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Exploring iron-organic ligands and the microbial utilization of iron in the ocean

Explore the distribution of iron and organic ligands in oceanic waters and their impact on microbial utilization of iron. Learn about the role of iron in respiration, photosynthesis, and other biological processes. Discover the importance of iron as an essential micronutrient and its effect on phytoplankton growth. Delve into the complex world of marine iron ligands and their role in acquiring iron from seawater.

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Exploring iron-organic ligands and the microbial utilization of iron in the ocean

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  1. Exploring iron-organic ligands and the microbial utilization of iron in the ocean Agouron 2015 Lecture 3

  2. Distribution of nitrate in surface waters High Nutrient Low Chlorophyll regions (HNLC) Agouron 2015 Lecture 3 Horn et al., EPSL, 2011

  3. The Biological Roles of Iron Respiration Photosynthesis Oxidative stress Nitrogen fixation DNA replication Agouron 2015 Lecture 3

  4. Iron as an essential, limiting micronutrient John Martin of Moss Landing Marine Lab noticed during a study of the N. Pacific HNLC region that chlorophyll increased after an Asian dust event Agouron 2015 Lecture 3

  5. 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fe (nm kg -1) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Depth (km) Agouron 2015 Lecture 3 K. Coale et al.

  6. 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 Fe (nm kg -1) 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Fe + H2O +Organic Matter (ligands, “L”)  Fe’(H2O)+ FeL +Fe(O)(OH) + others Depth (km) Agouron 2015 Lecture 3 K. Coale et al.

  7. Fe cell requirements for Synechococcus and Prochlorococcus Percent maximum growth rate Anne Thompson Ph.D. Thesis, 2009 Agouron 2015 Lecture 3

  8. Iron Limitation: Model of Small Phytoplankton Growth Limitation Agouron 2015 Lecture 3 Moore et al., Global Biogeochemical Cycles, 2004

  9. Iron Limitation: Model of Small Phytoplankton Growth Limitation “Give me a half tanker of iron and I will give you an ice age.” –John Martin Agouron 2015 Lecture 3 Moore et al., Global Biogeochemical Cycles, 2004

  10. Agouron 2015 Lecture 3

  11. Artificial Ocean Iron Fertilization Agouron 2015 Lecture 3

  12. Qualitative Nature of the Ligand Pool: Electrochemistry 1. Add Fe 2. Compete with known ligand Natural ligands vs. SA 3. Measure with electrochemistry Current Randie Bundy Agouron 2015 Lecture 3 Potential

  13. Marine Iron Ligands • Concentration of Fe ligands nearly always exceeds dissolved Fe. • Conditional stability constant LogKFeL between 10 -13. • Suggests that >99% of dissolved Fe is complexed. Agouron 2015 Lecture 3 Boye et al., Marine Chemistry, 2006

  14. How do microbes acquire iron from seawater ? Fe (III) -Ligand S Ligand S-Fe (III) light S + Fe(II) Fe (II) S-Fe (III) Siderophore (S) Fe (III) Agouron 2015 Lecture 3

  15. Examples of siderophore structures from marine bacteria Agouron 2015 Lecture 3 From JM Gauglitz, 2011

  16. Agouron 2015 Lecture 3

  17. Steps for investigating metal ligands • Step 1 – DOM extraction from sample • Step 2 – Find metals associated with DOM • Step 3 – Characterize these compounds. Agouron 2015 Lecture 3

  18. Step 1: Solid Phase Extraction • Simplify matrix and preconcentrate organics Agouron 2015 Lecture 3

  19. Step 2: LC-ICPMS j ICP-MS h M-L M+ f i l a k d g b c e Agouron 2015 Lecture 3

  20. Siderophore variability across an eddy Sea Surface Height 56Fe LC-ICPMS: Station 2 56Fe LC-ICPMS: Station 2 Agouron 2015 Lecture 3

  21. Siderophore variability across an eddy Sea Surface Height 56Fe LC-ICPMS: Station 3 Agouron 2015 Lecture 3

  22. Siderophore variability across an eddy Sea Surface Height 56Fe LC-ICPMS: Station 4 Agouron 2015 Lecture 3

  23. Step 3 ESI-MS ESIMS ESI-MS spectra are extremely complex! M-L M-L+ Agouron 2015 Lecture 3

  24. Search for Fe isotope pattern Δmass = 1.995 Δintensity = 0.06 56Fe 54Fe Agouron 2015 Lecture 3

  25. Agouron 2015 Lecture 3

  26. Rapid and efficient discovery of siderophores In the cyanobacterium Synechococcus 7702 Agouron 2015 Lecture 3

  27. MS/MS Agouron 2015 Lecture 3

  28. Siderophores from Alteromonas 56Fe LC-ICPMS Identified as marinobactins 54Fe and 56Fe LC-ESIMS Marinobactin A’ Marinobactin A Marinobactin B Marinobactin C Marinobactin D Marinobactin E Agouron 2015 Lecture 3

  29. Siderophore variability across an eddy Sea Surface Height 56Fe LC-ICPMS: Station 4 Amphibactins New siderophore m/z 709.364 Agouron 2015 Lecture 3

  30. Siderophores in the GEOTRACES Program Agouron 2015 Lecture 3

  31. Subtropical North Pacific (Hoe-Phor) 2nd separation on collected fractions Agouron 2015 Lecture 3

  32. Subtropical North Pacific (Hoe-Phor) Agouron 2015 Lecture 3

  33. Future plans – field experimental work 1.) Add << 57Fe citrate 2.) Incubate 3.) Measure Fe Ratio Natural abundance 56Fe-Ligand + 57Fe 57Fe-Ligand + 56Fe 56Fe (57Fe+56Fe) kd Equilibrium Sample Dissociation of Fe-Ligand (kd) determines 56Fe loss rate Incubation Time Agouron 2015 Lecture 3

  34. 57Fe isotope exchange Amphibactins 56Fe (57Fe+56Fe) Unknown ‘Humics’ Incubation Time (Days) [Total Dissolved] = 120pM Fe [Humics] ~ 30 pM Fe [Siderophores] ~ 7 pM Fe Time (min) Agouron 2015 Lecture 3

  35. The experiment we really really want to do 1) Label natural ligands 2) Spike seawater with labeled ligands 3) Flow sort cells 56Fe-Ligand + 55Fe 55Fe-Ligand + 56Fe 4) Measure where The iron-55 is Agouron 2015 Lecture 3

  36. Future plans – other metals, P and S ‘Biomolecules’ appear to have a preference for one metal over others. • Ill-defined ‘humics’ seem to bind all metals. Agouron 2015 Lecture 3 Retention Time (min)

  37. Agouron 2015 Lecture 3

  38. With thanks to: Rene Boiteau Randie Bundy and- Jess Fitzsimmons Ed Boyle Jim Moffett Eric Webb Penny Chisholm NSF & CMORE Rene Randie Agouron 2015 Lecture 3

  39. Each ESI-MS scan is complex Agouron 2015 Lecture 3

  40. Distribution of nitrate in surface waters Agouron 2015 Lecture 3 Horn et al., EPSL, 2011

  41. Exploring microbial iron acquisition in the ocean. Agouron 2015 Lecture 3

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