Growth, biostimulant and biopesticide activity of the MACC-1 Chlorella strain cultivated outdoors in inorganic medium and wastewater

The use of wastewater (WW) for cultivation contributes to the sustainability of microalgae production due to the reduced costs of cultivation. The main objective of this work was to study growth, physiological performance and bioactivity of the microalgae strain Chlorella vulgaris MACC-1 grown in two nutrient sources – inorganic BG-11 medium and centrate from municipal WW. For the comparison, two thin-layer cultivation units – thin-layer cascade and a novel, thin-layer raceway pond – were used. The cultures grew well in both units showing good photosynthetic activity. The germination index of watercress seeds, as well as the auxin-like activity in mung bean and cytokinin-like activity in wheat growth tests were used to evaluate the biostimulant potential. The slight increase on the germination index was determined in C. vulgaris cultures grown in BG-11, but the biomass revealed no biostimulant activity when cultivated in WW. On the other hand, the antibacterial and antifungal activities determined by antagonism bioassay using dual cultures were significantly higher when grown in WW. We expect that the antimicrobial activities may be induced by WW-microbes and the biostimulating effect could probably be suppressed by the presence of some inhibiting substances. The results revealed a clear interplay among ambient irradiance intensity, growth rate, maximum quantum yield of PSII, Fv/Fm and oxygen production/respiration.