As unbelievable as it sounds, it's thought that up to a third of all the Earth's organisms by mass live in rocks and sediments. Suffice to say, we know excruciatingly little about the lives and ecology of these highly inaccessible creatures. But a new study from the University of Massachusetts Amherst is offering an unprecedented glimpse into these extremophiles — including a methane-exhaling microbe that dwells deep inside the cracks of active undersea volcanoes.
Given how hard it is to discover and study microorganisms that live deep inside of rocks, a number of biologists have focused their efforts on exploring hydrothermal vents at undersea volcanoes. And this makes good sense: Warm water flows bring nutrients and energy sources directly to the microbes, allowing them to live near the rock-ocean barrier. Biologists are thus able to observe these microbes in their actual habitat, offering an unprecedented opportunity to better understand the biogeochemical cycles of the deep ocean.
The study, which was led by microbiologist James Holden, also addressed the question of what metabolic processes might have looked like on Earth about three billion years ago — and what microbial life might look like on other planets.
And indeed, the timing of the paper is actually quite interesting given the recent landing of the Curiosity rover on Mars. Holden's study describes a kind of microbe called a "methanogen" — an organism that inhales hydrogen and carbon dioxide to produce methane as waste. It just so happens that Curiosity will be measuring Mars for its methane content — a possible indicator of habitability. Should the presence of methane be confirmed, NASA scientists will undoubtedly be interested in Holden's study.
As for the methane-exhaling microbes themselves, Holden's team used computer models to predict environmental thresholds, and whether there was sufficient hydrogen for their needs (specifically, they need at least 17 micromolar of hydrogen to grow). The models indicated yes, but the researchers wanted to see it with their own eyes.
To that end, they used the research submarine Alvin and traveled undersea to collect samples of hydrothermal fluids flowing from black smokers up to 350 degrees C (662 degrees F). Samples were taken from the Axial Volcano and the Endeavour Segment and then sent to labs for detailed chemical and biological analysis — a process that involved teams from several institutions.
The results confirmed the lower threshold of hydrogen concentration needed by these microbes. They also discovered that the metabolic requirements and processes of the microbes varied significantly depending on their exact location at the vents. And fascinatingly, the researchers uncovered a kind of extreme heat-loving methanogen that was completely dependant on the hydrogen waste produced by other hyperthermophiles, and vice-versa — a strong indication that these organisms live in highly complex ecosystems.
The results of the study are set to appear in an upcoming issue of Proceedings of the National Academy of Sciences.
Top image via pmel.noaa.gov. Inset image via University of Massachusetts Amherst.