Production of Polyhydroxyalkanoates, a bacterial biodegradable polymer

Abstract

There has been considerable interest in the development and production of biodegradable polymer to solve the current problem of pollution caused by the continuous use of synthetic polymer of petroleum origin. Polyhydroxyalkanoates (PHAs) are known to be accumulated as intracellular inclusion in some bacteria. The materials properties exhibited by PHAs, ranging from stiff, brittle to rubber-like makes it a close substitute for the synthetic plastic. The high cost of PHAs production has restricted its applications. The possibility of producing this polymer commercially and at comparable cost has been the main focus in this area.

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

“…For scl-PHAs, the monomer units are oxidized at positions other than the third carbons while for mcl-PHAs, all the monomers units are oxidized at the third position except in few cases (28). A lot of PHAs (mcl) containing various functional groups such as olefins, branched alkyls, halogens, aromatic and cyano have been reported (28,53,55). This flexibility of PHA biosynthesis makes it possible to design and produce related biopolymers having useful physical properties ranging from stiff and brittle plastic to rubbery polymers (26).…”

“…The PHA synthases of Alcaligenes eutrophus can only polymerize 3HAs (scl) while that of Pseudomonas oleovorans only polymerize 3HAs (mcl). For scl-PHAs, the monomer units are oxidized at positions other than the third carbons while for mcl-PHAs, all the monomers units are oxidized at the third position except in few cases (28). A lot of PHAs (mcl) containing various functional groups such as olefins, branched alkyls, halogens, aromatic and cyano have been reported (28,53,55).…”

“…A wide range of taxonomically and physiologically different natural bacteria and some archae accumulate PHAs as storage reserve materials and deposit them as insoluble granules in the cytoplasm (10,11,69,70,83,84). After the discovery of PHB from the bacterium B. megaterium (18), over 300 different bacteria, including Gram-negative and -positive species, have been reported to accumulate various PHAs (11,28,83,86,87). To date, most PHA-producing bacteria were found to be Gram-negative.…”

“…Once PHAs are extracted from bacterial cells, these polymers show crystalline, flexible, elastic and thermoplastic properties (22)(23)(24)(25). Further, they are synthesized from renewable carbon resources, based on agriculture or even on industrial wastes or fermentation feedstocks (25)(26)(27) so do not lead to the depletion of finite resources (28). Bacterial PHAs gained particular interest since they are completely biodegradable, non-toxic, biocompatible and also sources for commercially useful pool of chiral monomers (29)(30)(31)(32)(33).…”

“…Since their discovery, all these properties have made these microbial polyesters very attractive as a source of alternative biodegradable materials to conventional petrochemicalbased plastics (23,24,36). Therefore, they are considered for several applications in the packaging industry, biomedical, medicine, agriculture and food industry, or as raw materials for the synthesis of enantiomerically pure chemicals and the production of paints (28,(37)(38)(39). Due to wide industrial application, PHB are considered as green plastics.…”