Polyhydroxyalkanoates: An Exotic Gleam in the Gloomy Tale of Plastics

Abstract

Polyhydroxyalkanoates (PHAs) are bio-polyesters of hydroxyalkanoates that accumulate intracellularly in case of prokaryotes, as cytoplasmic granules, under carbon rich and paucity of nitrogen, phosphorous, sulphur and oxygen where it can serve as carbon and energy source under nutrient limiting condition and/or environmental stress conditions. In adverse growth conditions, many bacteria have ability to store nutrients in form of PHA granules using their specific metabolic pathways during stationary growth phase, in the presence of high levels of carbon containing nutrient sources. Bacterial PHAs have generated attention as an alternative to petroleum derived synthetic plastics. It possesses the characteristic physico-chemical properties comparable to the synthetic plastics. These properties of PHAs can be improved by blending of PHAs with other natural polymer like starch, cellulose and semisynthetic polymers like poly lactic acids and polycaprolactones. Being eco-friendly, biodegradable and biocompatible; major PHAs such as, Polyhydroxybutyrate (PHB) and Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) have found numerous vital applications in pharmaceutical, biomedical, textile, cosmetic, agricultural, treatment of waste water and have been successfully employed for Food packaging industries. This review provides a comprehensive knowledge about the world of PHAs covering its major aspects, namely its chemical nature and structure, biosynthesis, various methods of screening of potential PHA producing bacteria along with properties, several techniques used for its recovery and further characterization.