Iron Concentration-Induced Changes in Growth and Biochemical Compositions of Marine Diatom Phaeodactylum tricornutum (Bacillariophyceae)

As long as microalgal growth is not overprolific in the water, marine microalgae are of great benefit to marine ecosystem because they not only form the basis of marine food web, but also consume the greenhouse gas carbon dioxide in the atmosphere during photosynthesis. Sometimes, however, red tides would occur due to the overproliferation or overassemblage of some marine microalgae within a certain short time under some given conditions. The role of iron in the formation of red tides has been a longstanding puzzle before the earlier studies demonstrating that phytoplankton growth in some major nutrient-rich waters was limited by iron deficiency. In order to further investigate the growth characteristics and some important biochemical compositions of marine microalgae induced by iron concentrations, optical density of algal culture, specific growth rate, cell density cell biomass, chlorophyll a and protein of Phaeodaclylum tricornutum were characterized in a laboratory simulative experiment by employing a range of varying iron concentrations including 3.15 mg•L^(-1), 6.30 mg•L^(-1), 9.45 mg•L^(-1), 18.90 mg•L^(-1) and 34.65 mg•L^(-1). Our results indicated that algal growth differed greatly under different iron concentrations set in the present trial. Optical density at 450 nm (OD450) peaked at 0.877 under the iron concentration of 6.30 mg•L^(-1) in the termination of the experiment, and decreased with continually higher iron concentrations. Specific growth rate and cell density increased obviously with the increasing iron concentrations within the range of iron concentration from 3.15 mg•L^(-1) to 9.45 mg•L^(-1), whereas much higher iron concentrations were associated with a decrease in specific growth rate and cell density While, the cell biomass appeared to be concentration-dependent, which was increased gradually over the entire range of iron concentrations. In addition, iron concentration also induced significant changes in the chlorophyll a content and protein content of marine microalga Phaeodaclylum tricornutum. Chlorophyll a content rose under iron concentration ranging from 3.15 mg•L^(-1) to 18.90 mg•L^(-1), but declined under continually higher iron concentrations. Protein content was increased up to 0.153 mg•mL^(-1) by 9.45 mg•L^(-1) iron concentration and it was decreased by much higher iron concentrations, with the manifestly lowest protein content of 0.104 mg•mL^(-1) occurring under the iron concentration of 34.65 mg•L^(-1). The results have provided experimental evidence for the role of iron concentration playing in the marine microalgal proliferation and metabolism, and these findings are particularly important in understanding mechanisms underlying the massive occurrence of red tides around the world, as well as in developing effective strategies for prediction, prevention, and mitigation of red tides.