A lot has been said, written, and discussed about the recent Oil Spill in the Gulf of Mexico. The spill has been capped but the damage remains. The Gulf of Mexico has now become the feedstock of several battles, fierce and feeble, in the legal, political and scientific realm. What battles you say? It’s what on your mind as well – What will happen of the Gulf of Mexico? What do we need to do to save the physical, chemical and biological environment? And the worst of all – Is the damage irreversible?
Sadly, we don’t have any answers yet. And let’s face it – there is no right answer. What we do have are cues from the environment itself. Scientists from the Lawrence Berkeley National Laboratory, University of Oklahoma, Pacific University, and The Lawrence Livermore National Laboratory have taken the proverbial stethoscope and are listening intently to the heartbeat of the deep underwater plume near the wellhead…and they have good news for us. In a recent paper, published in the journal Science, these scientists report some of their latest findings on the microscopic life that is abuzz in the hydrocarbon plume near the wellhead where the oil spill occurred.
Why is an oil spill an environmental hazard in the first place? Crude oil, as you may know, is a cocktail of high molecular weight aromatic hydrocarbons such as isopropyl benzene, n-propylbenzene, and naphthalene. These hydrocarbons are extremely persistent in the environment, which means that most organisms cannot use them as a substrate for growth or energy, nor do they get degraded by physical or chemical processes. Add to that, the fact that some of these chemicals are highly toxic and a few of them carcinogenic. So when oil spills occur, especially in such large quantities in such a small amount of time, it leads to a sudden loss of flora and fauna and a major imbalance in the prevalent ecosystem. These large opaque clumps of crude oil emanating from the Earth’s interior can be reduced to tiny droplets that can disperse in the water column by adding chemicals known as dispersants. If the sudden insurgence of crude oil in the marine ecosystem wasn’t hard to deal with, the organisms in the deep sea near the hydrocarbon plume in the Gulf had to also deal with the added toxicity of Corexit 9500 – the dispersant that was added in copious quantities soon after the spill.
Did anyone survive this massive onslaught? Surprisingly, yes! The authors of this study took samples from the deep sea up to 10 kms( 6.2 miles) away from the wellhead and saw that around the depth where the oil spill occurred there was a slight reduction in the amount of oxygen. This reduction in oxygen levels, usually indicative of respiration by living beings, was the first clue that led them to think that life is prospering in these toxic waters. They knew, from previous studies, that these living beings had to be microorganisms especially bacteria. With an a priori hypothesis that bacteria are living in this hydrocarbon plume, the authors went on to measure the density of bacteria in the water column in the Gulf and their hypothesis was proved right — the cell density was especially high just at the depth where the oil spill occurred. With these exciting preliminary results, the authors decided to take water samples near the plume and peer at them under the microscope and there was living proof – their paper has a few pictures of big, fat bacteria happily chomping down the hydrocarbons.
Where did these bacteria come from? How can they survive? Further analysis showed that there is a wide diversity of bacteria in the deep sea waters of the Gulf. Samples that the authors extracted from parts of the deep sea that were not affected by the oil spill showed up to 951 different bacterial taxa. Only 16 of them were found in the hydrocarbon plume. Did these 16 taxa just get lucky? No way, luck rarely works in the natural environment. These 16 taxa of bacteria, not surprisingly, have representatives, that have previously been reported to eat up hydrocarbons especially at low temperatures (as observed in the deep sea). How did these 16 taxa get to the plume? They didn’t happen to get there by luck either, they were already present in the deep sea water before the oil spill but were not as abundant because they were competing with many other taxa for food and resources. When there was a sudden insurgence of oil into their ecosystem, whilst most other bacteria perished, they survived because they could eat up the oil. Their numbers increased rapidly. Selecting for certain taxa that can degrade persistent compounds in the natural environment is termed by environmental engineers as ‘enrichment’. The authors analyzed the phospholipid fatty acids – components of the bacterial cell membrane, used as a signature for identifying different taxa – of bacteria in the plume to further deduce that there were two distinct groups of a taxa known as Oceanospiralles. Oceanospiralles have been found in hydrocarbon-enriched environments commonly and some of them are also known to be psychrophiles (cold-loving). Oceanospiralles are capable of surviving an oil spill because they contain genes for hydrocarbon utilization, such as the phdCI gene that is needed for naphthalene degradation.
These results show that the microbial community in the deep sea hydrocarbon plume in the Gulf of Mexico has already undergone a rapid adaptive shift. Selection has led to the formation of a new-fangled community that is not as diverse but highly specialized to degrade the oil. Apart from marveling at the rapid, dynamic response of the microscopic super heroes we must realize that these results imply that there is an intrinsic potential for bioremediation (removal of contaminants by microbes plants etc.) of oil contamination in the Gulf. We must devise our clean-up plans keeping them in mind.
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