Normally, the absence of oxygen means an absence of life. But in the wake of the Deepwater Horizon Gulf oil spill, scientists noticed something curious happening in the water. Huge populations of methane-eating bacteria appeared out of nowhere, despite the fact that there had hardly been any of these bacteria present prior to the spill, and millions of gallons of toxic oil usually kill things, not bring them to life.
A few years later, scientists at the Massachusetts Institute of Technology (MIT) think they may have found an explanation for this phenomenon. Researchers have discovered a gene that enables bacteria to survive in extreme, oxygen-depleted environments, lying dormant until food — such as methane from an oil spill, and the oxygen needed to metabolize it — becomes available. The scientists are now taking a closer look at gene codes for a protein named HpnR that is responsible for producing bacterial lipids known as 3-methylhopanoids. It’s this gene scientists say could trigger nutrient-starved microbes to make a sudden appearance when the eating gets good.
“The thing that interests us is that this could be a window into the geologic past,” says MIT Department of Earth, Atmospheric and Planetary Sciences (EAPS) postdoc Paula Welander, who led the research. “In the geologic record, many millions of years ago, we see a number of mass extinction events where there is also evidence of oxygen depletion in the ocean. It’s at these key events, and immediately afterward, where we also see increases in all these biomarkers as well as indicators of climate disturbance. It seems to be part of a syndrome of warming, ocean deoxygenation and biotic extinction. The ultimate causes are unknown.”
Understanding more about how this particular bacterial lipid survives when there’s no food around, and then multiplies quickly when food is available could be key in developing biological tools to aid in oil spill cleanup.
To test the theory that it was the gene giving bacteria this uncanny survival skill, scientists created a mutant strain of bacteria with the gene deleted. In comparison tests with wild bacteria, this mutant strain struggled to maintain normal growth rates. With the gene added back in, growth resumed at a normal pace.
The results, Welander says, are especially exciting from a geological perspective. If 3-methylhopanoids do indeed allow bacteria to survive in times of low oxygen, then a spike of the related lipid in the rock record could indicate a dramatic decrease in oxygen in Earth’s history, enabling geologists to better understand periods of mass extinctions or large ocean die-offs.
Main image credit: Paula Welander/MIT