Establishment of a simple method for cryopreservation of the marine diatoms, Chaetoceros and Phaeodactylum

Marine diatoms are important primary producers. Generally, considerable effort is needed to maintain many diatom cultures through periodic sub-inoculation and photoirradiation cultivation procedures. To reduce these endeavors and promote diatom research, this study established a simplified method for the cryopreservation of marine diatoms. Vegetative cells of Chaetoceros tenuissimus , Phaeodactylum tricornutum , and the other species were transferred into a ready-made cryoprotective reagent, CELLBANKER, and directly frozen at − 80 °C and/or in liquid nitrogen (at below − 180 °C) for over two days. Frozen samples were transferred into seawater-based media and cultivated under photoirradiation. Although C . tenuissimus cells were frozen for two years (756 days), certain vegetative cells appeared and grew satisfactorily. Two transgenic types and the wild-type of P . tricornutum were reactivated from the frozen state to maintain the transgenic features. Using the same procedure, we succeeded in cryopreserving Chaetoceros cf. ceratosporus . Our method will be helpful for briefly maintaining diatom cultures and preparing their backup without considerable effort.