Interactions among Cu2+, Zn2+, and Mn2+ in controlling cellular Mn, Zn, and growth rate in the coastal alga Chlamydomonas
Limnol. Oceanogr., 43(6), 1998, 1055-1064 | DOI: 10.4319/lo.19126.96.36.1995
ABSTRACT: Culture experiments with the green alga Chlamydomonas sp. in metal ion-buffered media revealed antagonistic interactions between toxic metals (Cu and Zn) and nutrient metals (Zn and Mn) in regulating cellular Mn and Zn uptake and specific growth rate. High levels of ionic Cu2+ and Zn2+ inhibited cellular Mn uptake, and high Cu2+ inhibited Zn uptake rates. These effects were associated with growth rate inhibition at combined conditions of high Zn2+ and low Mn2+ and at high Cu2+ and low Zn2+. Zinc inhibited Mn uptake by competitively blocking Mn binding to a high-affinity Mn uptake system which was under negative feedback regulation. Kinetic modeling suggested that Zn was taken up by this system, and as a result, cellular Zn concentrations increased as external Mn2+ was decreased. Zinc uptake behavior was complex, and in addition to the Mn system, uptake appeared to involve a high-affinity Zn system induced at low Zn2+ and a separate constitutive low-affinity system. High Cu2+ levels inhibited zinc uptake by the high-affinity transport system. Such complex competitive interactions among metals provide important controls on cellular metal accumulation, toxicity, and nutrition.