microbial respiration of oil in surface
TRANSCRIPT
Microbial respiration of oil in surface waters in close proximity to the
Deepwater Horizon site.Deepwater Horizon site.Benjamin Van Mooy, Bethanie Edwards, Christopher Reddy, Richard Camilli Catherine Carmichael Krista LongneckerRichard Camilli, Catherine Carmichael, Krista Longnecker
Woods Hole Oceanographic Institution
h d b dResearch supported by NSF‐OCE RAPID Awards
See: Edwards et al., (2011) Environ. Res. Lett.
Station locations in close proximity to Deepwater Horizon site.
28.8
29.0 Outside of slick Inside of slick DWH site Pomeroy et al., 1995
Latit
ude
(o N)
28.4
28.6On site June 19 to 28, 2010 aboard R/V Endeavor.
L
28.0
28.210 nmVan Mooy, 2003
100 nm
Longitude (oW)
87.087.588.088.589.089.5
Previous evidence of phosphorus limitation of microbial respiration
d-1)
15Right: Results obtained in area of DWH in June of 1993 by Pomeroy et al.
atio
n (
M O
2 10
(1995) Mar Ecol Prog Ser
In July of 2002, SRP concentrations of 12 nM
Res
pira
5
concentrations of 12 nM and turnover time of 1.0 ±0.2 hour s (Van Mooy, 2003, unpublished data)
Control Glucose Nitrogen Metals Phosphorus0
H h i I Mi b bl d il i f li k
Hypotheses and approaches
Hypothesis I: Microbes unable to respond to oil in surface slick
Approach: Compare microbial rates and abundances inside and outside of the surface slick.‐Enzyme assays – standard methods using fluorogenic substrates.y y g g‐ Respiration – track O2 in BOD bottles equipped with oxygen optodes‐ Hydrocarbon degradation – track hydrocarbons in bottle incubations by GC/FID‐Microbial biomass – intact polar lipid concentrations by HPLC/MSMicrobial abundance SYBR Green staining and flow cytometry‐Microbial abundance – SYBR Green staining and flow cytometry
Hypothesis II: Microbes limited by inorganic nutrients
Approach: Compare incubations amended with nutrients versus non‐amended controls.‐ Amendment: 32 µM NH4NO3, + 2 µM KH2PO4 in HPLC grade water‐ Control : HPLC grade water
Statistics: Single analyses from triplicate samples. Error bars are magnitude of range. Differences delineated by non‐parametric tests.
For complete methods see Edwards et al., (2011) Environ. Res. Lett.
Enhanced phosphorus stress inside slick
Alkaline phosphatase activities were higher inside the slick than outside the slickslick.
Soluble reactive phosphorus (i.e. phosphate) ranged from 5 to 16 nM, but there were no differences between inside and outside of the slick.and outside of the slick.
Enhanced respiration inside slick, but nutrient limited?
In 36‐hour incubations, respiration rates inside the slick were about 5 times faster on average than outside the slickoutside the slick.
Enhanced by an average of 9.9 µM O2 d‐1.
Nutrient amendments led to a range of responses, from as much as a doubling in theas much as a doubling in the microbial respiration rate to no effect.
Respiration rates were consistent over time.
(M
)
220
240
260
conc
entra
tion
160
180
200
Replicate 1
Longer‐term incubation (6 days) showed that respiration was relatively constant for
l d
Oxy
gen
c
100
120
140 Replicate 2Replicate 3Linear regression (R2 = 0.9872)95% Confidence Band 95% Prediction Band
several days.
Time (days)
0 2 4 6 880
Can we estimate the total impact of microbial respiration?
Experimental Marine Pollution Surveillance Reports: slick 5,600 to 24,000 km2 during our , , gcruise.
Extrapolating enhanced respiration over slick area inrespiration over slick area in surface mixed layer of 15 m yielded an estimated potential microbial respiration rate of 6 x 108 to 3 x 109 moles C d‐1
On the same order as oil leaking from well whichleaking from well, which averaged 6 x 108 moles C d‐1.
Respiration in slick was fueled by hydrocarbon degradation
Hydrocarbon degradation equivalent to 7.1 µM O2 d‐1, q µ 2 ,which is 71% of observed enhanced respiration rate of 9.9 µM O2 d‐1.
2.2
2.4
Hydrocarbon concentration (mg/l)n-C18/phytane ratio
First‐order rate law yields hydrocarbon degradation rate of about 4 to 6% per day.
1.8
2.0
Decrease in ratio of nC18/phytane is consistent with microbial degradation 1 2
1.4
1.6
with microbial degradation.
Time (d)
0 1 2 3 4 5 6 71.2
How to our observed hydrocarbon degradation rates compare?
Experimental Marine Pollution Surveillance Reports show a rapid er
s) 10000Reports show a rapid decrease in the area of the slick.
e ki
lom
ete
6000
8000
After July 15th, the first‐order disappearance rate was about 8 to 12 % per day (R2=0 7020) ck
(squ
are
4000
6000
(R =0.7020)
Compare to hydrocarbon degradation rate from A
rea
of s
li
0
2000
bottles of 4 to 6% per day.
Time (July calendar date)0 5 10 15 20 25 30
A 0
Enhanced respiration in slick, but no increase in microbial biomass
Phosphatidylglycerol (PG) and phosphatidylethanolamine (PE) are common membrane phospholipids in marine heterotrophic bacteria.
Sulfoquinovosyldiacylglycerol(SQDG) abundant in picocyanobacteria.
Cell abundances by flow cytometry show fewer microbies in slick (not shown);microbies in slick (not shown); sampling artifact?
Van Mooy et al., (2006), PNAS; Van Mooy et al., (2009) Nature; Van Mooy and Fredricks (2010) Geochim. Cosmochim. Acta; Popendorf et al. (2011) Org. Geochem.
Microbial growth limited by nutrients.
Microbial abundances and biomass increase inbiomass increase in response to nutrient amendments, in some cases by as much as a factor of two.
H h i I Mi b bl d il i f li k→ d
Conclusions
Hypothesis I: Microbes unable to respond to oil in surface slick → not supported.
Oil in slicks led to anomalously high rates of microbial respiration.
Respiration rates of 9.9 µM O2 d‐1 extrapolated across the slick indicated that microbes may have had the potential to remove all of the oil from the surface slicks. This potential was could NOT have been realized.
Hydrocarbon degradation proceeded at a rate of about 4 to 6% per day, which based on our crude analysis of satellite data products suggests microbial degradation was responsible for between 30 to 80% of slick disappearance.
Hypothesis II: Microbes limited by inorganic nutrients → some support.
Microbial biomass was similar inside and outside of the slick suggesting thatMicrobial biomass was similar inside and outside of the slick suggesting that growth was limited by nutrients.
Nutrient amendments stimulated both respiration and growth.
Thank you.y