Dataset Information

Nonspecific uptake and homeostasis drive the oceanic cadmium cycle.

ABSTRACT: The global marine distributions of Cd and phosphate are closely correlated, which has led to Cd being considered as a marine micronutrient, despite its toxicity to life. The explanation for this nutrient-like behavior is unknown because there is only one identified biochemical function for Cd, an unusual Cd/Zn carbonic anhydrase. Recent developments in Cd isotope mass spectrometry have revealed that Cd uptake by phytoplankton causes isotopic fractionation in the open ocean and in culture. Here we investigate the physiochemical pathways that fractionate Cd isotopes by performing subcellular Cd isotope analysis on genetically modified microorganisms. We find that expression of the Cd/Zn carbonic anhydrase makes no difference to the Cd isotope composition of whole cells. Instead, a large proportion of the Cd is partitioned into cell membranes with a similar direction and magnitude of Cd isotopic fractionation to that seen in surface seawater. This observation is well explained if Cd is mistakenly imported with other divalent metals and subsequently managed by binding within the cell to avoid toxicity. This process may apply to other divalent metals, whereby nonspecific uptake and subsequent homeostasis may contribute to elemental and isotopic distributions in seawater, even for elements commonly considered as micronutrients.

SUBMITTER: Horner TJ

PROVIDER: S-EPMC3574901 | biostudies-other | 2013 Feb

REPOSITORIES: biostudies-other

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Nonspecific uptake and homeostasis drive the oceanic cadmium cycle.

Horner Tristan J TJ Lee Renee B Y RB Henderson Gideon M GM Rickaby Rosalind E M RE

Proceedings of the National Academy of Sciences of the United States of America 20130129 7

The global marine distributions of Cd and phosphate are closely correlated, which has led to Cd being considered as a marine micronutrient, despite its toxicity to life. The explanation for this nutrient-like behavior is unknown because there is only one identified biochemical function for Cd, an unusual Cd/Zn carbonic anhydrase. Recent developments in Cd isotope mass spectrometry have revealed that Cd uptake by phytoplankton causes isotopic fractionation in the open ocean and in culture. Here w ...[more]

PMID: 23362377

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Project description:Synechococcus sp. WH 8102 is a motile marine cyanobacterium isolated originally from the Sargasso Sea. To test the response of this organism to cadmium (Cd), generally considered a toxin, cultures were grown in a matrix of high and low zinc (Zn) and phosphate (PO4 (3-)) and were then exposed to an addition of 4.4 pM free Cd(2+) at mid-log phase and harvested after 24 h. Whereas Zn and PO4 (3-) had little effect on overall growth rates, in the final 24 h of the experiment three growth effects were noticed: (i) low PO4 (3-) treatments showed increased growth rates relative to high PO4 (3-) treatments, (ii) the Zn/high PO4 (3-) treatment appeared to enter stationary phase, and (iii) Cd increased growth rates further in both the low PO4 (3-) and Zn treatments. Global proteomic analysis revealed that: (i) Zn appeared to be critical to the PO4 (3-) response in this organism, (ii) bacterial metallothionein (SmtA) appears correlated with PO4 (3-) stress-associated proteins, (iii) Cd has the greatest influence on the proteome at low PO4 (3-) and Zn, (iv) Zn buffered the effects of Cd, and (v) in the presence of both replete PO4 (3-) and added Cd the proteome showed little response to the presence of Zn. Similar trends in alkaline phosphate (ALP) and SmtA suggest the possibility of a Zn supply system to provide Zn to ALP that involves SmtA. In addition, proteome results were consistent with a previous transcriptome study of PO4 (3-) stress (with replete Zn) in this organism, including the greater relative abundance of ALP (PhoA), ABC phosphate binding protein (PstS) and other proteins. Yet with no Zn in this proteome experiment the PO4 (3-) response was quite different including the greater relative abundance of five hypothetical proteins with no increase in PhoA or PstS, suggesting that Zn nutritional levels are connected to the PO4 (3-) response in this cyanobacterium. Alternate ALP PhoX (Ca) was found to be a low abundance protein, suggesting that PhoA (Zn, Mg) may be more environmentally relevant than PhoX.

Dataset Information

Nonspecific uptake and homeostasis drive the oceanic cadmium cycle.

Publications

Nonspecific uptake and homeostasis drive the oceanic cadmium cycle.

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