CRYOPRESERVATION OF DIATOMS

Abstract

Attempts have been made to develop cryopreservation procedures that would allow indefinite storage of freshwater and marine diatoms in culture. Where suitable methods were not achieved, investigation into the cause of freezing injury at the cellular level was made, using cryomicroscopy, salt stress experiments, and electron microscopy.

Of the ten strains of marine diatom tested, eight proved amenable to cryopreservation. Unsatisfactory recovery occurred following freezing in all four strains of freshwater diatom used. At fast (10°C min⁻¹) rates of cooling, freezing injury in Stephanodiscus sp. and Fragilaria crotonensis resulted from intracellular ice formation (IIF). At slow (0.5°C min⁻¹) rates of cooling, IIF was avoided, but freezing injury still occurred, probably due to cytotoxic leakage of vacuolar contents to the cell cytoplasm, as a result of freezing-induced hypertonic stress.