mariam rizkallah iron_limitation_in_diatoms
DESCRIPTION
A 12-min presentation in graduate seminar about iron limitation and diatoms and ocean fertilization.TRANSCRIPT
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