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STUDY TITLE: Microbial biodegradation of Alaska North Slope crude oil and Corexit 9500 

in the Arctic marine environment

REPORT TITLE: Microbial biodegradation of Alaska North Slope crude oil and Corexit 9500 in the 

Arctic marine environment 

CONTRACT NUMBERS: Award number M17AC00005 

SPONSORING OCS REGION: Alaska

APPLICABLE PLANNING AREA(S): Beaufort Sea, Chukchi Sea

FEDERAL FISCAL YEAR(S) OF PROJECT FUNDING: FY17-20 

COSTS BY FISCAL YEAR: FY17: $97,491 FY18-19: $174,931

PROJECT MANAGER: Dr. Mary Beth Leigh 

AFFILIATION OF PROJECT MANAGER: Institute of Arctic Biology, University of Alaska

Fairbanks

ADDRESS: 2140 Koyukuk Drive, P.O. Box 757000, Fairbanks, AK 99775-7000

PRINCIPAL INVESTIGATORS: Mary Beth Leigh, Sarah Hardy 

KEYWORDS: Oil spill, biodegradation, Corexit 9500, dispersants, microorganisms, seawater, 

sediment, benthos, 

BACKGROUND: As rapid change occurs in the Arctic marine environment due to climbing 

atmospheric temperatures, current projections state that the summer Arctic will be nearly icefree by 2030. Previously ice-covered waters are becoming more accessible to human activities, 

increasing the likelihood of anthropogenic disturbance and contaminant exposure through oil 

and gas development and the expansion of commercial shipping and other activities. Microbial 

biodegradation is the primary means through which oil is naturally removed from the marine 

environment following a spill. Understanding oil biodegradation potential is important in 

predicting the fate and effects of oil in the environment. This information is also valuable for 

developing appropriate spill response strategies, including those that rely upon biodegradation. 

The use of chemical dispersants, such as Corexit 9500, is a common oil spill response strategy 

for oil slicks on open water. Dispersants have been widely applied in temperate and sub-tropical 

regions and were applied in large quantities during the Gulf of Mexico Deepwater Horizon oil 

spill. While Corexit 9500 is credited with protecting shorelines and facilitating biodegradation, it 

is also the subject of controversy regarding its effects on the fate of oil and its impacts on the 

environment. The interactions between oil and dispersants are not well understood in Arctic 

marine ecosystems, and the biochemical pathways and bacterial taxa involved in the 

biodegradation of the chemical components of dispersants are unknown. Another overlooked 

area of oil spill research, particularly in the Arctic, is the oil biodegradation potential of the 

indigenous microbial communities within the benthos, where a significant amount of oil may 

reside following a spill. In this project, we addressed a suite of questions related to the 

biodegradation of oil and Corexit 9500 in Arctic seawater, the biodegradation of oil in sediments, 

and the microorganisms and genes involved in these processes. This series of studies was 

conducted in the interest of providing basic scientific information that advances ecological 

knowledge and aids society in better responding to and predicting the fate of oil spills in the 

Arctic marine environment.

OBJECTIVES: 

1. Quantify the extent of oil and Corexit 9500 biodegradation over time and the effects 

of their co-presence in Arctic seawater on their fate. 

2. Identify microorganisms important to biodegradation of oil and dispersant chemical 

components in Arctic seawater and their overlaps and/or potential interactions. 
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3. Characterize the pathways and genes (and their taxonomic affiliations) involved in 

the biodegradation of petroleum hydrocarbons and Corexit 9500 in Arctic seawater. 

4. Assess the capacity for biodegradation of fresh and weathered Alaska North Slope 

crude oil by indigenous microorganisms in subtidal Arctic marine sediments under 

aerobic and anaerobic conditions. 

5. Identify microorganisms indigenous to Arctic marine sediments that are important to 

oil biodegradation. 

6. Utilize taxonomic information from sediment incubation studies to assess the 

distribution of putative hydrocarbon-degrading microbes more broadly in Arctic 

sediments 

7. Identify and compare microorganisms involved in biodegradation of oil in both Arctic 

seawater and sediments. 

DESCRIPTION: The goals of this project were to investigate the biodegradation of Alaska 

North Slope crude oil in Arctic seawater and sediments to better predict the fate of spilled oil 

in the Arctic marine environment and to assess the potential fate and effects of the chemical 

dispersant Corexit 9500 as an oil spill response strategy. For our Arctic seawater studies, we 

quantified the biodegradation of oil and Corexit 9500 components and applied in-depth 

analyses of microbial community structure and gene expression to gain a comprehensive 

perspective of microbial biodegradation and fate of petroleum and Corexit 9500 in the 

environment. We also conducted mesocosm incubation experiments using Arctic marine 

sediments with the addition of fresh and weathered crude oil under both oxic and anoxic 

conditions. We assessed aerobic and anaerobic biodegradation potential and identified oildegrading microbes present in the benthos under different treatments and at different 

periods. Following the identification of putative oil-degrading bacteria in incubation tests 

using Chukchi marine sediments, we queried existing microbial community datasets from 

sediments across the Beaufort Sea to assess the biodegradation potential present in 

indigenous sediment microbial communities across the region. 

SIGNIFICANT CONCLUSIONS: In this study, we found no evidence that Corexit suppressed 

crude oil biodegradation or oil-degrading microorganisms. Our experiments revealed that, 

when oil and Corexit were present in seawater together, the non-ionic surfactants (Span 80, 

Tween 80, Tween 85) were degraded rapidly, followed by subsequent biodegradation of oil 

components. This apparent preferential degradation of non-ionic dispersant components did 

not result in significant reductions in oil loss when Corexit was present. Analytical variability 

when quantifying the Corexit component DOSS precluded definitive determination of its 

degradation. Still, results indicated that it is more persistent than the non-ionic surfactants. 

DOSS appeared to undergo some biotransformation to EHSS while oil and other Corexit 

components were also being degraded. In Arctic seawater, some taxa responded only to the 

presence of oil (Thalassolituus, Sedimentalea) or Corexit (Colwellia, Polaribacter, Moritella, 

Octadecabacter, and Amylibacter) alone, implicating them as degraders of those mixtures. 

Some members of the taxa Oleispira, Pseudofulvibacter, and Roseobacter, became enriched 

in response to both oil and Corexit (when provided separately or together), suggesting that 

these organisms are capable of utilizing components of both mixtures. We propose a 

hypothetical Corexit component degradation pathway that utilizes the fatty acid β-oxidation 

pathway to break down side-chains of the non-ionic and DOSS surfactant components of 

Corexit 9500. Fatty acid oxidation is a common metabolic pathway in bacteria, so Corexit 

surfactant compounds may be readily metabolized, entirely or in part, by the many different 
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taxa that have responded to the presence of Corexit. In sediments, oil-associated shifts in 

microbial community structure were characterized by increases in the relative abundance of 

several taxa, which implicates these taxa as oil biodegraders. The taxa enriched in the 

presence of oil, Cycloclasticus, Neptuniibacter, Oleispira, Roseobacter clade NAC11-7, and 

Zhongshania, have all been previously linked to oil degradation. We assessed the 

distribution of these taxa across a geographically distributed series of Beaufort Sea sediment 

samples. The majority of putative oil-degrading taxa found in Chukchi marine sediments 

were also present in very low abundances in Beaufort Sea marine sediments, suggesting 

that putative oil-degraders are broadly distributed in North American Arctic sediments. The 

presence of oil stimulated different hydrocarbon-degrading organisms in seawater

(Thalassolituus, Sedimentalea, and Pseudofulvibacter), versus sediment (Cytoclasticus, 

Neptuniibacter, and Zhongshania), with some taxa being stimulated in both environments 

(Oleispira and Roseobacter). This highlights both the diversity and ubiquity of hydrocarbondegrading microbes. Our investigations of the biodegradation of oil, including individual 

components, in Arctic marine sediments, were still in progress and the close of this project. 

Oil loss data will be included in future publications that result from this study. Our findings 

provide an in-depth analysis of the crude oil biodegradation potential in the Arctic marine 

environment.

STUDY RESULTS: In Arctic seawater, biodegradation of crude oil and Corexit components 

were observed, with the non-ionic surfactants of Corexit being degraded prior to biotic 

petroleum hydrocarbon degradation. No suppression of crude oil biodegradation in the 

presence of Corexit was observed. However, prolonged increased concentrations of ethylhexyl 

sulfosuccinate (EHSS), a biotransformation product of the Corexit component dioctyl sodium 

sulfosuccinate (DOSS), indicated that mineralization of DOSS was delayed in the presence of 

oil. Oil and Corexit enriched different microbial communities in seawater; however, some taxa 

(Oleispira, Pseudofulvibacter, and Roseobacter) responded to both, suggesting they are 

capable of utilizing both oil and Corexit components. Some taxa responded only to the 

presence of oil (Thalassolituus, Sedimentalea) or Corexit (Colwellia, Polaribacter, Moritella, 

Octadecabacter, and Amylibacter) alone. Metatranscriptomics (gene expression) analyses of 

the seawater microbial communities revealed that, while oil and Corexit stimulate different 

overall metabolic gene expression profiles in the microbial community, they share upregulation 

of the pathway for fatty acid degradation, indicating a synergistic response when both oil and 

Corexit are present. This, along with the evidence of increased overall metabolic activity when 

oil and Corexit are both present (versus alone), supports the theory that dispersants stimulate 

the oil-degrading activity of the existing microbial community. The upregulation of fatty acid 

degradation gene expression in the presence of Corexit indicates that this pathway plays a role 

in the degradation of Corexit components. Thus, we propose a hypothetical degradation 

pathway that utilizes the fatty acid β-oxidation pathway to break down the non-ionic and DOSS 

surfactant components of Corexit 9500. In Arctic marine sediments, molecular analyses of the 

microbial community response to oil in aerobic incubations revealed that significant community 

shifts occurred in the oiled treatments, with distinct microbial community structures emerging 

following exposure to fresh versus weathered oil. Oiled communities also differed overall from 

those in non-oiled treatments. The oil-associated shifts were characterized by increases in the 

relative abundance of several taxa, implicating these taxa in oil biodegradation. The taxa 

present in oil treatments, but absent in non-oiled samples, were Cycloclasticus, Neptuniibacter, 

Oleispira, Roseobacter clade NAC11-7, and Zhongshania, which have all been previously 

linked to oil degradation. Our quantification of the biodegradation of oil in Arctic marine 

sediments is still in progress due to technical challenges, and oil loss data will be included in 

the final draft of this report. Following our identification of putative oil-degrading taxa in 

Chukchi Sea sediment incubation studies, we assessed the distribution of these taxa across a 
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series of Beaufort Sea sediments. We found that the majority of putative oil-degrading taxa 

found in Chukchi marine sediments were also present in very low abundances in Beaufort Sea 

marine sediments. The presence of these microbes indicated that oil degradation potential is 

broadly distributed in the Beaufort Sea benthos. A comparative analysis of putative oildegrading taxa identified in our seawater and sediment studies revealed that oil stimulated 

different hydrocarbon-degrading organisms in seawater (Thalassolituus, Sedimentalea, and 

Pseudofulvibacter), versus sediment (Cytoclasticus, Neptuniibacter, and Zhongshania), with 

some taxa being stimulated in both environments (Oleispira and Roseobacter). 

STUDY PRODUCTS 

Oral presentations 

2018 – CMI Annual Research Review, Anchorage, AK – Mary Beth Leigh 

2019 – CMI Annual Research Review, Anchorage, AK – Alexis Walker 

2020 – CMI Annual Research Review, Anchorage, AK – Mary Beth Leigh 

Gofstein, T. R. and Leigh, M. B. Fate and Influence of Petroleum Contamination and Chemical 

Dispersants in Arctic Marine Environments. 2017 Week of the Arctic, Fairbanks, AK, May 9-10, 

2017. 

Gofstein, T. R. & Leigh, M. B. Fate and Influence of Petroleum Contamination and Chemical 

Dispersants in Arctic Marine Environments. UAF Environmental Chemistry Symposium, 

Fairbanks, AK, April 21, 2017. 

Gofstein, T. R. and Leigh, M. B. Fate and Influence of Petroleum Contamination and Chemical 

Dispersants in Arctic Marine Environments. UAF Biomedical Research Conference, Fairbanks, 

AK, May 18, 2017. 

Leigh, Mary Beth, Kelly McFarlin, Taylor R. Gofstein, Ursel Schuette, Matthew Perkins, and 

Jennifer Field. Investigating Oil Spill Response Products Corexit 9500 and Oil Spill Eater II: 

Composition, Fate, and Effects on Oil Biodegradation in Alaskan Waters. Invited presentation. 

Alaska Oil Spill Technology Symposium. Anchorage, AK, March 28-29, 2018. 

Gofstein, T.R. Fate and Effects of Petroleum Contamination and Chemical Dispersants in Arctic 

Marine Environments.UAF Annual Environmental Chemistry Symposium, Fairbanks, AK, April 7, 

2018. Received Outstanding Graduate Presentation award. 

Leigh, M.B., et al. Investigating Oil Spill Response Products Corexit 9500 and Oil Spill Eater II: 

Composition, Fate, and Effects on Oil Biodegradation in Alaskan Waters. Alaska Branch of the 

American Society for Microbiology Annual Meeting. Fairbanks, AK. September 29, 2018. 

Leigh M.B, et al. Fate and Effects of Oil and Oil Spill Response Chemicals in Alaskan Marine 

Environments. UAF Institute of Arctic Biology Life Sciences Seminar Series, November 9, 2018. 

Leigh M.B, et al. Fate and Effects of Oil and Oil Spill Response Chemicals in Alaskan Marine 

Environments. UAF Institute of Marine Sciences Seminar Series, November 14, 2018. 

Gofstein, T.R. & Leigh, M. B. Biodegradation of Crude Oil and Corexit EC9500A in Arctic 

Seawater. Fifth International Symposium on Bioremediation and Sustainable Environmental 

Technologies, Baltimore, Maryland, April 18, 2019. 

Leigh M.B, et al. Fate and Effects of Oil and Oil Spill Response Chemicals in Alaskan Marine 

Environments. University of Oklahoma Department of Microbiology and Plant Biology. 

November 6, 2019. 
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Poster presentations 

Gofstein, Taylor R., Matthew Perkins, Jennifer Field, and Mary Beth Leigh. Biodegradation of 

Crude Oil and Corexit EC9500A in Arctic Seawater. Alaska Oil Spill Technology Symposium. 

Anchorage, AK, March 28-29, 2018. 

Gofstein, Taylor R., Matthew Perkins, Jennifer Field, and Mary Beth Leigh. Biodegradation of 

Crude Oil and Corexit EC9500A in Arctic Seawater. Alaska Branch of the American Society for 

Microbiology Annual Meeting. Anchorage, AK, Oct 18-19, 2019. 

Manuscripts in preparation 

Gofstein, T., Perkins, M., Field, J. and Leigh, M. B. Sequential degradation of crude oil and 

Corexit EC9500A in Arctic seawater. Manuscript submitted to Applied and Environmental 

Microbiology (May 2020). 

Gofstein, T. R. & Leigh, M. B. Microbial metatranscriptome shifts suggest shared biodegradation 

pathways for Corexit 9500 components and crude oil in Arctic seawater. Manuscript in 

preparation. 

Walker, A., S. Hardy, and M.B. Leigh. Biodegradation of Alaska North Slope crude oil in Arctic 

marine sediments. Manuscript in preparation. 

Maps of study areas 

Map 1. Map of the study area and collection location for sediment incubation experiment. 

The Arctic marine sediment sample collection site was approximately 130km offshore of Pt. Lay 

Alaska. 
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Map 2. Distribution of putative oil-degraders found in Beaufort Sea marine sediments. 

This map shows locations where bacterial genera common to both Chukchi and Beaufort 

sediments were identified.