Dining on Methane in the Cold, Dark Sea

This is Dr. Jennifer Glass, assistant professor, School of Earth and Atmospheric Sciences at Georgia Tech. Credit: Rob Felt

A new study supported in part by the NASA Astrobiology Institute is helping astrobiologists understand how methane-oxidizing bacteria survive in deep, cold water around methane seeps on the ocean floor.

Deep below the ocean, where temperatures are low and pressure is high, methane gets locked inside ice crystals called methane hydrates.

The study reveals previously unknown details about the process that two microbes (one bacteria and one archaea) use to ‘eat’ this methane. It all centers around the rare trace metal, tungsten. For the first time, scientists have identified a microbial tungsten enzyme that is used in this cold, dark environment.  Cold methane seep environments are much different than the boiling waters of hydrothermal vents where tungsten enzymes have been spotted before.

Typically, microbes use the more common metal molybdenum in cold environments. But for some reason, these microbes also use the scarce metals tungsten and cobalt.

"We don’t know exactly why the organisms seem to be making a protein that binds the rare element tungsten instead of the more commonly used molybdenum," said lead author Jennifer Glass in a recent press release from Georgia Tech.

Life in the Cold

Microbes that live in extremely low temperatures are known as psychrophiles or cryophiles. Psychrophilic microorganisms have been identified all over planet Earth, from the deep sea to high mountain peaks. The cold causes many challenges for life – such as decreases in the fluidity of membranes, reduced enzyme activity, and the formation of damaging ice crystals inside cells.

Psychrophiles need many unique adaptations to survive the cold. Studying these adaptations can help astrobiologists understand how life might survive on frozen worlds in our solar system, such as Mars.

Glass works in a chamber where she can control the oxygen levels to mimic the deep sea environment. Credit: Rob Felt

A story of Astrobiology and Climate

Methane hydrates represent a significant store of methane on Earth. Scientists have shown that these crystals can be an important source of energy for deep-sea microbial communities. However, some scientists also believe that methane hydrates could contribute to global warming in the future. As a result of global sea temperature rise, or events like earthquakes, the methane could be released from the sea floor and ultimately end up in our planet’s atmosphere.

The study was published in the journal Environmental Microbiology.

A mouthful of enzyme

The name of the enzyme that is used by the cold seep microbes is called formylmethanofuran dehydrogenase. This enzyme is involved in the last step of converting methane to carbon dioxide… and is essential for methane oxidation.

Jason being launched for an unrelated study in the Mediterranean Sea in 2011. Credit: Cherie Winner, Woods Hole Oceanographic Institution

Diving into the Dark

To study the microbes close up, the research team used the submersible Jason.

Jason plunged deep in to the ocean off the coasts of Oregon and California to explore the methane seeps in this study. Using its robotic arm, the submersible collected sediment samples that scientists later studied in the laboratory.

To see Jason in action, check out this video from the Woods Hole Ocean Institute where the submersible observes the eruption of an underwater volcano.

This video shows a hot hydrothermal system on the seafloor, which much different than the cold methane seep studied by Jennifer Glass and her colleagues. But the video is an example of how robotic explorers on Earth, such as the remotely controlled Jason submersible, can help astrobiologists study some of the most dangerous and difficult-to-reach environments on our planet.