2023 Volume 39 Issue 2 Pages 77-87
Multicellular members of the volvocine green algae represent a unique model lineage in which both sex evolution and multicellularity can be studied experimentally. However, with the exception of Gonium and Astrephomene, methods for cryopreservation of these algae have not been well evaluated. To establish cryopreserved culture strains of the multicellular volvocine algae, we investigated optimal cryopreservation conditions in eight multicellular genera without reproductive cell differentiation, Pandorina, Volvulina, Yamagishiella, Colemanosphaera, Eudorina, Platydorina, Basichlamys, and Tetrabaena. Survival rates by the most probable number (MPN) method were compared among three cryoprotectants [6% N,N-dimethylformamide (DMF), 3% hydroxyacetone, and 5% methanol] after 2 ml cryotubes containing actively growing vegetative colonies mixed with the cryoprotectant were subjected to two-step cooling and freezing in liquid nitrogen. We obtained ≥ 0.1% MPN survival for each of the eight genera when culture samples were subjected to cryogenic treatment with 6% DMF and/or 5% methanol. Using the optimized cryopreservation conditions obtained for each genus, 88 cryopreserved strains belonging to the eight genera were established in the Microbial Culture Collection at the National Institute for Environmental Studies (MCC-NIES).
