Nitrogen-fixing Soil Bacteria and their
response to Trace Elements
Garrett Baird ‘17
PEI Internship, Morel Lab
Research Adviser: Oliver Baars
Goals
 Main goal was to grow AzotobacterVinelandii 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).
Example LC-MS graph
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
AV Siderophores
Vibrioferrin
DHBA
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
Example Result
Example Result
Example Result
Example Result
 ICP-MS Results (concentrations in ppb)
AV, Control t22
AV, Control t25
AV, Control t41
AV, 1 mM B added t22
AV, 1 mM B added t25
AV, 1 mM B added t41
AV, 10 mM B added t22
AV, 10 mM B added t25
AV, 10 mM B added t41
B10(MR)
B11(MR)
Fe56(MR) Mo98(MR) W184(MR) OD
-2.205
-0.801
7.681
1.174
-0.064
-2.150
-1.208
19.094
1.744
-0.084
-0.534
0.376
90.810
2.619
-0.098
-1.474
-0.640
7.472
1.149
-0.076
-1.409
-0.420
19.387
1.922
-0.090
1.200
2.036
80.667
2.017
-0.077
-1.249
-0.103
18.543
1.537
-0.080
-2.352
-1.256
8.284
1.473
-0.091
-1.469
-0.447
48.792
2.398
-0.099
0.375
0.724
1.799
0.369
0.651
1.774
0.238
0.29
1.38
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.