Abstract
Phaeocystis antarctica is an abundant phytoplankton species in the Southern Ocean, where growth is frequently limited by iron and light. Being able to grow under low iron conditions is essential to the species’ success, but there have been hints that this ability differs among clones. Here, we compare the growth, cell size and chlorophyll a concentrations of four P. antarctica clones cultured under different iron and light conditions. Iron was provided either as unchelated iron (Fe′) or bound to the bacterial siderophore desferrioxamine B, representing, respectively, the most and least bioavailable forms of iron which phytoplankton encounter in the marine environment. The growth rate data demonstrate that the clones vary in their ability to grow using organically bound iron, and that this ability is not related to their ability to grow at low inorganic iron concentrations. These results are consistent at low and high light. Physiologically, only three of the four clones shrink or decrease the concentration of chlorophyll a in response to iron limitation, and only one clone decreases colony formation. Together, our data show that P. antarctica clones 1) respond to the same degree of iron limitation using different acclimation strategies, and 2) vary in their ability to grow under the same external iron and light conditions. This physiological diversity is surprisingly large for isolates of a single phytoplankton species.
Highlights
Phaeocystis antarctica is an abundant bloom-forming phytoplankton species in the Southern Ocean, where it plays a pivotal role in the marine carbon and sulfur cycles [1, 2]
Growth in iron limiting media differs among clones The P. antarctica clones were grown in two low iron media, high ethylene diamine tetraacetic acid (EDTA) and high desferrioxamine B (DFB) (Fig 1, Table 1)
In the high EDTA medium, clone W51 experiences the lowest degree of iron limitation, followed by clones AA1 and SX9
Summary
Phaeocystis antarctica is an abundant bloom-forming phytoplankton species in the Southern Ocean, where it plays a pivotal role in the marine carbon and sulfur cycles [1, 2]. We systematically grew three P. antarctica clones under different iron and light conditions and monitored their growth rates, cell size, chlorophyll a concentrations and colony formation. Three P. antarctica clones were acclimated to growth media with different concentrations of EDTA and DFB, two iron binding ligands whose chemistry within the artificial growth medium is well studied [9, 10].
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