Polyhydroxybutyrate (PHB) accumulation by a mangrove isolated cyanobacteria Limnothrix planktonica using fruit waste

Cyanobacterial polyhydroxybutyrate (PHB) is preferred over bacteria for low-cost production due to its photoautotrophic nature and lower carbon requirement. Considering its impact on the environment and circular economy, the valorization of fruit waste is the need of the hour. In the present study, fruit peels of banana, orange, pea, jackfruit, watermelon and waste flowers were tried as carbon sources for mangrove-isolated cyanobacteria Limnothrix planktonica to accumulate PHB. Alterations in the ASN-III culture medium and the introduction of untreated and pre-treated (acid/alkali-treated) peels as carbon sources are tried to enhance PHB. Banana peel showed the maximum PHB accumulation potential of 25.73 mg/L on the 12th day of incubation, followed by jackfruit (22.46 mg/L) and watermelon peels (20.72 mg/L); whereas, commercial carbon sources showed lower PHB accumulation up to 19.26 mg/L and 18.21 mg/L with fructose and glucose respectively. PHB accumulation was boosted to 5-fold higher (39.39 mg/L) in NP deficiency medium along with banana peel supplement, as compared to photoautotrophic conditions (8.49 mg/L) after the 9th day of incubation. Additionally, the PHB obtained by using the fruit wastes has a higher molecular weight than the PHB accumulated during photoautotrophic conditions. Optimization of parameters using fruit wastes and characterization of PHB would lead to its potential use.