Microalgae and Cyanobacteria Species Valorization Towards Sustainable Bioplastics Production

The depletion of fossil resources and increasing plastic-derived pollution have become major environmental concerns. In this context, biodegradable biopolymers such as polyhydroxyalkanoates (PHA) have attracted considerable scientific interest. Microalgae and cyanobacteria represent promising photosynthetic microorganisms for sustainable bioplastic production. In this study, ten microalgal species (Parachlorella kessleri, Chlorella vulgaris, Chlorella minutissima, Tetraselmis tetrathele, Chromochloris zofigiensis, Acutodesmus obliquus, Euglena gracilis, Chlorococcum oleofaciens, Botryococcus braunii, and Coelastrella vacuolata) and four cyanobacterial species (Arthrospira platensis, Nostoc muscorum, Chlorogloeopsis fritschii, and Synechocystis sp.) were screened for growth and PHA accumulation. Cultivation was performed under autotrophic conditions, mixotrophic growth with acetate, mixotrophic growth in anaerobic digestion effluent, and nitrogen-depleted conditions. Arthrospira platensis showed the highest PHA content under autotrophic growth, reaching 4.3% w/w. Most species adapted successfully to anaerobic digestion effluent, achieving total nitrogen and phosphorus removal above 90% in most cases, although PHA accumulation remained low (0.6–1.3% w/w). Acetate supplementation and nitrogen limitation markedly enhanced PHA accumulation. Mixotrophic cultivation with acetate yielded up to 10.2% w/w in cyanobacteria, whereas nitrogen starvation increased accumulation further, with Synechocystis sp. reaching 14.4% w/w. Overall, cyanobacteria outperformed green microalgae, supporting their potential for sustainable bioplastic production. These findings provide a basis for species selection and future process optimization.