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.