Haematococcus pluvialis culture contaminated with chytrids: growth management and astaxanthin production

Haematococcus pluvialis Flotow has gained growing interest last years due to its high content of astaxanthin. The quick expansion of its culture worldwide has been accompanied with report of several cases of fungal contamination, mainly with chytrids, causing serious losses in astaxanthin production. Although chemical fungicides efficiently eliminate chytrids contamination, they also affect algal growth. The aim of this study was to test the efficiency of chytrids' contamination treatments without affecting algal cells. For this, agricultural fungicides (hexaconazole and copper oxychloride) have been tested at several concentrations and compared with a green decontamination strategy using calcium chloride biomineralization. Hexaconazole caused microalgae bleaching and chytrids bursting even at the lowest tested concentrations (0.01 ppm). At high concentrations, copper-oxychloride, was toxic for H. pluvialis cells, while the chytrids remained resistant to all concentrations of this fungicide. The cell number increased from 1 × 10⁵ ± 100 to 13 × 10⁵ ± 270 cells/ml with 0.25 ppm copper-oxide chloride after 15 days, but later decreased. Treatment with 150 ppm CaCl₂ induced an increase of astaxanthin after 7 days. One week later, algal growth exceeded 22 × 10⁵ cells/ml and the astaxanthin concentration was 22 times higher than the control. After 30 days, the concentration was 3 times higher than the control. Therefore, CaCl₂ at 150 ppm can be used as effective and economical control agent for commercial production of astaxanthin from H. pluvialis.