A review of: Bethanie R Edwards et al (2011). Rapid microbial respiration of oil from the Deepwater Horizon spill in offshore surface waters of the Gulf of Mexico. Environ. Res. Lett. 6 (July-September 2011) 035301.
The Deepwater Horizon disaster is known to be the largest offshore oil spill in history. It happened in April 2010 when the drilling platform suffered a methane explosion and fire, resulting in the platform sinking. Over 600 million litres of oil seeped out into the sea before the well could be finally plugged. The fate of the oil is still not fully understood and this study explores the key role that microbes play in the degradation of the surface water oil.
Microbes can aid in the degradation and remediation of oil as they respond quickly to the addition of petroleum hydrocarbons. However, in doing this they are limited by the availability of phosphate, and in the case of this study, the offshore waters near the site of the spill are oligotrophic. This lack of inorganic nutrients would lead to microbes giving a more minimal response to the oil and at a slower rate.
In order to prove that this is the case for microbes, the researchers collected surface-water samples at twelve locations around the site of the spill. They used the same sites as previous studies researching the effects of the oil spill so as to correlate results. Measurements were taken for community respiration rates, lipase enzyme activities, microbial abundances, microbial and microbial biomass. To investigate the limitations that phosphate provides measurements of phosphate concentrations and activities were also taken. Hydrocarbon degradation rates were also measured and correlated with community respiration rates in order to further ascertain the fate of the oil.
The results of the study revealed that phosphate was scarce at all twelve sites and there was also no difference between areas inside and outside of the oil slick. Alkaline phosphatases (enzymes used by the microbes in order to access DOP when phosphate is scarce) were however significantly higher within the slick, indicating enhanced phosphorus stress. This shows that microbes within the slick were under higher stress due to the higher demand for phosphorus caused by the availability of organic carbon in the oil.
Community respiration rates were found to be five times greater within the oil slick compared to outside of it, indicating enhanced oxidation of organic carbon. Microbes clearly were able to readily respond to the addition of hydrocarbons despite the phosphorus stress, which is against what was predicted.
Lipase activity was also enhanced inside the slick. It is thought that this must be due to the addition of DOSS (Dioctyl sodium sulfosuccinate) which was in the dispersants used in response to the oil spill. This chemical contains many for ester linkages than in crude oil and so is thought to have encourages the activity. It is also possible that the enhanced respiration in microbes was due to the oxidation of dispersants in addition to hydrocarbon degradation.
Bacterial and phytoplankton biomass were suggested to be relatively constant throughout the study, whether within slicks or not. Microbial growth was stunted within the slick, despite increased lipase activity, phosphatase activity and enhanced respiration. It is thought from looking at previous studies that top-down processes such as grazing are the cause of this. An increase in respiration in response to nutrient changes is consistent with past studies and concludes that the addition of nitrogen and phosphorus to oil contaminated seawater results in faster degradation of hydrocarbons.
The study very much highlights the underestimated abilities of microbes. The observations have shown just how rapid the response of microbes can be, even in the face of huge stress and limitation. It also explains the unknown interactions between the microbes and the human defence of using dispersants which helped to break down the oil to a state which the microbes could possibly more easily degrade it.
The Deepwater Horizon disaster is known to be the largest offshore oil spill in history. It happened in April 2010 when the drilling platform suffered a methane explosion and fire, resulting in the platform sinking. Over 600 million litres of oil seeped out into the sea before the well could be finally plugged. The fate of the oil is still not fully understood and this study explores the key role that microbes play in the degradation of the surface water oil.
Microbes can aid in the degradation and remediation of oil as they respond quickly to the addition of petroleum hydrocarbons. However, in doing this they are limited by the availability of phosphate, and in the case of this study, the offshore waters near the site of the spill are oligotrophic. This lack of inorganic nutrients would lead to microbes giving a more minimal response to the oil and at a slower rate.
In order to prove that this is the case for microbes, the researchers collected surface-water samples at twelve locations around the site of the spill. They used the same sites as previous studies researching the effects of the oil spill so as to correlate results. Measurements were taken for community respiration rates, lipase enzyme activities, microbial abundances, microbial and microbial biomass. To investigate the limitations that phosphate provides measurements of phosphate concentrations and activities were also taken. Hydrocarbon degradation rates were also measured and correlated with community respiration rates in order to further ascertain the fate of the oil.
The results of the study revealed that phosphate was scarce at all twelve sites and there was also no difference between areas inside and outside of the oil slick. Alkaline phosphatases (enzymes used by the microbes in order to access DOP when phosphate is scarce) were however significantly higher within the slick, indicating enhanced phosphorus stress. This shows that microbes within the slick were under higher stress due to the higher demand for phosphorus caused by the availability of organic carbon in the oil.
Community respiration rates were found to be five times greater within the oil slick compared to outside of it, indicating enhanced oxidation of organic carbon. Microbes clearly were able to readily respond to the addition of hydrocarbons despite the phosphorus stress, which is against what was predicted.
Lipase activity was also enhanced inside the slick. It is thought that this must be due to the addition of DOSS (Dioctyl sodium sulfosuccinate) which was in the dispersants used in response to the oil spill. This chemical contains many for ester linkages than in crude oil and so is thought to have encourages the activity. It is also possible that the enhanced respiration in microbes was due to the oxidation of dispersants in addition to hydrocarbon degradation.
Bacterial and phytoplankton biomass were suggested to be relatively constant throughout the study, whether within slicks or not. Microbial growth was stunted within the slick, despite increased lipase activity, phosphatase activity and enhanced respiration. It is thought from looking at previous studies that top-down processes such as grazing are the cause of this. An increase in respiration in response to nutrient changes is consistent with past studies and concludes that the addition of nitrogen and phosphorus to oil contaminated seawater results in faster degradation of hydrocarbons.
The study very much highlights the underestimated abilities of microbes. The observations have shown just how rapid the response of microbes can be, even in the face of huge stress and limitation. It also explains the unknown interactions between the microbes and the human defence of using dispersants which helped to break down the oil to a state which the microbes could possibly more easily degrade it.
2 comments:
Hey Sami!
I hope you've had a great break. Interesting review. One of Graham Bradley's final year project interests was on the subject you just covered. It would have been a good project to do but it entailed going around Cornwall all summer taking samples and Graham being busy as he is, it would have been an uphill struggle.
Did the authors mention what type of bacteria was being used to 'consume' the oil? I would imagine they would be something like or closely related to methanotrophs because petroleum is composed of hydrocarbons.
Hey Mario! :)
Christmas break has been great thanks, could do with being longer though! I hope yours was good too.
That sounds like it could be a very interesting project. But yes, Graham is certainly a very busy bee!
The paper i reviewed sets out to explore the role of microbes in the degradation of oil. But it doesn't go into depth about the type of bacteria, but moreso the effect the bacteria had.
However, methane was the most abundant hydrocarbon released during the spill, so methanotrophs certainly played a part in the clean up!
From reading around, it seems that 16 types of bacteria were found around the plume. All of which can break down hydrocarbons in oil. Big blooms of the bacteria arise in response to the oil. Oceanospirillales was found to be the most prominent Order of bacteria. Researchers are trying to take advantage of these oil-eaters by genetic manipulation so they can be exploited in future spills too.
Post a Comment