They are major players in marine food web, as they contribute with ≈40% of global oceanic organic carbon production per year (Allen et al., 2007). The are major contributors in global oxygen production. They are very important in terms of understanding phytoplankton evolution through secondary endosymbiosis as the reason behind their fitness. They live in seawater, freshwater and soil, eitherfreely or in an endosymbiotic relationship. So, it’s time now to know more about their structure and characteristics.complex, species-specific pattern in the structure of the cell-wall, composed chiefly of silica, can be extremely beautiful. Following death of the alga, the empty cell wall may be deposited in the sediments of lakes and oceans and be preserved as a valuable record about past environments and climate changes; as such they are important fossils for the reconstruction of millions of years of the Earth's history.
The map shows surface areas of the world's oceans in which we find high concentrations of nutrients but small amounts of phytoplankton
Mariam rizkallah iron_limitation_in_diatoms
Effect of Iron Limitationon 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 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 Source: reduction size restoration http://www.ucl.ac.uk/GeolSci/mi cropal/diatom.html (auxospores)
Diatoms in the Tree of Life Source: http://chloroplast.ocean.washington.edu/organisms
Diatoms role in the ecosystemand 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 Earths 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-cellresponse 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-cellresponse 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-cellresponse 3/3Down-regulation of Fe-requiring Up-regulation of Fe-economicpathways alternatives- Cell volume reduction and Chl - Alternative shuttling system from concentration reduction chloroplast and cytosol to- Respiration (Fe-dependent electron mitochondria carriers, cytochrome restriction, - Remodeling of the photosynthetic accumulation of TCA intermediates) apparatus (peripheral light-- Photosynthesis (Fv/Fm, quantum harvesting antennas) yield of fluorescence) - Proteome remodeling: glycolysis- Nitrate assimilation and proteolysis of structural- Fe-depended Reactive Oxygen proteins to compensate for Species (ROS) defense (e.g., heme impaired nitrate metabolism in peroxidase and superoxide amino acid synthesis dismutase (SOD)) - Fe-independent ROS defense (e.g., tocopherol and dehydroascorbate) and mitochondrial alternative oxidase (AOX)
Iron limitation and whole-cellresponse Allen et al., 2008
Geoengineering and Ocean iron fertilization (OIF)
Geoengineering and Oceaniron 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)
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