Intraspecific variability among Chilean strains of the astaxanthin-producing microalga Haematococcus pluvialis (Chlorophyta): an opportunity for its genetic improvement by simple selection

The unicellular green alga Haematococcus pluvialis accumulates large quantities of astaxanthin, a highly valuable carotenoid pigment in the aquaculture, food, and pharmaceutical industries. Biological diversity within a species with a biotechnological interest allows applying strain selection procedures avoiding genetic manipulation. The aim of this study was to determine growth and carotenogenic capacity among 13 strains isolated from a latitudinal range throughout south-central and southern Chile, in order to know their biological diversity and biotechnological potential. Strains were isolated from rain pools located in public squares and cemeteries of the cities: Concepcion, Valdivia, Osorno, Puerto Varas, and Castro. All the Chilean strains were more carotenogenic than the reference strain Steptoe. Physiological attributes differed greatly among the strains. Principal component analysis (PCA) of growth and carotenogenesis parameters grouped the strains into four groups, two of them composed by only one strain (CCM-UdeC-038 and CCM-UdeC-039). These latter strains were also the most carotenogenic ones, being strain CCM-UdeC-039 the one that accumulated the highest amount of astaxanthin (7 mg astaxanthin L-1 culture) associated to the highest total carotenoid content (1.1 % by dry biomass) and carotenoids/chlorophyll ratio (2.6). These results demonstrate that a great physiological diversity exists at intraspecific level in H. pluvialis (even among strains coming from the same geographical origin), which allows performing genetic improvement by means of simple selection of new strains from nature. Further research will be focused on finding out the culture conditions that optimize the astaxanthin production of the most promising strains.