Microbiological and biotechnological aspects of biodegradable plastics: Poly(hydroxyalkanoates)

Abstract

Poly(3-hydroxyalkanoates) (PHAs) have been drawing much attention as biodegradable substitutes for conventional non-biodegradable plastics. Intensive research on the physiology, biochemistry and molecular genetics of the metabolism of PHAs during last two decades has increased our knowledge on the biosynthesis of these polyesters in bacteria and also showed various applications of these polymers. Prokaryotes synthesize a wide range of different PHAs and accumulate them as insoluble inclusions in the cytoplasm for storage of carbon and energy. Naturally, PHAs are synthesized from coenzyme A thioesters of the hydroxyalkanoic acids, which are synthesized during fatty acid metabolism. Due to similarities of physical and material properties with conventional plastics, PHAs can be recommended for application in various areas like industries, medicine, pharmacy and agriculture. They are thermoplastic and/or elastomeric, insoluble in water, enantiomerically pure, non toxic, biocompatible, piezoelectric and exhibit a high degree of polymerization. For economical production of PHAs, various bacterial strains have been exploited with new fermentation strategies and cheap renewable carbon sources. Transgenic plants have been studied for production of PHAs to compete with production cost of petroleum based bulk plastics. Metabolic engineering approaches have been used to expand the spectrum of utilizable substrate and also to improve PHAs production.