Low concentrations of PAHs induce
tolerance in nitrifying bacteria
J Fredrik Lindgren*1, Ida-Maja Hassellöv1,
Hanna Landquist1, Ingela Dahllöf2
1Shipping
and Marine Technology, Chalmers University of Technology
2Biology and Environmental Sciences, Gothenburg University
WoW III – Gothenburg
2015-10-13
Outline
Background
PICT
Study
Results
Conclusions
Small spills - Low concentrations of oil
Benthic habitats
Polycyclic Aromatic Hydrocarbons (PAHs)
•
•
•
•
•
Sub-lethal effects
Carcinogenic effects
Lowered fecundity/reproduction
Lowered resistance to other stress
Depressed ecosystem service
functioning
Lowered ecological and taxonomical
diversity
– altered community composition
Background
• Previously PAH30: 130,1300 and 13 000 µg/kg (dw) for 60 days
– Meiofauna - change in community composition
– Microbial community - less ability to transform ammonium to nitrate
C
L
M
H
D2
C L M H
D30
C L M H
D60
C L M H
Problem/Objective
Observed effects on nutrient turnover were transient or a result of more
permanent effects?
-tolerance?
“Deceived” that a community are non-affected, when exposed to oil.
Objective:
1. Can microbial communities develop tolerance to
PAHs?
2. Does tolerance leads to a less efficient community
with respect to nutrient turnover?
3. Tolerance developed in the field?
Tolerance
•
Tolerance
– organisms with a more tolerant genotype to the stress are selected for in a population
– more sensitive organisms succumb to the stress or gets eliminated through competition
– loss of genetic diversity
Effect
tolerance
Conc.
Experimental setup
• Treatments: increase in PAH levels 0.3 (Low) and 1.6 times (High) + C
• Short-term toxicity tests (PICT):
– Day 30, 60 and 90
– Re-exposure to PAHs
•
Molecular study - proportion of nitrifying bacterial communities, change over time
Pollution Induced Community Tolerance
(PICT)
• Communities exposed over time, to an anthropogenic substance
– Elucidate tolerance
– Shown before - heavy metals, antifouling agents, pesticides
• Detection
– Communities re-exposed in short-term toxicity tests
– Endpoint - photosynthesis, respiration or nitrification
– EC50 – EC10
• Control baseline tolerance vs exposed communities
– significant increase in the measured endpoint indicates
tolerance.
Short-term toxicity test
Control
nitrification (% of control)
120
D60
100
Endpoints - potential nitrification
- potential denitrification
80
Re-exposure :
0, 161, 580, 1610, 5800 and 16 100
(µg PAH/kg sediment (dw) [n=5])
60
40
20
0
0
1
2
3
4
log Conc.
5
6
7
Results
-tolerance
Objective 1
• Development of tolerance
-Day 60 and 90, significant difference
-H, slower development, initial exposure
5,0
*
*
*
EC10 log PAH (µg/kg)
4,0
3,0
2,0
1,0
0,0
C
L
D30
H
C
L
D60
H
C
L
D90
H
Results
Objective 2
• Developed tolerance resulted in reduced
nitrification efficiency
• 6-17 %
– reduced efficiency
Field study
• Site 5, 7-8 control sites
• Sediment samples to the lab
-PICT study.
Objective 3
• Site 1 significant higher average EC10
values compared to control sites
• tolerance to PAHs
• Site 1 significant lower ΣNOx
production rate, ~37 % compared to
the control sites.
EC10 logPAH (µg/kg)
15
*
10
5
0
1
2
3
4
5
Site
6
7
8
Average
controls
Conclusions
Ammonium oxidizing microorganisms can develop tolerance when exposed to
low concentrations of PAHs for >60-90 days.
Tolerance leads to a less efficient community with respect to nutrient turnover
- fitness cost
- 6-37 %
Implications
The possibility for development of tolerance needs to be taken into
account,
- to avoid being “deceived” that a community is non-affected
Potential nitrification can be used for evaluation of marine microbial
health.
Introduction of tolerance, in an area can lead to a lower turnover of
organic material, further contributing to eutrophication effects in
near-coastal areas.
Acknowledgements
Berne Petersson
Ursula Schwarz
Linda Hasselberg Frank
Pia Engström
Linda Svanberg
Contact:
[email protected]