Growth and metabolism enhancement in microalgae co-cultured in suspension with the bacterium Azospirillum brasilense under heterotrophic conditions

The mutualistic interactions of microalgae with other microorganisms can be altered by different culture conditions or environment factors. The mutualistic interaction of the bacterium Azospirillum brasilense co-cultured in suspension with the microalgae Chlorella sp. and Scenedesmus sp. under heterotrophy was evaluated in this study. The results demonstrated that the production of indole-3-acetic acid (IAA) and tryptophan (Trp) by the bacterium and microalgae, respectively, allowed maintain their affinity and mutualistic association under a heterotrophic regime. However, the glucose uptake of the consortium depends on the culture system, immobilized, or in suspension. Co-cultured in suspension with the bacterium, the biomass production of Chlorella sp. (0.8 ± 0.1 g L−1) and Scenedesmus sp. (0.9 ± 0.1 g L−1) and cell compound accumulation—mostly carbohydrates and proteins—were higher than when each microalga was cultured alone. Overall, these results demonstrated that, co-cultured in suspension, A. brasilense can be a suitable partner to Chlorella sp. and Scenedesmus sp., highlighting that the compatibility and mutualistic interaction of this consortium does not change under different culture systems and growth conditions. Also, this study expands the biotechnological potential of this consortium microalgal-Azospirillum as well as its incidence in different bioprocesses supported by microalgae.