פרופ' יעלה שקד

Biogeochemical cycling, redox dynamics and chemical speciation of trace metals in aquatic ecosystems. Trace metal nutrition and toxicity to phytoplankton. Phytoplankton's extra-cellular enzyme activity - geochemical and environmental significance. Photochemical cycling of iron and reactive oxygen species in natural waters. Biological production and detoxification of reactive oxygen species

 

 

Iron Availability to Phytoplankton

Iron is quantitatively the most important micronutrient metal for phytoplankton in aquatic ecosystems. As such, the concentrations and availability of iron for phytoplankton can influence the ocean chemistry, major nutrients and carbon cycling, particulate matter transport, and gas exchange with the atmosphere. While different phytoplankton groups may possess different iron utilization mechanisms it is widely accepted that the chemical forms of iron present in the ocean are not readily accessible by phytoplankton. We seek to better understand the chemical and biological parameters that determine the bio-availability of organically bound iron and colloidal iron to marine algae. We study natural phytoplankton populations and laboratory cultures using synthetic compounds and colloids as well as ambient dust.

 

Recent publications in the area:

• Lis, H., Shaked, Y., Kranzler, C., Keren, N. and F. M. M Morel. 2015. Iron bioavailability to phytoplankton - an empirical approach. The ISME Journal 9: 1003-1013 doi:10.1038/ismej.2014.19
• Lis, H., Kranzler, C., Keren, N. and Y. Shaked. 2015. A comparative study of iron uptake rates and mechanisms amongst marine and fresh water cyanobacteria, Life, (special issue “cynaobacteria: Ecology, Physiology and Genetics”). http://www.mdpi.com/2075-1729/5/1/841.
•  Kranzler, C., Kessler, N., Keren, N. and Y. Shaked. 2016. Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: insights into the bioavailability of particulate iron. Environmental Microbiology and Environmental Microbiology Reports. doi:10.1111/1462-2920.13496

Schoffman H, Lis H, Shaked Y and N. Keren .2016. Iron–Nutrient Interactions within Phytoplankton. Frontiers in Plant Sciences. 7(1223). doi: 10.3389/fpls.2016.01223

Dust as a nutrient source to marine microogranosms: the role of microbial interactions in dust dissolution

Dust and aerosols deposition into nutrient-poor ocean surface water are of considerate importance for supplying phytoplankton and bacteria essential nutrients such as iron (Fe) and phosphorus (P). However, since dust quickly settles to depth, most of the Fe and P remain as stable minerals in the dust and are not released into the water as soluble bioavailable nutrients. Struggling to sequester Fe and P from dust, phytoplankton and bacteria are forced to apply various mechanisms to retain the dust at the ocean surface and accelerate its dissolution rate. Research in the Shaked’s group revealed that the globally important, N₂ fixing, cynaobacterium, Trichodesmium can actively capture and transport dust to its colony core, as well as increase dust-Fe solubility. Currently, we further investigate the ability of Trichodesmium to extract nutrients from dust assisted by their resident bacteria, thus exploring a new type of phytoplankton-bacteria interaction.

 

Recent publications in the area:

• Rubin, M., Berman-Frank, I., and Y. Shaked. 2011. Dust- and mineral-iron utilization by the marine dinitrogen-fixer Trichodesmium. Nature Geosciences 4(8): 529–534

 

 

Dynamics of dms/p in the gulf of Aqaba – open waters and coral reefs

The organosulfur compounds Dimethylsulfoniopropionate (DMSP) and Dimethylsulfide (DMS) are of great environmental, biogeochemical, physiological and ecological interest. In the reef water, DMSP is considered an important carbon and sulfur source for coral associated bacteria and serve as a chemo-attractant of various organisms to corals and reefs. For chemo-sensing to occur, chemical gradients from the reef to the surrounding water must persist on a spatial scale relevant to the organism size and motility. In the last years we have been studying the dynamics of DMS/P in the Eilat coral reef, asking if the reef is indeed a DMS/P source, or rather a sink. We are investigating the distribution and residence times of these compounds on coral surfaces and their surroundings hoping to better understand the ecological, biochemical and biogeochemical roles of DMS/P in coral reefs and other coastal environments.

 

Recent publications in the area:

• Amrani, A., Said-Ahmad, W., Shaked, Y. and R. P. Kiene. 2013. Sulfur isotope homogeneity of oceanic DMSP and DMS. Proceedings of the National Academy of Sciences USA 110(46): 18413-18418.

 

1. Berman-Frank, I., Cullen, J. T., Shaked, Y., Sherrell, R. M. and Falkowski, P.G., 2001. Iron availability, cellular iron-quotas and nitrogen fixation in Trichodesmium, Limnology and Oceanography, 46(6): 1249-1260.
2. Shaked, Y., Erel, Y., Sukenik, A., 2002.  Phytoplankton mediated redox cycle of iron in the epilimnion of Lake Kinneret, Environmental Science and Technology, 36: 460-467.
3. Shaked, Y., Erel, Y., Sukenik, A., 2004. The biogeochemical cycle of iron and associated elements in Lake Kinneret, Geochemica et Cosmochemica Acta, 68(7): 1439-1451.*
4. Shaked, Y., Kutska, A. B., Morel, F. M. M., and Erel, Y., 2004.  Simultaneous determination of iron reduction and uptake by Phytoplankton, Limnology and Oceanography Methods 2: 137-145.
5. Shaked, Y., Kutska, A. B., and Morel, F. M. M., 2005. A general kinetic model for iron acquisition by eukaryotic phytoplankton, Limnology and Oceanography, 50(3): 872-882.
6. Kutska, A. B., Shaked, Y., Milligan, A. J., King W. D., and Morel, F. M. M. 2005. Extracellular production of superoxide by marine diatoms: contrasting implications for Fe redox chemistry and bioavailability, Limnology and Oceanography, 50(4): 1172-1180.
7. Shaked, Y., Xu, Y., Leblanc, K., Morel, F. M. M., 2006. Zinc availability and alkaline phosphatase activity in Emiliania huxleyi: Implications for Zn-P co-limitation in the ocean, Limnology and Oceanography, 51(1): 299-309.
8. Xu, Y., Wahlund, T. M, Feng, L., Shaked, Y., Morel, F. M. M. 2006. A novel alkaline phosphatase in the coccolithophore Emiliania huxleyi and its regulation by phosphorus, Journal of Phycology, 42(4): 835-844.
9. Shcolnick, S., Y. Shaked, N. Keren. 2007. A role for mrgA, a DPS family protein, in the internal transport of Fe in the cyanobacterium Synechocystis sp. PCC6803, Biochimica et Biophysica Acta, 814-819.
10.  Xu, Y., D. Tang, Y. Shaked, and F. M. M. Morel.  2007. Zinc, cadmium, and cobalt inter-replacement and relative use efficiencies in the coccolithophore Emiliania huxleyi. Limnology and Oceanography, 52(5): 2294-2305.
11. Castruita, M., L. A. Elmegreen, Y. Shaked, E. I. Stiefel, and F. M. M. Morel. 2007. Comparison of the kinetics of iron release from a marine (Trichodesmium Erythraeum) Dps protein and mammalian ferritin in the presence and absence of ligands. Journal of Inorganic Biochemistry, 101 (11-12) 1686-1691.  
12. Morel, F. M. M., Kutska, A. B., and Y. Shaked. 2008. The role of unchelated Fe in the iron nutrition of phytoplankton, Limnology and Oceanography. 53(1): 400-404.
13. Castruita, M., Shaked, Y., Elmegreen, L. A ., Stiefel, E. I., and F. M. M. Morel. 2008. Availability of iron from iron storage proteins to marine phytoplankton, Limnology and Oceanography. 53(3): 890-899.
14. Y. Shaked. 2008. Iron redox dynamics in the surface waters of the Gulf of Aqaba, Red Sea. Geochemica et Cosmochemica Acta, 72(6): 1540-1554.
15. Lis, H. and Y. Shaked. 2009. Probing the bioavailability of organically bound iron – a case study in the Synechococcus rich waters of the Gulf of Aqaba. Aquatic Microbial Ecology 56(2-3):241-253.
16. Shaked, Y. Harris, R., and N. Klein-Kedem. 2010. Hydrogen Peroxide Photocycling in the Gulf of Aqaba, Red Sea. Environmental Science and Technology 44(9): 3238–3244.
17. Saragosti, E.,  Katsir, A., Tchernov, D. and Y. Shaked. 2010. Extracellular Production and Degradation of Superoxide in the Coral Stylophora pistillata and Cultured Symbiodinium. PLoS ONE 5(9): e12508. doi:10.1371/journal.pone.0012508
18. Rubin, M., Berman-Frank, I., and Y. Shaked. 2011. Dust- and mineral-iron utilization by the marine dinitrogen-fixer Trichodesmium. Nature Geosciences 4(8): 529–534.
19. 19). Kranzler, C., Lis, H., Shaked, Y., and N. Keren. 2011. The role of reduction in iron uptake processes in a unicellular, planktonic cyanobacterium. Environmental Microbiology 13: 2990–2999. doi: 10.1111/j.1462-2920.2011.02572.x
20. Shaked, Y and H. Lis. 2012. Disassembling iron availability to phytoplankton. Frontiers in Microbiological Chemistry 3: 123. doi: 10.3389/fmicb.2012.00123
21. Meeder, E., Mackey, K. R. M., Paytan, A., Shaked, Y., Iluz, D., Stambler, N., Rivlin, T., Post, A.F., and B. Lazar. 2012. Nitrite dynamics in the open ocean—clues from seasonal and diurnal variations. Marine Ecology Progress Series 453:11-26.
22. Shaked, Y and A. Rose. 2013. Seas of Superoxide. Science 430: 1176-1177.
23. Amrani, A., Said-Ahmad, W., Shaked, Y. and R. P. Kiene. 2013. Sulfur isotope homogeneity of oceanic DMSP and DMS. Proceedings of the National Academy of Sciences USA 110(46): 18413-18418.
24. Shaked, Y and R. Armoza-Zvuloni. 2013. Dynamics of hydrogen peroxide in a coral reef: sources and sinks. Journal of Geophysical Research: Biogeosciences 118: 1793–1801. doi:10.1002/2013JG002483
25. Kranzler, C., Lis, H., Finkel, O. M., Schmetterer G., Shaked, Y., and N. Keren. 2014. Coordinated Transporter Activity Shapes High Affinity Iron Acquisition in Cyanobacteria. The ISME Journal 8: 409–417. doi:10.1038/ismej.2013
26. Armoza-Zvoluni, R and Y. Shaked. 2014. Release of H₂O₂ and antioxidants by the coral Stylophora pistillata to its external milieu. Biogeosciences 11(17): 4587-4598.

27. ​Horwitz, R., Borell, E. M., Fine, M., and Y. Shaked. 2014. Trace element profiles of the sea anemone Anemonia viridis living nearby a natural CO₂ vent. PeerJ 2: e538.

28. Lis, H., Shaked, Y., Kranzler, C., Keren, N. and F. M. M Morel. 2015. Iron bioavailability to phytoplankton - an empirical approach. The ISME Journal 9: 1003-1013 doi:10.1038/ismej.2014.199

29. Lis, H., Kranzler, C., Keren, N. and Y. Shaked. 2015. A comparative study of iron uptake rates and mechanisms amongst marine and fresh water cyanobacteria, Life, (special issue “cynaobacteria: Ecology, Physiology and Genetics”). http://www.mdpi.com/2075-1729/5/1/841.

30. Armoza-Zvuloni R., Schneider A., Sher D. and Y Shaked. 2016. Rapid Hydrogen Peroxide release from the coral Stylophora pistillata during feeding and in response to chemical and physical stimuli. Scientific Reports 6, #21000

31. Armoza-Zvuloni R., Schneider A., and Y Shaked. 2016. Rapid release of Hydrogen Peroxide during coral-bacteria interactions. Frontiers in Marine Sciences 3 (1142), doi: 10.3389/fmars.2016.00124

32. Kranzler, C., Kessler, N., Keren, N. and Y. Shaked. 2016. Enhanced ferrihydrite dissolution by a unicellular, planktonic cyanobacterium: insights into the bioavailability of particulate iron. Environmental Microbiology and Environmental Microbiology Reports. doi:10.1111/1462-2920.13496

33. Schoffman H, Lis H, Shaked Y and N. Keren .2016. Iron–Nutrient Interactions within Phytoplankton. Frontiers in Plant Sciences. 7(1223). doi: 10.3389/fpls.2016.01223

34. Torfstein A, Teutsch N, Tirosh O, Shaked Y, Rivlin T, Zipori A, Stein M, Lazar B, and Y. Erel. 2017. Chemical characterization of atmospheric dust from a weekly time series in the north Red Sea between 2006 and 2010, Geochimica et Cosmochimica Acta, 211; 373-393.

 

Education

1997 – 2002    Ph.D. Environmental and Earth Sciences, The Hebrew University, Jerusalem, Israel.  Dissertation: Iron redox dynamics and

                         biogeochemical   

​                         cycling in the epilimnion of Lake Kinneret. Co-advisors: Drs. Yigal Erel and Assaf Sukenik.

1994 – 1997     B.Sc. Environmental and Earth Sciences, The Hebrew University, Jerusalem, Israel.  cum laude.

 

Employment

2015 – present  Associate Professor (tenured), Interuniversity Institute for Marine Sciences, and Institute of Earth Sciences, Hebrew University.

2010 – 2015      Senior Lecturer (tenured), Interuniversity Institute for Marine Sciences, and Institute of Earth Sciences, Hebrew University.

2005 – 2010      Lecturer, Interuniversity Institute for Marine Sciences, and Institute of Earth   Sciences, Hebrew University.

2002 – 2005      Postdoctoral Research Associate, Princeton Environmental Institute, Department of Geosciences, Princeton University, with Prof.

                          Francois M. M. Morel.  Theme: Kinetics and mechanisms of trace metals and major nutrients acquisition by marine phytoplankton

 

Awards

2006                 Yakov Livland Award, The Hebrew University

2002 –2004     Bikura fellowship for postdoctoral research. National Academy of Sciences, the Israel Science Foundation

2000 – 2002    Ben-Nun fellowship for doctoral research. Israel Limnology and Oceanography Research Ltd.  

2002                 Student Poster Award, Faculty of Sciences, Hebrew University

2002                 Student Poster Award, ASLO summer meeting

1996 & 1997   The Carples Award, The Hebrew University.

 

 

STUDENT MENTORING

MSc

2015 – 2017         Uria Tal

2011 – 2013         Yaron Halevy

2010 – 2013         Guy Levi (with Nava Moran)

2008 – 2010         Chana Kranzler (with Nir Keren continued to a pHd)

2007 – 2009         Eldad Saragosti (with Dan Tchernov),

2007 – 2009         Maxim Rubin (with Ilana Berman-Frank)

2007 – 2009         Hagar Lis (continued to a pHd)

PhD

2017 – present    Siyuan Wang

2013 – 2018         Nivi Kessler (with Nir Keren)

2010 – 2016         Chana Kranzler (with Nir Keren)

2009 – 2015         Hagar Lis (with Nir Keren)

2005 – 2012         Efrat Meeder (with Boaz Lazar)

Post-Doc

2018 – present    Dr. Yitzhak Jacobson

2018 – 2019         Dr. Meri Eichner (with Dirk DeBaar)

2014 – present    Dr. Subhajit Basu

2012 – 2014         Dr. Rachel Armoza-Zvoluni

 

GRANTS

2018-2021     Israel Science Foundation (ISF) – National Science Foundation China (NSFC) research

                         grant (with Dalin Shi).  Primary Production in the Changing Ocean - Effects of Ocean

                         Acidification on Trichodesmium metabolism and iron utilization from dust.

2018-2020     FICUS Award for research at EMSL and JGI National US facilities (with R. Boiteau, R.

                        Stuart and M. Gledhill). Interactive mechanisms of mineral dissolution by a microbial   

                         consortia.

2018-2021      German-Israeli Foundation for Scientific Research and Development (GIF) research grant (with M. Gledhill and E. Achterberg). Dust iron utilization by natural Trichodesmium colonies.

2015-2019       Israel Science Foundation (ISF) research grant. Bioavailability of particulate iron to   planktonic cyanobacteria.

2011-2015       Israel Science Foundation (ISF) research grant. Dynamics of Reactive Oxygen Species in Coral Reefs – Sources, Sinks and Roles.

2009 – 2013    United States – Israel Binational Science Foundation (BSF) research grant (with Francois. M. M. Morel). Iron bioavailability to phytoplankton: do different taxa share similar uptake mechanisms?

2011                 Ring Foundation for Environmental Studies research grant (with N. Keren). Iron acquisition strategies of open ocean phytoplankton.

2009                 Israel Science Foundation (ISF), institutional basic equipment grant. In situ measuring and sampling system for oceanography (leading PI).

2007 – 2011    Israel Science Foundation (ISF) research grant. Atmospheric iron inputs to the ocean:   Can phytoplankton significantly affect aerosol Fe solubility and redox chemistry?

2007 – 2009    United States – Israel Binational Science Foundation (BSF) research grant (with F. M. M. Morel). Availability of organically bound iron to marine phytoplankton.

2006                 Ring Foundation for Environmental Studies research grant (with N. Keren). Linking phytoplankton's iron homeostasis and iron recycling in the ocean.

 

 

RESEARCH AND TEACHING EXPERIENCE

2016– 2017       Visiting Professor at the University of British Columbia, Canada (sabbatical)

2005 – present  Hebrew University's Earth Sciences Inst, and IUI. Courses – Biological Oceanography, Introduction to the ecosystem of     the Gulf of Aqaba, Marine biogeochemistry, Nutrient biogeochemistry and uptake, Research Methods in Oceanography,  Practical     Oceanography.

Summer 2004   Princeton University, Quest- teacher training program, Guest lecturer.

1997 – 2002      The Hebrew University of Jerusalem, Teaching and Research Assistance.

Summer 2000   IMCS, Rutgers University, Research Internship with Dr. Paul Falkowski.    Theme: Iron availability, cellular iron-quotas and nitrogen fixation of the marine cyanobacteria Trichodesmium.

Summer 1999   NOAA laboratory, North Carolina, Research Internship with Dr. William Sunda.     Theme: Trace metals-phytoplankton interactions in Chesapeake Bay

1996 - 1997       The Hebrew University of Jerusalem, Research Assistance.    Subject: Radon measurements in springs along the African-Syrian Rift.

Summer 1996   Cranfield University, UK, Research Internship with Dr. Simon Parsons.  Theme: Prevention of limescale formation in cooling towers.

 

OTHER PROFESSIONAL ACTIVITIES

2017- present   Head of the Oceanography Program, Hebrew Univ

2017- present   Member of GEOTRACES Scientific Steering Committee

2016– present  Full member SCOR working group: Iron Model Intercomparison Project (FeMIP)

2013 – 2016      Member of the organizing committee of the Israel Association for Aquatic Sciences

 

 

 

 

 

 

 

Current Members

Siyuan Wang, Ph.D. Student
2017-today:   

Nivi Kessler, Ph.D. Student
2013-today:   (with Nir Keren)

Subhajit Basu, Postdoc
2015-today:   

Murielle Dray, Technician
2005-today:   

Past Members

Yaron Halevy, M.Sc. Student
2011-2013:   

Eldad Saragosti, M.Sc. Student
2007-2009:   (with Dan Tchernov)

Maxim Rubin, M.Sc. Student, Dr.
2007-2009:   (with Ilana Berman-Frank)

Chana Kranzler, Ph.D. Student, Dr.
2010-2016:   (with Nir Keren)

Hagar Lis, Ph.D. Student
2009-2015:   (with Nir Keren)

Efrat Meeder, Ph.D. Student
2005-2012:   (with Boaz Lazar)

Rachel Armoza-Zvuloni, Postdoc
2012-2016:   

Guy Levi, M.Sc. Student
2010-2013:   (with Nava Moran)

כתבה על המחקר של פרופ שקד שהתפרסם לאחרונה כחלק מסדרת כתבות על נשים במדע  

https://www.news1.co.il/Archive/0024-D-133211-00.html

כתבה נוספת הכוללת מחקר של פרופ יעלה שקד

https://www.knowablemagazine.org/article/physical-world/2019/ocean-iron-fertilization

 

:New publication highlighting GEOTRACES

https://www.geotraces.org/phytoplankton-bioavailability/