Effect of Iron Limitation on DiatomsMariam RizkallahBiotechnology Master’s ProgramThe American University in Cairo
Outline• Diatoms, their structure, applications, and role in the
ecosystem• Iron limitation and whole-cell response (Allen et al.,
2008)• Ocean fertilization attempts (Smetacek et al., 2012)• Co-limitation of diatoms by iron and silica (Brzezinski et
al., 2011)
Diatoms diversity
Source: http://tolweb.org/images/Diatoms/21810
Diatoms structure and life cycle• Unicellular photosynthetic
“microalgae”• Inhabitants of aquatic
systems: seawater, freshwater and soil, freely or in an endosymbiotic relationship
• Of siliceous skeleton (frustule)• Between 20-200 microns in
diameter or length• Cell division (epitheca as
parent frustule) size reduction size restoration (auxospores)
Source: http://www.ucl.ac.uk/GeolSci/micropal/diatom.html
Diatoms in the Tree of Life
Source: http://chloroplast.ocean.washington.edu/organisms
Diatoms role in the ecosystem and applications• Diatoms and the global carbon cycle:- Primary producers in the aquatic food web [e.g., they
contribute with ≈40% of global oceanic organic carbon production per year (Allen et al., 2007)]
- Major contributors in global oxygen production
• Diatoms as indicators of the Earth's history:- Indicator of the past environments and climate changes
through tracking the sediments of the empty silica cell wall deposited after their death
- Living diatoms optimal growth conditions vs. that of extinct ones as way of palaeoenvironmental reconstruction
• Diatoms nanotechnology (Bradbury, 2004)
Iron limitation and whole-cell response
Iron limitation and whole-cell response 1/3• Observation:- Diatoms-dominating blooms after Fe-repletion in high nutrient low chlorophyll (HNLC) regions - HNLC regions: subarctic Pacific, equatorial Pacific, and Southern Oceans and North Atlantic)
Source: http://www.polartrec.com/expeditions/seawater-property-changes-in-the-southern-ocean/journals/2011-03-21
Iron limitation and whole-cell response 2/3• One of the species studied:- Phaeodactylum tricornutum: highly tolerant to Fe-limitation
• Methods:- Growth conditions: Cultures grown in Fe-limited media, followed by Fe
addition- Physiological measurements: Photosynthetic fitness, cell diameter and
volume, Fe reductase assay and chlorophyll (Chl) concentration- Gene expression profiling: Expressed Sequence Tags (ESTs )libraries,
partial genome microarray, Real Time quantitative Reverse transcription Polymerase Chain Reaction (qRT-PCR)
- Comparative genomics : Mapping ESTs to predicted proteins encoded by P. tricornutum genome and across lineages
- Metabolites extraction: Gas chromatography-mass spectroscopy (GC-MS)
Iron limitation and whole-cell response 3/3
Down-regulation of Fe-requiring pathways
Up-regulation of Fe-economic alternatives
- Cell volume reduction and Chl concentration reduction
- Respiration (Fe-dependent electron carriers, cytochrome restriction, accumulation of TCA intermediates)
- Photosynthesis (Fv/Fm, quantum yield of fluorescence)
- Nitrate assimilation- Fe-depended Reactive Oxygen
Species (ROS) defense (e.g., heme peroxidase and superoxide dismutase (SOD))
- Alternative shuttling system from chloroplast and cytosol to mitochondria
- Remodeling of the photosynthetic apparatus (peripheral light-harvesting antennas)
- Proteome remodeling: glycolysis and proteolysis of structural proteins to compensate for impaired nitrate metabolism in amino acid synthesis
- Fe-independent ROS defense (e.g., tocopherol and dehydroascorbate) and mitochondrial alternative oxidase (AOX)
Iron limitation and whole-cell response
Allen et al., 2008
Geoengineering and Ocean iron fertilization (OIF)
Geoengineering and Ocean iron fertilization (OIF)• The European Iron Fertilization Experiment (EIFEX):- Enhancement of CO2 sequestration from the atmosphere via
eliminating the phytoplankton growth limiting factor, Fe- Testing the “iron hypothesis” in the Southern Ocean as a
typical HNLC region (bloom were observed via satellite upon continental and volcanic iron addition)
- Measurements at different depths were taken, pre-, during and post-fertilization
- Chemical analysis of Chl, particulate organic carbon (POC), nitrogen (PON), phosphate (POP) and biogenic silica (BSi) concentrations (ratios indicated diatoms domination)
Co-limitation by iron and silica
Co-limitation by iron and silica
Concluding remarks• Diatoms have a major role in carbon cycle and oxygen
production.• Iron is crucial for growth, photosynthesis, respiration and ROS
response in diatoms.• However, diatoms show adaptation to iron limitation.• Ocean fertilization is a way for geoengineering depending on
iron hypothesis.• Iron may be the limiting factor for diatoms growth, however,
silica may be a limiting factor for diatoms silicification and division.
References• Allen, A. E., Laroche, J., Maheswari, U., Lommer, M., Schauer, N., Lopez, P. J.,
Finazzi, G., et al. (2008). Whole-cell response of the pennate diatom Phaeodactylum tricornutum to iron starvation. Proceedings of the National Academy of Sciences of the United States of America, 105(30), 10438–43
• Smetacek, V., Klaas, C., Strass, V. H., Assmy, P., Montresor, M., Cisewski, B., Savoye, N., et al. (2012). Deep carbon export from a Southern Ocean iron-fertilized diatom bloom. Nature, 487(7407), 313–319. doi:10.1038/nature11229
• Brzezinski, M. A., Baines, S. B., Balch, W. M., Beucher, C. P., Chai, F., Dugdale, R. C., Krause, J. W., et al. (2011). Co-limitation of diatoms by iron and silicic acid in the equatorial Pacific. Deep Sea Research Part II: Topical Studies in Oceanography, 58(3-4), 493–511. doi:10.1016/j.dsr2.2010.08.005
• The Friedrich Hustedt Diatom Study Centre: http://www.awi.de/index.php?id=2366&L=0
• Diatoms and climate change – The use of diatom analysis in reconstructing Late Holocene climate for Kigoma Region, Tanzania: http://www.geo.arizona.edu/nyanza/pdf/Meeker.pdf