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

Exploring iron-organic ligands and the microbial utilization of iron in the ocean. Distribution of nitrate in surface waters. H igh N utrient L ow C hlorophyll regions ( HNLC ). Horn et al., EPSL , 2011. The Biological Roles of Iron. Respiration. Photosynthesis. Oxidative stress.

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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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