Assessment of polyhydroxyalkanoates and polysaccharides production in native phototrophic consortia under nitrogen and phosphorous-starved conditions

Abstract

Growing demand for sustainable and eco-friendly alternatives to petroleum-based polymers has increased the interest in the microalgae-based production of polymers, specifically polyhydroxyalkanoates and polysaccharides. While most studies in microbial polymer production have primarily focused on axenic or genetically engineered cultures of cyanobacteria and eukaryotic algae, little is known about the potential of mixed phototrophic consortia. This study aimed to obtain and evaluate mixed photosynthetic consortia of different origins (natural and residual) as a novel approach for polyhydroxyalkanoates and polysaccharides accumulation. Activated sludge and freshwater samples were collected and inoculated in lab-scale photobioreactors to generate mixed photosynthetic consortia. After a preliminary screening for polymer-accumulating strains under nutrient-unbalanced conditions, the selected strains were subjected to a biphasic strategy (biomass accumulation and nutrient stress) to evaluate their polyhydroxyalkanoates and polysaccharide accumulation. First, cultures were subjected to a nutrient-rich phase to increase the biomass content and then deprived of nutrients (known as the polymer accumulation phase) to evaluate polyhydroxyalkanoates and polysaccharide yield. Findings in this study revealed that the highest polysaccharide yield for activated sludge biomass and freshwater consortia was 460 ± 16 and 320 ± 24 mg glucose g dried biomass−1, respectively. In contrast, the highest polyhydroxyalkanoates accumulation levels for both cultures were calculated at 5 mg polyhydroxyalkanoates g dried biomass−1. The efficacy of nutrient stress as a selective pressure strategy to develop mostly polysaccharides-accumulating consortia was demonstrated.