already under investigation by major companies. Depending on whether accumulation levels can be further increased PHAs stored in plants have any deleterious effects on crop value in other respects synthesis of PHAs other than PHB can be induced and extraction of the biopolyesters is feasible at reasonable costs, the cost of PHAs produced in plants might be lowered enough to make them competitive with conventional plastics. But the tendency of arable land to become one of the most precious commodities on Earth [286] will present a formidable obstacle to applications in this field. 

Polymers produced by classical chemical synthesis from renewable bio-derived monomers A good example is polylactate, a biopolyester polymerized from lactic acid monomers. The monomer itself is produced by fermentation of carbohydrate feedstock. 

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