Species composition determines bioplastics production in photosynthetic microbiomes: strategy to enrich cyanobacteria PHB-producers

Abstract

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.