Zinc, cadmium, and cobalt interreplacement and relative use efficiencies in the coccolithophore Emiliania huxleyi

Abstract

We investigate the interreplacement of Zn, Cd, and Co in the cosmopolitan coccolithophore Emiliania huxleyi by examining its growth rate, cellular metal quotas, and cellular metal uptake rates under different combinations of Zn, Cd, and Co concentrations in the medium. Co and Zn can fully replace each other, except perhaps for small individual requirements that are met by minute metal concentrations supplied as contaminants. Zn is used at 75% efficiency by E. huxleyi compared with Co. In contrast, Cd can only partially replace Zn or Co and is used at 66% efficiency compared with Co. Up to 50% of the cellular Zn or Co can be replaced by Cd, once the minimum cellular Zn or Co requirement is fulfilled. The limitation by Zn, Cd, and Co and the interreplacement of the three metals occurs over a range of unchelated metal concentrations, 0.2-5 pmol L 21 , that is relevant to surface oceanic waters. Based on our laboratory results and the published metal concentrations in surface oceanic waters, we calculate that interreplacement of Zn, Cd, and Co should occur in regions where Zn is highly depleted.

Nickel limitation and zinc toxicity in a urea‐grown diatom

“…But T. pseudonana is somehow able to maintain a sufficient Ni uptake rate (which is also on the order of a few amol cell 21 d 21 ) down to Ni9 5 0.02 pmol L 21 . Such a very high rate of uptake of a metal at very low concentration, in excess of the supply of unchelated metal by diffusion, has been observed before in phytoplankton (Hudson 1998;Xu et al 2007). A possible though seemingly improbable explanation is that the cells are somehow able to obtain the metal from the EDTA chelate.…”

Elemental Economy

“…In the coccolithophore Emiliania huxleyi , Co may be even more effective than Zn as a cofactor in carbonic anhydrase (Xu et al, 2007). Thus, Co may also support photosynthesis in a Zn-deficient natural environment.…”

Fe Sparing and Fe Recycling Contribute to Increased Superoxide Dismutase Capacity in Iron-Starved Chlamydomonas reinhardtii

“…Examples include replacement of metal cofactors in enzymes, Cd-or Co-containing carbonic anhydrases in place of the usual Zn enzymes, or use of different chemical species, sulfolipids in place of phospholipids in P-deficient bacteria and plants (Benning et al, 1995;Güler et al, 1996;Morel, 2000a, 2000b;Xu et al, 2007;Yu et al, 2002). Mechanisms of Cu sparing in the chloroplast, involving substitution of plastocyanin with cytochrome c 6 and Cu/Zn superoxide dismutase (Cu/ZnSOD) with Fe superoxide dismutase (FeSOD), have been well documented in Cu-deficient algae and plants, respectively (Merchant et al, 2006;Burkhead et al, 2009;Pilon et al, 2011), but the sparing phenomenon has not been as well studied for chloroplast Fe.…”