Oil-Degrading Microbes

Horel A, Mortazavi B, Sobecky PA. 2012. Seasonal Monitoring of Hydrocarbon Degraders in Alabama Marine Ecosystems Following the Deepwater Horizon Oil Spill. Water Air and Soil Pollution 223(6):3145-3154. Find it Online*
The salt marshes in Alabama have been impacted by the BP oil spill, but since these are delicate ecosystems, the best way to rectify the problem would be bioremediation (i.e., the use of microbes to degrade or remove a pollutant) by the local microbial community.  Various forms of bacteria have the ability to degrade oil, but the efficiency in bioremediation depends on physical and chemical parameters (e.g., pH, temperature, nutrients, sediment properties, and oxygen) that may vary seasonally.  Oil and alkane degraders (aerobic) were present consistently, but not polycyclic aromatic hydrocarbon (PAH; i.e., carcinogenic portion of oil) degraders.  There was a greater number of oil-degrading bacteria near the Spartina alterniflora (i.e., smooth cordgrass) at high tide level, due to the higher amount of organic material in the area. 

Hamdan L, Fulmer P. 2011. Effects of COREXIT EC9500A on bacteria from a beach oiled by the Deepwater Horizon spill. Aquatic Microbial Ecology 63(2):101-109. Find it Online*
Oil-degrading bacteria are essential in marine environments that are subject to frequent natural and anthropogenic seepage.  Some of the main oil-degrading bacteria in the Gulf of Mexico, were the Marinobacter sp., Acinetobacter sp., and Vibrio sp.  COREXIT, the chemical dispersant applied in the BP oil spill, was tested against these bacteria for toxicity purposes.  COREXIT contributed to a significant reduction in live:dead bacterial cells, with the exception of the Vibrio sp.  Proper dilution of ‘practically non-toxic’ COREXIT is 1:50, but this ratio was highly toxic to microbial communities directly involved in natural oil bioremediation.  COREXIT may impart positive effects on oil-degrading cultures capable of withstanding its initial toxicity because it can also be subject to mineralization (i.e., a result of bacterial degradation).  

Shiller AM, Joung DJ. 2012. Nutrient depletion as a proxy for microbial growth in Deepwater Horizon subsurface oil/gas plumes. Environmental Research Letters 7(4):045301. Find it Online*
Many times, microbial growth is used as a proxy for bioremediation or degradation success.  Microbial growth has been measured by oxygen depletion and/or microbial biomass, but nutrient (e.g. phosphorus and nitrogen) depletion was used in this study for a more accurate estimate of microbial growth/degradation.   Nutrient anomalies had a positive correlation with oxygen anomalies; this suggests that nutrients and oxygen were both removed by bacteria for degradation purposes.  Neither phosphate, nitrate, nor oxygen were limiting as an energy source.  The estimated bacterial carbon production in the submerged oil/gas plume is about 1/10 the annual primary production associated with the outflow of the Mississippi River.  

Urakawa H, Garcia JC, Barreto PD, Molina GA, Barreto JC. 2012. A sensitive crude oil bioassay indicates that oil spills potentially induce a change of major nitrifying prokaryotes from the Archaea to the Bacteria. Environmental Pollution 164:42-45. Find it Online*
Many times bacteria are suggested as the main source of bioremediation, especially after a big oil spill, but not all bacteria have the same biogeochemical function.  Oil spills may be deleterious to chemolithotrophic/chemoautotrophic bacteria (i.e., bacteria that do not need light or organic compounds for energy; bacteria that use reduced inorganic compounds and carbon dioxide).  Acute bioassays revealed that these bacteria are extremely sensitive (i.e., inhibition) to crude oil exposure.   Sensitivity to toxicity may be determined by the different surface:volume ratios regulated by cell size.  Oil contamination in marine environments can cause a shift in local microbial communities, so chemoautotroph abundance could be an excellent biomarker for detecting oil.

Tao Z, Bullard S, Arias C. 2011. High Numbers of Vibrio vulnificus in Tar Balls Collected from Oiled Areas of the North-Central Gulf of Mexico Following the 2010 BP Deepwater Horizon Oil Spill. Ecohealth 8(4):507-11. Find it Online*
A human pathogen and oil-degrading bacteria, Vibrio vulnificus, has been found in the tar balls washing ashore Mississippi and Alabama beaches.  This pathogen can cause deadly food poisoning and severe wound infections, by way of consuming contaminated seafood or contact through open cuts or sores.  Bacterial counts revealed that V. vulnificus was significantly higher in tar balls than in sand and seawater collected at the same location.  Researcher’s data suggest that tar balls can act as reservoirs for bacteria including human pathogens.  

Chakraborty R, Borglin SE, Dubinsky EA, Andersen GL, Hazen TC. 2012. Microbial Response to the MC-252 Oil and Corexit 9500 in the Gulf of Mexico. Frontiers in Microbiotechnology, Ecotoxicology and Bioremediation 3:357. Find it Online*
The deepwater oil plume was greater than 35 km in distance and 30% was still in the water column.  In May 2010, the bacterial count for the deepwater plume was 55,000 cells/ml and only 27,000 cells/ml outside of the plume.  There was a microbial shift in the deepwater community as the chemistry and nature of the oil changed.  Specific phases of oil degradation, oil abundance, nutrients, and temperature can determine the microbial diversity.  The dispersant, Corexit 9500, may have been an extra carbon source for bacteria.  Different bacterial species were able to degrade various components of the Corexit (e.g., DOSS, glycols, hydrocarbons). 

Redmond MC, Valentine DL. 2012. Natural gas and temperature structured a microbial community response to the Deepwater Horizon oil spill. Proceedings of the National Academy of Sciences of the United States of America 109(50):20292-7. Find it Online*
The BP oil spill was infamous for the oil contamination in the cold, deep portions of the Gulf of Mexico, but little attention is focused on the discharged natural gas.  Methane-degrading bacteria are usually limited in terms of degrading oil and oil-degraders are usually limited in terms of degrading gases.  Temperature has a direct effect on microbial physiology and an effect on the physical properties of oil that influence its bioavailability.  Crude oil is a mixture of hydrocarbon compounds that differ in volatility and solubility and are degraded at different rates.  The composition of the benthic microbial community has been identified and different bacteria degrade this material based on compound properties, phase (e.g., gas or liquid), and temperature. 

Edwards BR, Reddy CM, Camilli RC, C. A., Longnecker K, Van Mooy BAS. 2011. Rapid microbial respiration of oil from the Deepwater Horizon spill in offshore surface waters of the Gulf of Mexico. Environmental Research Letters 6(3):035301.Find it Online*
Microbial (i.e., bacteria) respiration rates can be used as an indicator for biodegradation of organic material (e.g., oil or dispersants).  Microbial respiration rates increased heavily within the oil slicks upon surface waters in the Gulf of Mexico near the Deepwater Horizon incident.  The respiration rates were nearly 5x higher than outside the oil slick.  This was somewhat unsuspecting, since microbes usually need nutrients to be active and many parts of the Gulf of Mexico are oligotrophic (i.e., low nutrient content).  Even though respiration rates increased, there was no microbial growth or elevated biomass.  This may have been due to lack of nutrients or grazing control (i.e., predators).  Nonetheless, this study suggests that the microbes degraded oil at a rate that was of the same order as the delivery of the oil.  

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