Seven 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 was 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%dcw PHB with the addition of 1.2 g acetate L-1 and seven days under light:dark photoperiods. The highest EPS production was 59 mg L-1 with the addition of 1.2 g acetate L-1 and 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.

The aim of this study was to set the operating mode in regards to nutrients, temperature and light to use as a strategy to enrich a microbiome rich in cyanobacteria in polyhidroxybutyrate (PHB)-producers in order to enhance this biopolymer production. Alternate growth and accumulation phases were conducted for 179 days in a 3 L photobioreactor. Although, presence of green microalgae potentially reduced PHB production, the microbiome produced up to 22 % dry cell weight (dcw) PHB. Results suggested that this methodology could be applied to a robust microbiome rich in cyanobacteria to boost PHB production.

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Background Polyhydroxybutyrate (PHB) is a biopolymer synthetized by numerous bacterial species as intracellular carbon storage, which emerged as an alternative to fossil-based plastics. In this study, we elucidate the implications of harnessing photosynthetic microbiomes for the production of polyhidroxybutyrate (PHB). While previous studies have predominantly focused on photosynthetic cultures, such as cyanobacteria, maintained in axenic cultures, our work delves into uncharted territory by examining photosynthetic microbiomes. The distinctiveness of our approach lies in the utilization of complex microbial communities rather than single-strain systems under non-sterile conditions and maintained for a long-term period (197 days). The aim of this study was to set the operating mode in regards to nutrients, temperature and light to use as a strategy to enrich a microbiome rich in cyanobacteria in PHB-producers in order to enhance this biopolymer production. Alternate growth and accumulation phases were conducted for 197 days in a 3 L photobioreactor. Results The cyanobacteria rich microbiome achieved a PHB content of up to 22 % dry cell weight (dcw) PHB, indicating successful development of biopolymer-producing biomass. To optimize growth, N concentration was set at 25 mg·L-1 and darkness was ensured during PHB accumulation phase. Since we observed that presence of green microalgae potentially reduced PHB production, a low P concentration as well as high temperature were also implemented. Our findings underscore the significance of microbiome robustness in maintaining stable and efficient PHB production. Conclusions Results demonstrated the potential application of this methodology to enhance PHB production in a robust microbiome rich in cyanobacteria. This study breaks new ground by exploring the realm of photosynthetic microbiomes, shifting the focus from axenic cultures to more ecologically relevant systems.