Abstract
Polyhydroxyalkanoates (PHAs) are a group of biopolymers produced in various microorganisms as carbon and energy reserve when the main nutrient, necessary for growth, is limited. PHAs are attractive substitutes for conventional petrochemical plastics, as they possess similar material properties, along with biocompatibility and complete biodegradability. The use of PHAs is restricted, mainly due to the high production costs associated with the carbon source used for bacterial fermentation. Cyanobacteria can accumulate PHAs under photoautotrophic growth conditions using CO2 and sunlight. However, the productivity of photoautotrophic PHA production from cyanobacteria is much lower than in the case of heterotrophic bacteria. Great effort has been focused to reduce the cost of PHA production, mainly by the development of optimized strains and more efficient cultivation and recovery processes. Minimization of the PHA production cost can only be achieved by considering the design and a complete analysis of the whole process. With the aim on commercializing PHA, this review will discuss the advances and the challenges associated with the upstream processing of cyanobacterial PHA production, in order to help the design of the most efficient method on the industrial scale.
Highlights
Petroleum-based polymers are relatively inert, versatile, and durable; they have been used in industry for more than 70 years [1]
Polyhydroxyalkanoates (PHAs) are a class of naturally occurring polymers produced by microorganisms [1,6,7], among which poly (3-hydroxybutyrate) (PHB) is the most studied biodegradable polymer that accumulates in bacteria in the form of inclusion bodies as carbon reserve material when cells grow under stress conditions [5,8]
Cyanobacteria are equipped with superior photosynthetic machinery, showing higher biomass production rates compared to plants and can convert up to 3–9% of the solar energy into biomass [28,29]
Summary
Petroleum-based polymers are relatively inert, versatile, and durable; they have been used in industry for more than 70 years [1]. Attention has been focused to reduce the production cost, mostly by selecting more economically feasible and efficient carbon substrates for PHB production such as whey, hemicellulose, sugar cane, agricultural wastes, and molasses [5,18,19,20]. In this context, PHB production using cyanobacteria from more sustainable resources, such as CO2, has gained importance. The authors believe that a proper-time resolved quantification of the process will aid in a better understanding for process manipulation and optimization of industrial production
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