MICROBIOLOGY
While James Cameron may not have seen many life-forms in the Challenger Deep, expedition scientists have confirmed that the oceans’ deepest places are crawling with one particular type of life: microbes. These single-celled creatures interest researchers because of their ability to thrive in an extreme environment. Locked in their cell walls could be insight into everything from the origins of life to cures to diseases.
ORIGINS OF LIFE?
At 35,100 feet (10,700 meters) deep, the expedition captured images of rocks covered in a stringy substance—something like hair dipped in soup, one scientist observed. But where ordinary people might see rocks sporting dirty beards, researchers see possible clues to the origins of life.
The stringy rock coatings, more technically called microbial mats, represent clumps of single-celled organisms. Expedition researchers found the mats after they dropped a sampling and imaging device into the waters of the Sirena Deep, an area in the Mariana Trench east of the Challenger Deep. Chief expedition scientist Doug Bartlett said they have been able to determine that these cells have the genes to fix carbon dioxide in the dark and to feed off of reduced sulfur.
Scientists have found similar mats before but never this deep. These cells provide more data that could be used to support an emerging theory that life could have begun in areas not unlike the modern-day Mariana Trench. At plate boundaries like the Mariana Trench, where one plate subducts beneath another, a mineralogical process called serpentinization releases methane and hydrogen. Those gases, some scientists argue, could have provided the first energy sources for life to evolve. That life could have been cells not unlike those found in the Sirena Deep’s microbial mats.
THOUSANDS OF MICROBES
During the expedition, tens of thousands of microbes were collected in a number of ways, some via water samples, others via sediment samples. Still others were captured by slicing open the creatures that host them, specifically amphipods, shrimp-like deep-sea dwellers. One bacteria found in the amphipods gathered in the New Britain Trench matched a type of bacteria found in the faraway Puerto Rico Trench, leaving scientists to puzzle over how—or if—a deep-sea-loving organism managed to land in different “islands” of incredible depth.
Bartlett originally stored thousands of deep-sea microbes in dozens of steel cylinders. Holding anywhere from 10 milliliters to half a gallon (two liters), these canisters provided the cold, dark, high-pressure environment that the microbes associate with home. Since the expedition, Bartlett and his team have been doing the painstaking work of isolating particular species—the researchers can open up the cylinders for brief periods of time, but if the cells are left in atmospheric pressure for too long, they could die. Once all of the species were separated, they looked at their morphology, their chemical makeup, and other characteristics to figure out what allows these organisms to grow at high pressure, what they’re eating, and what life is generally like for the tiniest life-forms in the most remote areas of the planet. Fatty acids are of particular interest because the membranes of many deep-sea bacteria contain the omega-3 polyunsaturated fatty acids that are known to be very heart healthy for humans. Scientists are also intrigued by the possibility that they could feed not just from organic particles raining down through the ocean, but also from substances within the Earth’s mantle.
Microbes that weren’t cultured have had their DNA amplified, which led to the identification of more than 70 new species. Bartlett and his team are hoping that sequencing the microbial DNA provides further clues about the organisms’ evolution and physiology. They’re also looking to compare these deep-sea dwellers with life from other parts of the world’s ocean.
