Synergic association of the consortium Arthrospira maxima with the microalga growth-promoting bacterium Azospirillum cultured under the stressful biogas composition

The present study evaluates the association of the blue–green microalga Arthrospira maxima (Spirulina), which is known for its CO₂ fixation, biomass, and high-value metabolite production, with the microalga growth-promoting bacterium Azospirillum brasilense under the stressful composition of biogas. The results demonstrated that A. maxima co-cultured with A. brasilense under the high CO₂ (25%) and methane (CH₄; 75%) concentrations of biogas recorded a CO₂ fixation rate of 0.24 ± 0.03 g L^–1 days^–1, thereby attaining a biomass production of 1.8 ± 0.03 g L^–1. Similarly, the biochemical composition quality of this microalga enhanced the attainment of higher contents of carbohydrates, proteins, and phycocyanin than cultured alone. However, metabolites other than tryptophan (Trp) and indole-3-acetic acid could have supported this beneficial interaction. Overall, the results demonstrate that this prokaryotic consortium of A. maxima–A. brasilense established a synergic association under biogas, which represents a sustainable strategy to improve the bio-refinery capacity of this microalga and increase the usefulness of A. brasilense in multiple economic sectors.