Cryopreserved Germplasm Case Study: Microalgae

Microalgae are microscopic photosynthetic organisms that play a crucial role in aquatic ecosystems and have diverse applications in biotechnology, aquaculture, and biofuel production. Preserving the genetic diversity of microalgae is essential for research and industrial purposes. Cryopreservation, the process of storing cells at ultra-low temperatures, offers a viable method for long-term preservation. A notable study investigated the cryopreservation of the microalga Scenedesmus sp. using different cryoprotectants to determine optimal conditions for cell viability post-thaw.

In this study, researchers explored the effects of two cryoprotectants—dimethyl sulfoxide (DMSO) and methanol (MET)—at concentrations of 5% and 10% on the cryopreservation efficiency of Scenedesmus sp. The microalgae were subjected to a two-step freezing process: initial cooling to a subzero temperature followed by rapid immersion in liquid nitrogen. Post-thaw viability was assessed using three criteria: no cell damage (NCD), cell damage (CD), and marked lesions (ML). Additionally, flow cytometry was employed to evaluate mitochondrial and cell membrane integrity.

The findings revealed that a 5% concentration of DMSO was most effective in preserving cell viability, with 50% of cells exhibiting no damage (NCD) five days after thawing. In contrast, the control group, which was not exposed to any cryoprotective agents, showed 0% NCD. Flow cytometry analysis indicated minimal damage to the cell membrane and mitochondria (9–10.7%) when 5% DMSO was used, highlighting its protective effect during the freezing and thawing process. While MET at 5% concentration resulted in higher population growth rates post-thaw, it was associated with a higher percentage of cell damage (57%), suggesting that DMSO is more suitable for maintaining cell integrity during cryopreservation.

This study underscores the importance of selecting appropriate cryoprotectants and their concentrations for the successful cryopreservation of microalgae. The use of 5% DMSO emerged as an ideal treatment for Scenedesmus sp., balancing cell viability and growth post-thaw. These findings have significant implications for the long-term storage of microalgal cultures, ensuring the availability of these valuable resources for future research and industrial applications.

In conclusion, the cryopreservation of microalgae like Scenedesmus sp. is a promising approach to maintain their genetic diversity and functional properties over extended periods. Optimizing cryopreservation protocols, including the careful selection of cryoprotectants such as DMSO, is crucial for achieving high post-thaw viability and ensuring the sustainability of microalgal resources for various applications.