Perpetual bioplastic production by a cyanobacteria-dominated microbiome

Departing from the conventional axenic and heterotrophic cultures, our research ventures into unexplored territory by investigating the potential of photosynthetic microbiomes for polyhydroxybutyrate (PHB) production. A cyanobacteria-rich microbiome was harnessed for PHB production in a 3 L photobioreactor under non-sterile conditions. The robust culture achieved up to 28 %dcw PHB over 108 days of alternating growth and accumulation phases. Nile Blue staining and Transmission Electron Microscope visualization successfully confirmed the presence of PHB granules within cyanobacteria cells. Analysis through proton Nuclear Magnetic Resonance further validated the extracted polymer as PHB. In addition, the overexpression of the enzyme PHA synthase throughout the accumulation phase correlated directly with the increased PHB production. Also, gene expression changes suggested that initially, glycogen served as the primary storage compound. However, with prolonged macronutrient stress, there was a shift of the carbon flux towards favoring PHB synthesis. Overall, it was demonstrated for the first time the feasibility of using a phototrophic microbiome to continuous production of PHB in a non-sterile system, contributing to advancing in the field of biopolymer production and offering valuable insights into the metabolic pathways involved. ### Competing Interest Statement The authors have declared no competing interest.