AbstractSeven photosynthethic microbiomes were collected from field environmental samples to test their potential in polyhydroxybutirate (PHB) and exopolysaccharides (EPS) production, two alternatives to chemical-based polymers. Microscope observations together with microbial sequence analysis revealed the microbiome enrichment in cyanobacteria after culture growth under phosphorus limitation. PHB and EPS production were studied under three culture factors (phototrophy, mixotrophy and heterotrophy) by evaluating and optimizing the effect of three parameters (organic and inorganic carbon and days under light:dark cycles) by Box-Behnken design. Results showed that optimal conditions for both biopolymers synthesis were microbiome-dependent; however, the addition of organic carbon boosted PHB production in all the tested microbiomes, producing up to 14%dcwPHB with the addition of 1.2 g acetate·L-1and seven days under light:dark photoperiods. The highest EPS production was 59 mg·L-1with the addition of 1.2 g acetate·L-1and four days under light:dark photoperiods. The methodology used in this article is suitable for enriching microbiomes in cyanobacteria, and for testing the best conditions for bioproducts synthesis for further scale up.