Proteomics analysis of proteins in green alga Haematococcus lacustris (Chlorophyceae) expressed under combined stress of nitrogen starvation and high irradiance

This study is aimed at identifying the proteins that are up-regulated during astaxanthin accumulation in Haematococcus lacustris. For this H. lacustris cells were cultivated in photobioreactors under normal light irradiance of 40 μE m^-2 s^-1 for 6 days and then induced to accumulate astaxanthin for 3 days further by exposure to continuous high irradiance of 200 μE m^-2 s^-1 with fluorescent lamps as light source after the cells reached the stationary phase in a nitrogen-depleted condition. Under this condition, the average astaxanthin content per cell increased from 91 mg/l up to 406 mg/l after 3 days of induction. The proteomics data from a two-dimensional electrophoretic comparison demonstrated that a combination of nitrogen source depletion and 1 h high light have significantly changed the pattern of protein expression in H. lacustris. A total of 49 protein spots were picked after 1 h of stress induction. They consisted of 13 down-regulated proteins and 36 up-regulated proteins. Fifteen proteins which had highly up-regulated expression were further analyzed by matrix assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS). The results will point toward interesting proteins that can be pursued for further analysis of astaxanthin biosynthesis pathway.