Thanks for entering the discussion, Habib.
You are welcome!
I know that you posted a huge amount of data and links to papers on this topic in my forum a few minutes ago, and it would be great if you could bring it over here (a single cut and paste looses the links).
OK I will give it a try. If links are missing then I will try to correct it ASAP.
Here is one of my posts:
Tatu, Randy & others,
Sorry, it has become a tiny bit loooooooong
Toxicity of (trace) elements depends on the speciation, that is how it is present in the water column.
Free ionic forms will be far more toxic when present in high concentrations than organically bound forms.
The method used for measurement of the elements by Ron also measures besides the free ionic and organically bound forms also particulate forms. E.g. strongly adsorbed on other particles or as the solid oxide or carbonate forms. They will have no direct toxic effect.
Also the data in Ron's study regarding antimony and arsenic is IMO highly suspect. The values are high and are (virtually) the same for all tanks.
If it were known that reef tank inhabinants intentionally release species that control metal concentrations, and that these are not just random happenings but controlled events, then it brings validity that perhaps reef tank inhabitants, either intentionally or unintentionally, detoxify their own environment by releasing metal chelating agents.
O.K. here are some to start with.
The first one is easy to read and is very informative for a large crowd:
Chelation, uptake, and binding of trace metals
The following is the same as above but is the more scientific version:
Extra-cellular iron siderophores: structure and regulation
Another one:
Acquisition and Utilization of Transition Metal
In the above links you will find also other interesting pages on other topics.
The second parts deals with algae:
Intracellular binding: details
The following is from:
http://www.liv.ac.uk/~sn35/Documents/Research_Statement.html
Marine chemical findings
Our measurements are among the first to demonstrate that the biogenic metals (copper, zinc, iron, and cobalt) occur organically complexed in the oceans. Our measurements have shown that organic complexation reactions control the transport of copper, nickel and zinc through estuaries, and that dissolved metal concentrations in estuarine and coastal waters follow dynamic patterns. Unexpectedly anionic elements such as antimony, molybdenum, and uranium were also shown (by CSV) to occur to a significant extent as non-labile species in estuarine waters. A voltammetric study of the geochemistry of platinum in the Indian Ocean conclusively showed that this element has a geochemical behaviour reminiscent to that of manganese in those waters. Our investigations have shown that titanium and aluminium occur as unknown non-labile species, either colloidal or organically complexed, in the oceanic water column. We used our methods to determine the complex stability of sulfide with several metals in seawater, and found that the complex with copper is much more stable than expected.
Probably the most important finding of the last decade in oceanography has been that lack of iron limits oceanic productivity (the Iron Hypothesis). Our finding that iron is organically complexed provides the explanation for its apparent poor availability, and moderates the Iron Hypothesis to a combination of lack of iron and unavailability.
Photochemical effects and the existence of transient species were investigated in the field, showing that the redox chemistry of chromium appears to be controlled both by photochemical and biological processes in the upper water column, causing the presence of significant amounts of chromium(III) where it is thermodynamically unexpected.
We demonstrated that the biologically important folic acid and glutathione occur dissolved in the oceanic water column of the NE Atlantic. Further work has now shown the importance of thiols like glutathione on the chemical speciation of copper suggesting that thiols may well account for at least part of the ligands we see in natural waters.
The complexation reactions likely regulate the rate at which these metals are transferred through the membranes of microorganisms. For this reason we looked at interactions with microorganisms and found that marine algae (the important bloom forming coccolithophore Emiliania huxleyi) release iron-binding ligands in response to iron additions. This work stimulated the use of seawater cultures without modifier additions
Another one:
Nature 400, 858 - 861 (1999)
Competition among marine phytoplankton for different chelated iron species
DAVID A. HUTCHINS*, AMY E. WITTER*, ALISON BUTLERââ"šÂ¬Ã‚ & GEORGE W. LUTHER III*
* College of Marine Studies, University of Delaware, Lewes, Delaware 19958, USA
ââ"šÂ¬Ã‚ Department of Chemistry, University of California, Santa Barbara, California 93106, USA
Correspondence and requests for materials should be addressed to D.A.H. (e-mail:
dahutch@udel.edu).
Dissolved-iron availability plays a critical role in controlling phytoplankton growth in the oceans,. The dissolved iron is overwhelmingly (99%) bound to organic ligands with a very high affinity for iron, but the origin, chemical identity and biological availability of this organically complexed Fe is largely unknown. The release into sea water of complexes that strongly chelate iron could result from the inducible iron-uptake systems of prokaryotes (siderophore complexes) or by processes such as zooplankton-mediated degradation and release of intracellular material (porphyrin complexes). Here we compare the uptake of siderophore- and porphyrin-complexed 55Fe by phytoplankton, using both cultured organisms and natural assemblages. Eukaryotic phytoplankton efficiently assimilate porphyrin-complexed iron, but this iron source is relatively unavailable to prokaryotic picoplankton (cyanobacteria). In contrast, iron bound to a variety of siderophores is relatively more available to cyanobacteria than to eukaryotes, suggesting that the two plankton groups exhibit fundamentally different iron-uptake strategies. Prokaryotes utilize iron complexed to either endogenous or exogenous siderophores, whereas eukaryotes may rely on a ferrireductase system, that preferentially accesses iron chelated by tetradentate porphyrins, rather than by hexadentate siderophores. Competition between prokaryotes and eukaryotes for organically-bound iron may therefore depend on the chemical nature of available iron complexes, with consequences for ecological niche separation, plankton community size-structure and carbon export in low-iron waters.
Citing a few:
Ahner, B. A.. Cornell University,
baa7@cornell.edu
Oleson, J. A.. Cornell University,
jro5@cornell.edu
Slinski, K. M.. Cornell University,
kms32@cornell.edu
GLUTATHIONE CONCENTRATIONS IN FRESHWATER AND MARINE PHYTOPLANKTON
Small organic sulfur compounds play a large role in the intracellular speciation of trace metals in marine and freshwater algae. Glutathione, the principle free thiol in most algae, can complex metals directly or is polymerized enzymatically into metal-binding ligands called phytochelatins. In Emiliana huxleyi, concentrations of g-glutamyl cysteine (a precursor of glutathione) are significantly higher than glutathione which has implications with respect to phytochelatin synthesis. We have examined the effect of prolonged metal exposure on glutathione synthesis in both freshwater and marine algae. We found that deviation from control concentrations of glutathione is highly variable among species, though short-term exposure to Cd stimulates glutathione synthesis in some organisms. Utilizing published and experimentally determined binding constants for glutathione and phytochelatin it is possible to evaluate the probable intracellular speciation of various trace metals such as Cd and Hg. In addition, we are evaluating the use of various metal-specific fluorescent probes to quantify intracellular metal speciation.
From:
http://www.science.plymouth.ac.uk/DEPARTMENTS/Environmental/marchem/marine_chem.htm#Interactions%20between%20Trace%20metal%20and
The uptake and availability of metal species to macrophytes (seaweeds) is currently under investigation within the group. Sensitive electrochemical techniques are used to determine the speciation of metals within culture media containing juvenile stages of seaweeds. These studies have shown that seaweeds release organic material which alters the metal speciation in the culture media. The concentration of this organic material (complexing ligand) released is dependant on both the growth of the the macrophyte and on the concentration of metal, perhaps indicating that these complexing ligands are released in a direct response to the presence of a toxic metal. In parrallel to this, investigations are being undertaken into the intracellular production by algae of specific binding ligands (termed phytochelatins) in response to metals. The distribution and occurrence of phytochelatins is being investigated under laboratory conditions in order to assess the variation in response between different algal species and under variations in temperature and salinity. In addition, concentrations of phytochelatins in natural assemblages of phytoplankton in contaminated and uncontaminated estuaries are being measured. The aim of these studies is to relate phytochelatin production with metal toxicity and to develop a useful biomarker for metal contamination.
Other links:
Lack of phlorotannin induction in the brown seaweed Ascophyllum nodosum in response to increased copper concentrations
Bioavailability of biologically sequestered cadmium and the implications of metal detoxification
From the following link:
ABILITY OF IMMOBILIZED CYANOBACTERIA TO REMOVE
Reports also indicate that carboxyl groups on algal cell biomass are
responsible for binding to various ions (Gardea-Torresdey et al.,1990). Live algae possess
intracellular polyphosphates which participate in metal sequestration, as well as algal extracellular
polysaccharides that serve to chelate or bind metal ions (Zhang and Majidi,1994; Kaplan et
al.,1987; Van Eykelenburg,1978). Strains of Synechocystis spp. have been shown to develop a
thickened calyx when exposed to copper-stressed growth conditions (Gardea-Torresdey et
al.,1996a). Synechococcus sp. PCC 7942 was found to possess a copper-transporting P-type
ATPase in the thylakoid membrane (Bonilla et al.,1995). Synechococcus cedrorum 1191 was
shown to be tolerant to heavy metals and pesticides (Gothalwal and Bisen,1993). Other
investigators have studied the biosorption of heavy metals by algal biomass (Volesky and Holan,
1994; Volesky and Holan, 1995; Volesky and Schiewer, 1997). Such findings show the
possibility of manipulating or overexpressing existing resistance mechanisms and the use of such
organisms to remove harmful metals from the environment.
Other links:
The effect of Fe and Cu on growth and domoic acid production by Pseudo-nitzschia
See page #2 of:
Phytoplankton Physiology and Ecology of Metals