Polyhydroxybutyrate (PHB): microbial synthesis and waste valorisation for sustainable bioplastics

Polyhydroxybutyrate (PHB), a biocompatible and biodegradable polymer, is an inevitable alternative source for the replacement of conventional plastics. PHB is an integral unit of various composite materials for its superior mechanical properties. The major source of PHB synthesis is through microbial metabolism under nutrient-limiting conditions. There are numerous applications of PHB in the fields of biomedical, food packaging, medicine, and agriculture. Recent research recognizes PHB as a useful biopolymer with modifiable characteristics for certain agronomic applications rather than just as a “green” substitute. In this review, the various microbial cell factories that produce PHB naturally along with the genetically modified organisms used so far have been discussed. In addition, the co-synthesis of other polymers with PHB and their microbial production strategies are elaborated. Central to this discussion is the application of PHB for three critical domains: biodegradable mulch films, precision seed coatings, and stimuli-responsive nutrient delivery systems. This review also deals with various substrates which include waste to low-economic value sources used for the production of PHB with economic and commercial importance. The roles of PHB in environmental sustainability along with its economic importance were also analyzed.