Cooperative heavy-metal
detoxification by P. aeruginosa
Siobhán O’Brien, Adela Luján & Angus Buckling
College of Life and Environmental Sciences, University of Exeter Cornwall Campus, UK
Email: s.obrien@exeter.ac.uk
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
Siderophore production:
A model system for studying cooperation
Fe2+
West SA & Buckling A. 2003 Proc.R.Soc.Lond.B 270:37 – 44.
Griffin AS et al. Nature. 430 :1024 – 1027
West SA et al 2007 Annu. Rev. Ecol. Evol.Syst.38:53 – 77
S.OBrien@exeter.ac.uk
Braud et al. 2010. Environ Microbiol. 2: 419 – 425
Microbial communities- Cambridge
28 October 2014
Our Questions
Part 1
Can siderophore
production in
response to copper
toxicity be a
cooperative trait?
S.OBrien@exeter.ac.uk
Part 2
Can toxic copper
environments select
for rapid evolution of
cheats?
Microbial communities- Cambridge
Part 3
How is cheat fitness
affected by the soil
microbial
community?
28 October 2014
How do we determine if a behaviour is altruistic?
There is a benefit to the recipient
Do cooperators outcompete cheats
when grown alone?
Ch Ch
Ch
The behaviour itself is costly
Do cheats outcompete cooperators
in competition?
WT WT
WTWT
WT
WT
WTCh
Ch
Ch
WT
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
1. Is heavy metal detoxification by siderophores a cooperative
trait?
Wt
Ch
1:1
Copper
Sulfate
(X12)
6mM CuSO4
Strains:
Wt: PAO1
Ch:PAO1ΔPvdΔPch
Cheat
Cooperator
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
1. Is heavy metal detoxification by siderophores a cooperative
trait?
0.8
0.6
0.4
0.2
alone
in competition
0.0
Relative fitness of cheat
1.0
1. Do cooperators do
better than cheats
when grown alone in
toxic environments? ✔
Toxic Cu
1. Do cheats outcompete
cooperators in
competition in toxic
environments? ✔
Control (Fe)
Treatment
Cheat relative fitness ~ metal treatment: conditions: F1,89 =207.89, p < 0.001)
O’Brien, Hodgson & Buckling. Social Evolution of toxic Metal Bioremediation in P. aeruginosa. 2014.Proc.R.Soc.Lond.B 281(1787)
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
1. Is heavy metal detoxification by siderophores a cooperative
trait?
Experimental evolution (approx. 105 generations)
WT
Copper
WT
X12
Iron
Frequency of cheats
S.OBrien@exeter.ac.uk
Total siderophore
(pyoverdine) production
Microbial communities- Cambridge
28 October 2014
Toxic Cu
300
150
200
250
***
100
0.3
0.2
0.0
0.1
Cheat frequency
0.4
Population level sideorphore production
(absorbance/OD)
350
0.5
1. Is heavy metal detoxification by siderophores a cooperative
Conclusion:
trait?
Copper detoxification is a social trait that actively selects for the
***
evolution of social “cheats”.
Control (Fe)
Treatment
Toxic Cu
Control (Fe)
Treatment
O’Brien, Hodgson & Buckling. Social Evolution of toxic Metal Bioremediation in P. aeruginosa. 2014.Proc.R.Soc.Lond.B 281(1787)
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
Our Questions
Part 1
Can siderophore
production in
response to copper
toxicity be a
cooperative trait?
S.OBrien@exeter.ac.uk
Part 2
Can toxic copper
environments select
for rapid evolution of
cheats?
Microbial communities- Cambridge
Part 3
How is cheat fitness
affected by the soil
microbial
community?
28 October 2014
How is cheat fitness affected by the presence of the soil
microbial community?
Cheat
(species 2)
Cooperator
(species 1)
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
How is cheat fitness affected by the presence of the soil
microbial community?
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
How is cheat fitness affected by the presence of the soil
microbial community?
Monoculture
only
+community
Comm.
copper only
- Comm.
+ Comm.
copper and community
(cheat fitness~ copper*community, p=0.03). Error bars
represent +/-SE
S.OBrien@exeter.ac.uk
1.5
1.0
Cheat relative fitness (W)
-Comm.
no copper/no community
+Cu
+Cu
0.0
+Cu
0.5
Cheat relative fitness (w)
1.2
1.0
0.8
+Cu
0.0
Cheat relative fitness (W)
0.6
0.4
0.2
Cheat relative fitness (w)
2.0
1.4
Co-culture
no copper/no community
-Comm.
community only
+ Comm.
copper only
- Comm.
copper and community
+ Comm.
(cheat fitness~ copper, p=0.01). Error bars represent +/SE
Microbial communities- Cambridge
28 October 2014
Summary
•Heavy metal detoxification by
bacterial siderophores is a
cooperative behaviour, that selects
for rapid evolution of social ‘cheats’
•In toxic copper soil, cheat fitness is
increased in the presence of the
community, but in monoculture
conditions only.
•Cheats cannot ‘invade’ populations
of cooperators in soil as they can in
synthetic media.
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
Thanks for listening!
•
•
•
•
•
•
Angus Buckling
Dave Hodgson
Adela Luján
Florian Bayer
Elze Hesse
Eleanor Van Veen
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
How is cheat fitness affected by the presence of the
soil microbial community?
Cu2+
Cu2+
Cu2+
Cheat
Cu2+
Cu2+
Cooperator
Cu2+
Cu2+
Cu2+
Cu2+
Cu2+
Cheat
(species 2)
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
How is cheat fitness affected by the presence of the
soil microbial community?
Monoculture
1.5
1.0
Cheat relative fitness (W)
0.0
0.5
Cheat relative fitness (w)
1.2
1.0
0.8
Cheat relative fitness (W)
0.6
0.4
0.0
0.2
Cheat relative fitness (w)
2.0
1.4
Co-culture
no copper/no community
community only
copper only
copper and community
(cheat fitness~ copper*community, p=0.03). Error bars
represent +/-SE
Iron-limited
Toxic copper
- community
<1***
<1***
+ community
=1
=1
no copper/no community
community only
copper only
copper and community
(cheat fitness~ copper, p=0.01). Error bars represent +/SE
Iron-limited
Toxic copper
- community
<1*
=1
+ community
=1
=1
Siderophore production:
A model system for studying cooperation
transportation
Fe2
+ Fe2+




Fe3
+
Fe3
Mineral/protein
Fe3
+
+
siderophore
producer
West SA, Buckling A. 2003 Cooperation, virulence and siderophore production in bacterial parasites. Proc.R.Soc.Lond.B 270:37 – 44.
Griffin AS, West SA, Buckling A. 2004 Cooperation and competition in pathogenic bacteria. Nature. 430 :1024 – 1027
West SA, Diggle SP, Buckling A, Gardner A, Griffin AS. 2007 The social lives of microbes. Annu. Rev. Ecol. Evol.Syst.38:53 – 77.
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014
Siderophores bind other heavy metals too…
Cu2+
✗

Cu2+
Cu2+
Cu2+
Cu2+
Cu2+
Cu2+
Cu2+
Cu2+
2+
siderophore Cu
producer
…but don’t take them into the cell
Braud A, Geoffroy V, Hoegy F, Mislin GLA, Schalk IJ. 2010 Presence of the siderophores pyoverdine and pyochelin in the extracellular medium
reduces toxic metal accumulation in Pseudomonas aeruginosa and increases bacterial metal tolerance. Environ Microbiol. 2: 419 – 425
S.OBrien@exeter.ac.uk
Microbial communities- Cambridge
28 October 2014