Bacteria to the rescue?
The Deepwater Horizon disaster in the Gulf of Mexico last summer was front page news for weeks. The potential environmental damage has been estimated to be many billions of dollars to date, and will likely continue for years to decades to come. The accident was initially caused by an explosive release of methane by the drilling apparatus, which in turn led to the destruction by fire of the drilling platform and uncontrolled release of petroleum and methane into the Gulf. Estimates at the time of the spill suggested that 40% of the output of the well was in the form of methane. Unlike petroleum, the released methane is soluble in water, and monitoring of the levels of methane in seawater at the spill site was used to estimate the rate of release from the spill site.
Release of methane was worrisome in its own right. Methane is a greenhouse gas, and contributes to rises in global temperatures. One less likely scenario is the possibility of a methane-induced tsunami: a sudden release of a massive methane gas bubble could cause damaging wave action against the Gulf coastlines without any warning. Consequently, scientists had significant reason for monitoring levels of methane since the accident last spring.
Which brings us to an article from the scientific journal, Science. Monitoring of ocean methane levels throughout the spill are has indicated that levels throughout the spill area have returned to baseline, or pre-spill levels. Where did the methane go? As we’ll learn in Chapter 6, microorganisms can be incredibly variable in the kinds of carbon-containing compounds that they can use as an energy and a carbon source. Classes of bacteria called methanotrophs can use methane in the process of respiration, obtaining energy and carbon for cellular processes through the metabolism of methane.
In the Science article, the authors have estimated that the bacteria consumed 3.0 × 1010 moles of methane. At 16 grams per mole, that works out to approximately 500 million kilograms of methane. Just to put that in perspective, a typical propane tank for a barbecue grill contains approximately 25 pounds or 10 kilograms of propane. So we are talking about roughly 50 million tanks of this compound that have been eliminated from the environment.
This initially sounds as if it is a fantastic situation for fixing an environmental disaster, but there’s a potential terrible drawback as well. If the methantrophs are utilizing methane under aerobic (oxygen requiring) conditions, they will very rapidly deplete oxygen levels as they use methane. This can lead to the development of anoxic (oxygen depleted) conditions in the marine environment, which can in turn be catastrophic for organisms that depend on oxygen. Scientists have recently noted the development of “dead zones,” particularly during the summer, which have been attributed to the accumulation of agricultural runoff from the Mississippi River drainage basin, which leads to the depletion of oxygen (and marine animals) due to the action of bacteria. So, although microorganisms have potentially accelerated the degradation of compounds in this environmental disaster, the consequences to the ecosystem may continue or be exacerbated.