Bacterial Production of Poly-b-hydroxybutyrate (PHB): Converting Starch into Bioplastics

Poly-β-hydroxybutyrate (PHB) is a thermoplastic polyester accumulated intracellularly by many microorganisms under unfavorable growth conditions. The features of PHB are biodegradable and biocompatible, and the physical properties are similar to polypropylene, which has attracted industrial attention as an environmentally degradable plastic for a wide range of agricultural, marine, and medical applications and appropriate substitutes for hydrocarbon-based plastics. Starch is a renewable carbon source from plant sources available abundantly in large quantities throughout the globe and has recently been used as a carbon source for PHB production. The utilization of starch in PHB production needs enzymatic hydrolysis for starch degradation since many microorganisms do not produce these enzymes natively. This suggests there is a need for exploitation of bacterial culture for the co-production of the starch-hydrolyzing enzyme (amylolytic bacteria) as well as PHB. Some bacteria have been reported capable to convert starch into PHB directly, which are from the genus Bacillus. The process of PHB production from starch by amylolytic bacteria is simultaneous saccharification and fermentation (SSF). The mechanism of bacteria synthesizing PHB from starch is divided into two groups, namely, the growth-associated PHB synthesis and the non-growth-associated PHB synthesis. The utilization of starch for PHB production is an economic strategy to reduce production costs of PHB as well as its applications in various fields. © The Editor(s) (if applicable) and The Author(s), under exclusive licence to Springer Nature Singapore Pte Ltd. 2021.