A Caribbean lake of liquid asphalt that makes a comfortable home for a unique mix of microorganisms may provide clues to how life could survive in hydrocarbon lakes on Saturn’s moon Titan.
Titan is the only body in the solar system other than Earth that sports liquid lakes, clouds and rain, a feature that has drawn interest from scientists hunting for alien life. But instead of water, Saturn’s largest moon is awash in liquid methane and ethane — molecules similar to the tar that paves terrestrial streets.
Some scientists think studying Pitch Lake on the island of Trinidad, a lake fueled by oil upwelling from underground, may be the next best thing to dipping a beaker in Titan’s lakes.
“This is the closest we can come on Earth to seeing what the moon of Saturn looks like,” says microbiologist Steven Hallam of the University of British Columbia in Vancouver.
Hallam and his colleagues analyzed samples from several different parts of Pitch Lake to see if anything lived there. They found a thriving community of microorganisms feeding on the hydrocarbons and pumping out methane and metals. The researchers’ results were posted online April 12 at arXiv.org and have been submitted to the journal Astrobiology.
Analyzing the samples was no easy task: the molasses-like goop got all over the lab, Hallam says, and because oil and water don’t mix, water couldn’t wash it off.
“It’s somewhat nasty,” says astrobiologist Dirk Schulze-Makuch of Washington State University in Pullman, who led the field study. If the thick gunk gets on your clothes, he says, you might as well just toss them out.
The study also created challenges in the lab. Because of tar and water’s unfriendliness, standard methods for isolating DNA didn’t work. “There are lots of commercial kits out there to get DNA from seawater, or from soil, or from blood,” Hallam says. “There’s no tar kit, though.”
Instead, Hallam and his colleagues froze bits of tar with liquid nitrogen and ground them to a powder to force the material to dissolve in a solution. The solution contained a chemical that broke open the microbes’ cells, letting their DNA spill out. Once the DNA was free and the tar was washed away, the researchers could purify the DNA using standard techniques.
The team found 20 different lineages of bacteria and nine lines of archaea, single-celled organisms that lack nuclei. Among them were anaerobic archaea that consume methane; others called Thermoplasmatales, which derive energy from metals; and entirely new types of archaea that had never been seen before.
Not only was life in the lake different from life elsewhere on the planet, life in one corner of the lake was different from life in another.
“Every single sample that we looked at, the bacterial community was different,” Hallam says. The researchers think the microbes form a collaborative network, where one community of microbes eats what another community excretes.
Schulze-Makuch hopes this finding will bolster the belief that there could be life on Titan, but other astrobiologists have their doubts.
“It’s much ado about nothing, really,” says Jonathan Lunine of the University of Rome Tor Vergata in Italy. Unlike Titan, he says, Pitch Lake still has some water that the microbes could live in. “The hydrocarbon is the food. On Titan the hydrocarbon lakes replace the water. Very different.”
Chris McKay of the NASA Ames Research Center in Moffett Field, Calif., agrees. “It’s pretty clear that the microorganisms in this study are consuming the asphalt but living in liquid water,” he says.
The possibility that the Pitch Lake microbes live in hydrocarbon is a “more outlandish speculation,” Schulze-Makuch admits, “and probably less likely. But it’s still an option that we have to investigate.”
