Preservation of two microalgae Nannochloropsis oculata and Tetraselmis tetrathele by cooling and freezing

Abstract

Cultures of Nannochloropsis oculata and Tetraselmis tetrathele, previously centrifuged and not centrifuged, were kept in a refrigerator and freezer (without cryoprotector) to test the preservation of these microalgae. N. oculata could be maintained by freezing as well by cooling until 15 months, while T. tetrathele was maintained by these treatments, respectively, for 5 and 7 months. The frozen cultures growth was slower than the growth of cooled ones, and showed a very long lag phase (12 days after a storage of 3 and 5 months, respectively, for N. oculata and T. tetrathele). It was observed that the cell quality of the cooled cultures was preserved, once after its reinoculation these cultures presented the same pattern of population growth as did the cultures which were not stored up anytime. The most simple and efficient method, for both species, was the cooling method for not centrifuged cultures. Nevertheless it should be considered that centrifugation process makes possible the storage of a great number of cells in a small volume.