Progress and challenges in producing polyhydroxyalkanoate biopolymers from cyanobacteria

Abstract

Growing concerns over conventional plastic materials and their detrimental effects on the environment have paved the way for exploring alternative sources for the production of bioplastics/biodegradable polymers. Polyhydroxyalkanoates (PHAs), being eco-friendly, biodegradable and renewable, with material properties comparable to conventional plastics, have gained significant attention for research and commercial ventures. Bacteria are reported to be the most efficient microbes in accumulating PHAs, where productivity up to 3.2 g L−1 h−1 can be attained. PHA production from a bacterial system, however, is found to be expensive. Cyanobacteria are now considered as prospective photoautotrophic systems with many advantages over higher plants for low-cost production of PHAs. Cyanobacteria have the potential to synthesize polyhydroxybutyrate (PHB) under photoautotrophic and chemoheterotrophic conditions using carbon substrates like glucose, acetate, and maltose, individually or in combination. Several studies have shown improvement in PHA yield in cyanobacteria by limiting nutrients and/or addition of various precursors. Under optimized conditions, PHB and P(3HB-co-3HV) co-polymer accumulation can reach up to 85 and 77% of dry cell weight (dcw) with a productivity of 13.3 and 1.6 mg L−1 h−1, respectively. Despite the strategic increase in the potential of PHA accumulation in cyanobacteria, the productivity does not suffice for economic production. Therefore, economically feasible production of PHA in cyanobacteria might be attained by technological improvements in various aspects like improvement in mass cultivation techniques, alternate low-cost organic substrates, use of various metabolic inhibitors to stimulate intracellular accumulation, and by suppression and overexpression of specific biosynthetic pathways by genetic engineering approaches.