Downstream processing of Scenedesmus sp. to obtain biostimulants.

There is a growing interest in applying natural products in agriculture to stimulate growth and/or resistance of plants, and ultimately to increase productivity without causing further environmental degradation. Microalgae synthesize a wide variety of high-value products, including phytostimulants. Even if applied to plants in small proportions, these substances can increase crop yield and protect the plants from biotic and abiotic stress. The microalga Scenedesmus sp. was grown in simulated treated wastewater to demonstrate its ability to bioremediate and to be a source of phytostimulants. Optimization of the cell disruption method is required to improve the extraction of biomolecules. Therefore, in this work, cell disruption methods, namely high-pressure homogenization (HPH), ultrasonication (US), and hydrolysis, were compared. To evaluate the biostimulant potential, extracts were evaluated using the germination index of watercress seeds, rooting bioassay in mung bean and cucumber, and cotyledon expansion in cucumber. There was a 44% increase in the germination index when watercress were treated with a combination of HPH and enzymatic hydrolysis disrupted extracts. In the mung bean bioassay, the best results were obtained with extracts prepared by HPH and enzymatic hydrolysis, achieving 160% rooting compared to 100% rooting in the control treated with distilled water. For rooting activity in cucumber, the best results were obtained after biomass pre-treatment by HPH, both with or without the enzymatic hydrolysis treatment, achieving maximum root development values of 275%. Differences in cotyledon expansion were not significant. This work demonstrated the biostimulant effect of Scenedesmus sp. biomass on three plant species. HPH and enzymatic hydrolysis increased the overall effect although their inclusion might not be economical. [ABSTRACT FROM AUTHOR]