Chemical and Physical Affinity of Microalga-Azospirillum Consortium Co-cultured in Suspension During CO2 Fixation from Biogas

This study evaluated the ability of the bacterium Azospirillum brasilense to establish a synergic association with the microalgae Chlorella sp. and Scenedesmus sp. co-cultured in suspension and supplied with biogas (75% CH4-25% CO2). The results demonstrated that under the stressful composition of biogas, signal molecule production, such as indole-3-acetic acid (IAA) and tryptophan (Trp) production by the bacterium and microalgae, respectively, allowed the maintenance of their affinity and mutualistic association. Chlorella sp. and Scenedesmus sp. co-cultured in suspension with the bacterium showed higher CO2 fixation rates, 0.29 +/- 0.05 and 0.31 +/- 0.06 g.L-1.day(-1), respectively, than cultured alone, 0.17 +/- 0.04 and 0.22 +/- 0.03 g.L-1.day(-1). Similarly, biomass production of Chlorella sp. (1.4 +/- 0.4 g.L-1) and Scenedesmus sp. (1.6 +/- 0.5 g.L-1) and their cell composition-mainly carbohydrates and proteins-also enhanced in both microalgae interacting with the bacterium. Overall, these results indicate that, co-cultured in suspension, this consortium microalga-A. brasilense did not change its mutualistic interaction during the specific conditions of CO2 capture from biogas.