1. Nitrogen-fixing Soil Bacteria and their response to Trace Elements
Garrett Baird ‘17
PEI Internship, Morel Lab
Research Adviser: Oliver Baars

2. Goals
Main goal was to grow Azotobacter Vinelandii and Azotobacter Chroococcum under different conditions with varying Tungsten and Boron concentrations in order to determine toxicity.
Monitored growth by measuring Optical Density at 620 nm.
Tracked siderophore production using Liquid Chromatography Mass Spectroscopy (LC-MS) .
Also tracked intracellular metal concentration using Inductively Coupled Plasma Mass Spectroscopy (ICP-MS).

3. Example LC-MS graph

4. Azotobacter Vinelandii (AV)
Nitrogen-fixing diazotroph that can fix nitrogen aerobically
Can make three different nitrogenases: Molybdenum, Vanadium, and Fe-only
Has siderophores with catechol moieties that bind oxyanions and iron well
Main siderophores: Vibrioferrin, DHBA, Aminochelin, Azotochelin, and Protochelin
Goal was to grow AV under different Tungsten and Boron conditions and see how they responded

5. AV Siderophores
Vibrioferrin
DHBA

6. Azotobacter Chroococcum (AC)
Nitrogen-fixing diazotroph that can fix nitrogen aerobically
Has siderophores with hydroxamate functional groups that bind well to iron but poorly to oxyanions.
Main siderophores: Vibrioferrin and various Amphibactins
Goal was to grow AC under different Tungsten and Boron conditions and see how they responded in comparison to AV
Vibrioferrin
Example Amphibactin

7. Example Result

8. Example Result

9. Example Result

10. Example Result
ICP-MS Results (concentrations in ppb)

11. Summary of Results
Did similar experiments for AV with different W concentrations and AC with different W and B concentrations.
Noticeable difference in growth for AV at 10 mM B and 100 μM W. For AC, 10 mM B and 100 mM W.
High concentrations of W is one of the few conditions where AC actually grows better than AV.
For AV, very little Vibrioferrin is produced at high W (>1 mM) and high B (10 mM) concentrations.