Microalgae-bacteria interaction in alginate beads prevents the negative effect of copper oxide nanoparticles on the growth and metabolism of Scenedesmus sp

Owing to their extensive application, copper oxide nanoparticles (CuO NPs) has become common components in wastewater that arrives at wastewater treatment plants. Immobilization of microalgae and bacteria cells in alginate beads has been proposed as a potential tool for tertiary wastewater treatment processes to prevent the negative effect of biotic stress on immobilized microorganisms. Nonetheless, the effect of the emerging CuO NP contaminants on microalgae-bacteria interaction has not been evaluated. Thus, the aim of this study was to assess the effect of CuO NPs (1, 10, and 100 ppm) on the growth and metabolism of the microalga Scenedesmus sp. immobilized alone and concomitantly with the bacterium Azospirillum brasilense . Low CuO NP concentrations (1 ppm) induced higher growth rates for both microorganisms, regardless of their immobilization status (an average increase of 117.9% for Scenedesmus sp. and 73% for A. brasilense ). In addition, microalga-bacterium co-immobilization enhanced the growth of Scenedesmus sp. in the control group (without NPs: 2.95 ± 0.32 cells × 10 4 bead −1 ) and in the presence of low (1 ppm: 8.69 ± 3.19 cells × 10 4 bead −1 ) and high NP concentrations (100 ppm: 2.39 ± 1.03 cells × 10 4 bead −1 ) compared with microalgae immobilized alone (without NPs: 1.79 ± 0.48 cells × 10 4 bead −1 ; 1 ppm: 6.82 ± 1.54 cells × 10 4 bead −1 ; 100 ppm: 1.32 ± 0.27 cells × 10 4 bead −1 ). Moreover, the interaction between Scenedesmus sp. and A. brasilense in the presence of 1 ppm CuO allowed for higher protein and carbohydrate contents than did the other treatments. The negative effect of the CuO NPs on the growth of the microorganisms was only observed at the higher concentration (100 ppm) when the microorganisms were immobilized alone. These results demonstrate that the use of immobilized cells can prevent the negative effects of emerging contaminants such as CuO NPs on microalgal growth. Moreover, the microalgae-bacteria interaction in the presence of CuO NPs allowed for identifying microalgae biomasses with high contents of the metabolites of interest.