Bacterial Polyhydroxyalkanoates: Recent Trends in Production and Applications
Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polymers accumulated in microorganisms as intracellular carbon and energy reserve, which are utilized when the external carbon supply is limited. PHAs have gained popularity as ‘green polyme
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Bacterial Polyhydroxyalkanoates: Recent Trends in Production and Applications Aneesh Balakrishna Pillai and Hari Krishnan Kumarapillai
Abstract
Polyhydroxyalkanoates (PHAs) are biodegradable and biocompatible polymers accumulated in microorganisms as intracellular carbon and energy reserve, which are utilized when the external carbon supply is limited. PHAs have gained popularity as ‘green polymers’ which can be a substitute for petroleum-derived plastics due to their plastic-like properties, possibility to produce from renewable resources, and complete biodegradability in environment. The high production cost is the main hindrance to the wide spread use of these materials. Research is progressing with an aim to produce PHAs from cheap and easily available carbon sources and from waste materials and thereby make them economically competitive with conventional plastics. This review is focused on recent advances in the field of bacterial production of polyhydroxyalkanoates and their applications. Keywords
Biopolymers • Polyhydroxyalkanoates • Poly-3-hydroxybutyrate • PHA biosynthesis • PHA copolymers • Bacterial fermentation
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Introduction
Polyhydroxyalkanoates (PHAs) are polyoxoesters accumulated in eubacteria and Archaea as carbon and energy storage components in response to nutrient stress conditions (Rehm 2003). They are synthesized when a carbon source is available in A. Balakrishna Pillai • H.K. Kumarapillai (*) Environmental Biology Laboratory, Rajiv Gandhi Centre for Biotechnology, Poojappura, Thiruvananthapuram 695014, Kerala, India e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2017 P. Shukla (ed.), Recent Advances in Applied Microbiology, DOI 10.1007/978-981-10-5275-0_2
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excess, and other essential nutrients such as nitrogen and phosphorus are growth limiting (Anderson and Dawes 1990). They are stored in their cytoplasm as water insoluble PHA granules (0.2–0.5 μm diameter) with a phospholipid monolayer (Rehm 2003; Urtuvia et al. 2014), and this carbon sink is mobilized by intracellular PHA depolymerases when carbon starvation occurs (Gao et al. 2001). They have unique combination of biodegradability, biocompatibility and controllable thermal- mechanical properties (Chen and Wu 2005). PHAs can be synthesized from renewable resources and are entirely degraded to CO2 and H2O under environmental conditions (Jendrossek and Handrick 2002). Hence they have attracted extensive interest as recyclable, eco-friendly, biodegradable alternatives to petroleum-based plastics (Wang et al. 2012b). In spite of the intensive research carried out on bacterial PHAs world over, their production cost is still far higher than the price of petroleum-derived plastics (Castilho et al. 2009). PHAs are thermoplastic or elastomeric polyesters having molecular weights on the order of 2 × 105 to 3 × 106 and are made up of enantiomerically pure R-hydroxyalkanoic acid monomers (Philip et al. 2007). Generally, a PHA molecule consists of 600–35,000
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