Impact of procedural steps and cryopreservation agents in the cryopreservation of chlorophyte microalgae

The maintenance of traditional microalgae collections based on liquid and solid media is labour intensive, costly and subject to contamination and genetic drift. Cryopreservation is therefore the method of choice for the maintenance of microalgae culture collections, but success is limited for many species. Although the mechanisms underlying cryopreservation are understood in general, many technical variations are present in the literature and the impact of these are not always elaborated. This study describes two-step cryopreservation processes in which 3 microalgae strains representing different cell sizes were subjected to various experimental approaches to cryopreservation, the aim being to investigate mechanistic factors affecting cell viability. Sucrose and dimethyl sulfoxide (DMSO) were used as cryoprotectants. They were found to have a synergistic effect in the recovery of cryopreserved samples of many algal strains, with 6.5% being the optimum DMSO concentration. The effect of sucrose was shown to be due to improved cell survival and recovery after thawing by comparing the effect of sucrose on cell viability before or after cryopreservation. Additional factors with a beneficial effect on recovery were the elimination of centrifugation steps (minimizing cell damage), the reduction of cell concentration (which is proposed to reduce the generation of toxic cell wall components) and the use of low light levels during the recovery phase (proposed to reduce photooxidative damage). The use of the best conditions for each of these variables yielded an improved protocol which allowed the recovery and subsequent improved culture viability of a further 16 randomly chosen microalgae strains. These isolates included species from Chlorellaceae, Palmellaceae, Tetrasporaceae, Palmellopsis, Scenedesmaceae and Chlamydomonadaceae that differed greatly in cell diameter (3-50 mu m), a variable that can affect cryopreservation success. The collective improvement of each of these parameters yielded a cryopreservation protocol that can be applied to a broad range of microalgae

Advantages and Applications of Cryopreservation in Fisheries Science

Cryopreservation is a long-term storage technique to preserve the biological material without deterioration for extended period of time at least several thousands of years. The ability to preserve and store both maternal and paternal gametes provides a reliable source of fish genetic material for scientific and aquaculture purposes as well as for conservation of biodiversity. Successful cryopreservation of fish sperm have been achieved for more than 200 fish species and many fish species have been adequated for the purpose of cryobanking. Cryopreservation of fish embryo is not viable, mainly because of the same limitations as in fish oocytes, i.e., high chilling sensitivity and low membrane permeability. However, cryopreservation of isolated embryonic cells is another option for preserving both maternal and paternal genome. In this paper, an overview of the current state of aquatic species is followed by a discussion on the sperm, embryos, oocytes and embryonic cells - blastomeres