Sustainable production of polyhydroxybutyrate from autotrophs using CO2 as feedstock: Challenges and opportunities

[Display omitted] •Advances on cultivation of autotrophs on CO2 are discussed.•Production of polyhydroxybutyrate by autotrophs/other microalgae reviewed.•Circular biorefinery approach needed for higher microalgae production and CO2 capture.•Optimizing mass transfer parameters can enable better CO2 utilization from flue gas.•New/hybrid approaches needed for in strains improvement through molecular tools. Due to industrialization and rapid increase in world population, the global energy consumption has increased dramatically. As a consequence, there is increased consumption of fossil fuels, leading to a rapid increase in CO2 concentration in the atmosphere. This accumulated CO2 can be efficiently used by autotrophs as a carbon source to produce chemicals and biopolymers. There has been increasing attention on the production of polyhydroxybutyrate (PHB), a biopolymer, with focus on reducing the production cost. For this, cheaper renewable feedstocks, molecular tools, including metabolic and genetic engineering have been explored to improve microbial strains along with process engineering aspects for scale-up of PHB production. This review discusses the recent advents on the utilization of CO2 as feedstock especially by engineered autotrophs, for sustainable production of PHB. The review also discusses the innovations in cultivation technology and process monitoring while understanding the underlying mechanisms for CO2 to biopolymer conversion.