ATOPFe - NEW EXPERIMENTS ON Fe AND Cu BIOAVAILABILITY: NEW SCENARIOS IN THE FUTURE OCEANS BY M. MALDONADO
I
have enjoyed tremendously my stay in the QUIMA lab of Profs. Magdalena Santana-Casiano
and Melchor Gonzalez-Davila this April (2018). I have learnt so much from
everyone! I send my warmest thank you to all members of the QUIMA lab,
especially to Aridane Gonzalez and Carolina Santana Gonzalez, as well as Profs.
Melchor Gonzalez and Magdalena Santana. I
have furthered my knowledge and experience with competitive ligand exchange-adsorptive cathodic stripping voltammetry
(CLE-ACSV), using the BASi Controlled Growth Mercury Electrodes
(CGME) voltammeter. We have focused on measuring organic complexation of Cu, as
well as designing and executing experiments to measure the kinetics of Fe and
Cu adsorption to phytoplankton cell surfaces. With this work we aim to
establish the density, kinetic constants and conditional stability constants of
metal transporters specific for Cu and Fe at the cell surface of phytoplankton.
This month, as a start, we used the diatoms, Phaeodactylum tricornutum and Thalassiosira
oceanica as model phytoplankton. These diatoms have distinct strategies to
acquire Cu and Fe, and respond physiologically different to Cu and/or Fe
limitation (Maldonado and Price 2001; Allen et al. 2008; Shi et al. 2010;
Lommer et al. 2012; Santana-Casiano et al. 2014; Guo et al. 2015; McQuaid et
al. 2018). We hope to determine how
lowering dissolved Cu or Fe concentrations in seawater affect their cellular Cu
and Fe transport and homeostasis mechanisms. Within the next year, we will also
study the effects of ocean acidification on trace metal bioavailability. This
work will elucidate what will control the bioavailability of Fe and Cu to
marine phytoplankton in our oceans in the near future. This is part of the
recently funded project to Profs. Santana-Casiano and Gonzalez-Davila, entitled
“Effects of ocean acidification, temperature and organic matter on Fe(II)
persistence in the Atlantic Ocean; ATOPFe”. This project is timely, as the
newly established Global Ocean Acidification Observing Network (GOA-ON) aims to
improve our understanding of a)
the global ocean acidification conditions, as well as the ecosystem response to
ocean acidification. In addition, this network aims to acquire and exchange the
data and knowledge necessary to optimize the modeling of ocean acidification
and its impacts.
High
atmospheric CO2 levels are not only resulting in a warmer global
climate, but are also profoundly changing the chemistry of our oceans. As the
ocean absorbs ~30% of our anthropogenic CO2 emission, its surface waters
are becoming more acidic. The acidification of our oceans is expected
to significantly affect trace metal bioavailability by changing a) the inorganic
metal chemistry, b) the metal binding capacity of the organic ligands, and c)
the kinetic parameters of trace metal transport in phytoplankton. So far, only
a handful of studies have investigated the effects of ocean acidification on
trace metal availability, focusing mainly on Fe. In collaboration, with Profs. Santana-Casiano
and Gonzalez-Davila, we will examine the effects of ocean acidification on the
concentration and speciation of the bioactive trace element Fe and Cu. We
hypothesized that ocean acidification will decrease Fe availability and
increase Cu toxicity to phytoplankton, which would ultimately result in a
decrease in primary productivity in marine surface waters. As the pH decreases
it is harder for the cell to eject the H+ they will send out at the
same time as the electron that is reducing the organically bound Fe.
Major forms of Fe in seawater and depiction
of a eukaryotic microalgal cell illustrating various Fe uptake mechanisms. From
A. Marchetti and M. T. Maldonado, “Iron” in “The Physiology of
microalgae” by B. Borowitzka, M.A., Beardall, J. Raven J., Eds.; W.D.P.
Stewart, California, 2016.
Proposed model of Cu acquisition & homeostasis
in marine diatoms
Guo, J., B. Green, and M.T. Maldonado.
2015. Sequence Analysis and Gene Expression of Potential Components of Copper
Transport and Homeostasis in Thalassiosira pseudonana. Protist 166:
58–77.
References cited
Allen, AE, et al. 2008. Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation. Proceedings of the National Academy of Sciences 105 (30), 10438-10443
Guo, J., BR Green, MT Maldonado. 2015. Sequence analysis and gene expression of potential components of copper transport and homeostasis in Thalassiosira pseudonana. Protist 166 (1), 58-7
Lommer, M., et al. 2012. Genome and low-iron response of an oceanic diatom adapted to chronic iron limitation. Genome Biology 201213:R66
Maldonado, MT, NM Price. 2001. Reduction and transport of organically bound iron by Thalassiosira oceanica (Bacillariophyceae). Journal of Phycology 37 (2), 298-310
McQuaid, JB, et al 2018 Carbonate-sensitive phytotransferrin controls high-affinity iron uptake in diatoms Nature 555 (7697), 534
Santana-Casiano, J.M., M. González-Dávila, A.G. González, M. Rico, A. López, A. Martel. 2014.
Characterization of phenolic exudates from Phaeodactylum tricornutum and their effects on the chemistry of Fe(II)–Fe(III). Marine Chemistry 158 (2014) 10–16.
Shi D, Xu Y, Hopkinson BM, Morel FM. 2010. Effect of ocean acidification on iron availability to marine phytoplankton. Science. 2010 : 327(5966):676-9