Microalgal cryopreservation using Dimethyl Sulfoxide (Me2SO) coupled with two freezing protocols : influence on the fatty acid profile

International audienceProcedures for determining the optimal pre-freezing protocol for cryo-preservation of microalgae are discussed. Three algal species were used (Chlorella vulgaris, Isochrysis galbana and Dunaliella salina) and cryo-stored using two different methods: the slow cooling and the fast freezing. In the slow cooling, each algae batch was treated with or without cryo-protectant (dimethyl sulfoxide: Me2SO 5% v/v). After 20 min at 4 degrees C, the midi-straws were filled and cooled slowly (1.5 degrees C min(-1)) to -140 degrees C, by a programmable freezer (Digitcool-IMV), before putting them directly into liquid nitrogen. Fast freezing was performed with 10% or 15% Me2SO prior to plunging into liquid nitrogen. The three algal species followed the same re-growth pattern as that of the controls. The post-thawed viability with Me2SO was good for all the selected algae (C. vulgaris > 95%, I. galbana and D. sauna > 70% of the control), applying the slow cooling. The post-thawed viability without Me2SO was 60% for I. galbana, 52% for D. salina and 33% for C. vulgaris. Fast freezing was not suitable for cryo-storage of I. galbana but gave good post-thawing viability for D. salina (70%). The decrease in fatty acid content of the cryo-stored algae was influenced by the temperature. The rapid decrease in temperature induced by fast freezing can explain the low level of fatty acid content of the three cryo-stored algae. Fatty acid profiles show that the nutritional values of the three cryo-stored micro-algae were not significantly affected especially when treated with slow cooling protocols

Micro-algal cryopreservation using Dimethyl Sulfoxide (Me2SO) coupled with two freezing protocols: influence on the fatty acid profile

Procedures for determining the optimal pre-freezing protocol for cryo-preservation of microalgae are discussed. Three algal species were used (Chlorella vulgaris, Isochrysis galbana and Dunaliella salina) and cryo-stored using two different methods: the slow cooling and the fast freezing. In the slow cooling, each algae batch was treated with or without cryo-protectant (dimethyl sulfoxide: Me2SO 5% v/v). After 20 min at 4 degrees C, the midi-straws were filled and cooled slowly (1.5 degrees C min(-1)) to -140 degrees C, by a programmable freezer (Digitcool-IMV), before putting them directly into liquid nitrogen. Fast freezing was performed with 10% or 15% Me2SO prior to plunging into liquid nitrogen. The three algal species followed the same re-growth pattern as that of the controls. The post-thawed viability with Me2SO was good for all the selected algae (C. vulgaris > 95%, I. galbana and D. sauna > 70% of the control), applying the slow cooling. The post-thawed viability without Me2SO was 60% for I. galbana, 52% for D. salina and 33% for C. vulgaris. Fast freezing was not suitable for cryo-storage of I. galbana but gave good post-thawing viability for D. salina (70%). The decrease in fatty acid content of the cryo-stored algae was influenced by the temperature. The rapid decrease in temperature induced by fast freezing can explain the low level of fatty acid content of the three cryo-stored algae. Fatty acid profiles show that the nutritional values of the three cryo-stored micro-algae were not significantly affected especially when treated with slow cooling protocols

Biochemical adaptation of phytoplankton to salinity and nutrient gradients in a coastal solar saltern, Tunisia

International audienceThe distribution of protein and carbohydrate concentrations of the particulate matter (size fraction: 0.45–160 mm) was studied, from 22 January 2003 to 02 December 2003, in three ponds of increasing salinity in the Sfax solar saltern (Tunisia). The coupling of N/P: DIN (DIN ¼ NO2 þ NO3 þ NH4þ) to DIP (DIP¼ PO4 3 ) with P/C: protein/carbohydrates ratios along salinity gradient allowed the discrimination of three types of ecosystems. Pond A1 (mean salinity: 45.0 5.4) having marine characteristics showed enhanced P/C ratios during a diatom bloom. N/P and P/C ratios were closely coupled throughout the sampling period, suggesting that the nutritional status is important in determining the seasonal change in the phytoplankton community in pond A1. In pond A16 (mean salinity: 78.7 8.8), despite the high nitrate load, P/C ratios were overall lower than in pond A1. This may be explained by the fact that dinoflagellates, which were the most abundant phytoplankton in pond A16 might be strict heterotrophs and/or mixotrophs, and so they may have not contributed strongly to anabolic processes. Also, N/P and P/C ratios were uncoupled, suggesting that cells in pond A16 were stressed due to the increased salinity caused by water evaporation, and so cells synthesized reserve products such as carbohydrates. In pond M2 (mean salinity: 189.0 13.8), P/C levels were higher than those recorded in either pond A1 or A16. N/P and P/C were more coupled than in pond A16. Species in the hypersaline pond seemed paradoxally less stressed than in pond A16, suggesting that salt-tolerant extremophile species overcome hypersaline constraints and react metabolically by synthesizing carbohydrates and proteins