Nitrogen (N), phosphorus (P) and Iron (Fe) are important nutrients for phytoplankton, and they are the key limiting nutrients in many marine systems. In the present study, growth and protein expression of marine phytoplankton Prymnesium parvum under different nitrate, phosphate and iron conditions were investigated in order to evaluate whether proteins and their expression level could be used as biomarkers of N, P, and Fe conditions in aquatic systems. The growth of P. parvum increased with the increase of nitrate, phosphate and iron concentrations in the culture medium. Protein expression levels also differed significantly (p < 0.001) for different nitrate, phosphate and iron conditions in the culture medium. The expression level of an 83 kDa protein at 0 and 5 μM nitrate treatments differed significantly (p < 0.001) from those at 20, 30, 50 and 100 μM nitrate treatments, indicating the expression levels of this protein as a biomarker of N status in the culture medium. A 121 kDa protein was up-regulated at phosphate stress conditions ([P] ≤ 1.0 μM), while this protein was not expressed at phosphate replete conditions ([P] ≥ 5 μM). Therefore, the expression of 121 kDa protein in P. parvum is indicative of phosphate deplete condition in aquatic systems. The expression level of a 42 kDa was significantly higher (p < 0.01) at Fe-stress condition ([Fe] = 0.01 μM) than Fe-replete conditions ([Fe] ≥ 0.1 μM). In addition, a new protein of 103 kDa was only expressed under Fe-deplete condition ([Fe] = 0.01 μM). Therefore, the 42 and 103 kDa proteins can be used as a biomarker of Fe-limitation condition of aquatic systems. However, further studies (two dimensional gel electrophoresis and mass spectrometry) are needed to identify and characterize these proteins in P. parvum.
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