Saito, M. A. MIT / WHOI Joint Program - Chemical Oceanography,
Moffett, J. A. Woods Hole Oceanographic Institution,
Chisholm, S. W. Massachusetts Institute of Technology,

We hypothesize that Prochlorococcus has a cobalt uptake mechanism utilizing biogenic cobalt specific ligands -- i.e. cobalophores -- which are conditioning the culture media. Evidence for this hypothesis, derived from cobalt limitation experiments with strain SS120 in EDTA and NTA media, includes: 1) lag phases that are inversely proportional to total cobalt concentration in the media, 2) deviance from the free ion model for Co2+ uptake, 3) increases in growth rate with time, consistent with first order production of ligands with respect to cell number, 4) alleviation of cobalt limitation and increases in cobalt uptake by addition of spent media, 5) an increase in cobalt limitation by nickel additions but not by zinc additions, consistent with the fact that most strong cobalt ligands are also strong nickel ligands. The cultures were not axenic, thus we cannot yet rule out the potential role of heterotrophic bacteria in ligand production. Given the low total cobalt concentrations in the oligotrophic oceans (1-2 orders less than iron) and the dominance of Prochlorococcus in subtropical regions, it is possible that this hypothesized cobalophore uptake mechanism is a source of the cobalt complexation measured in the Sargasso Sea (Moffett and Saito, ASLO 1999).
Day: Thursday, Feb. 4
Time: 04:15 - 04:30pm
Location: Sweeney Center
Code: SS28TH0415S