The effect of salinity on the growth and photosynthesis of a novel psychrophilic and halotolerant Chlamydomonas species from Antarctica

The effect of salt on the green alga Chlamydomonas raudensis Ettl (UWO241) was investigated. This physchrophilic alga was discovered in a permanently ice-covered lake in Antarctica in the beginning of the 90's and was then classified as Chlamydomonas subcaudata. A phylogenetic study by Pocock et al. (2004) revealed that this alga was in fact a C.raudensis species. The latter type species was first discovered in an alpine meadow in Czech republic and kept in the SAG culture collection as strain number 49.72. The aim of this study was to use the potential high sensitivity of the extremophile to understand the effect of salinity on photosynthesis of phytoplankton in the oceans, where microalgae play a key role in the carbon cycle on earth. It has to be determined if global warming, which is leading to the melting of the north ice cap and thus to the dilution of the North Atlantic ocean will have a negative impact on algal populations. This study lays the foundations for a larger study, which focuses on the compounds released by these green algae that could potentially counteract the greenhouse effect by increasing the albedo on earth. The study includes a comparison of C. raudensis UWO241 (psychrophilic strain) with C. raudensis SAG 49.72 (mesophilic strain) and the model organism C.reinhardtii, (mesophile). Also none of the latter two are known to be halotolerant. The growth kinetics of the three species has been investigated at different salinities ranging from 2 µM to 200 mM NaCl and between 24°C and 28°C for the mesophiles and from 2 µM to 850 mM at 8°C for the psychrophile. All algae were grown under 20 μmol quanta m-2 s-1 irradiance. Furthermore, chlorophyll a fluorescence was used to determine the stress level caused by the salt on the three species.