Microalgal cell immobilization for the long-term storage of the marine diatom Haslea ostrearia

To preserve the characteristics of the marine diatom Haslea ostrearia during long term storage, particularly size and shape, the algal cells were immobilized in alginate beads and stored at 4 ^∘C at reduced irradiance up to 4 months. Two clones of different size (Ho34, 63 μm and Ho40, 78 μm) were studied. With Ho34, a 10.4% decrease of the size was shown after 120 days, by using the conventional storage management, while it did not exceed 2.2% with immobilized cells. Consequently, H. ostrearia would have auxosporulated after 9 months compared to 52 months. At the same time, the rate of distortion (aberrant valve structure) free Ho34 cells reached 86% while no distorted immobilized cells were observed. Chorophyll content in cells showed that all the cells were alive up to 60 days and after this time cells immobilized in the core of the beads most probably suffered from the poor light diffusion. Culturability of the immobilized cells was tested immediately after their immobilization and after 60 and 120 days of storage. The delay (at least 5) before immobilized cells released from the beads decreased with the time of storage, because of the embrittlement of the beads during the storage. Once in fresh medium, the cells actively multiplied. We concluded that immobilization strongly slowed down the decrease in frustule size with time and allowed the storage of concentrated and calibrated inocula which could be inoculated directly in liquid culture medium without needing to dissolve the beads.