Anna-Louise Reysenbach is searching the sea floor for clues about life on Earth and beyond.
Most people would probably be intimidated by the thought of stepping into a cramped submersible, diving a mile or two below the ocean surface, and hunting the freakish microbes that thrive on scorching hydrothermal vents.
For microbiologist Anna-Louise Reysenbach, a professor at Portland State University, it’s all part of the adventure of researching these tantalizing deep sea habitats, where otherworldly creatures shed light on the history of life on Earth—and perhaps, elsewhere in the universe.
“I was always fascinated by the natural world as a kid,” Reysenbach told me over Skype. “I decided that you spend most of your life at work so you might as well do what you love, and I just loved being around water.”
“Deep sea vents and these weird new lifeforms were being discovered as I was finishing my PhD [at the University of Cape Town], and I was just so fascinated by life in extreme environments and the unknown,” she added.
Hydrothermal vents are fissures in the ocean floor, created by tectonic and volcanic activity. Scalding water, sometimes hotter than 400 degrees Celsius (752 degrees Fahrenheit), bubbles up through these cracks, spewing out chemicals like iron, carbon dioxide, and hydrogen sulfide into the marine environment.
It doesn’t seem like the type of habitat that would be conducive to life, and yet rich ecosystems of extremophile organisms have devised ingenious ways to survive these sweltering conditions. Reysenbach is interested in the tiny creatures that form the bedrock of such deep sea food webs, including Archaea, microbes that may have been the first life to appear on Earth.
Not all Archaea live at these ocean vents: Reysenbach mentions she is currently studying an organism related to the symbiotic archaeon Nanoarchaeum equitans found in hot springs, like those in New Zealand, which she calls the “coolest little bugger.”
But for those organisms that do live in the deep, far from the reach of sunlight, photosynthesis is not a viable means of energy. Instead, microbes power themselves via their geothermal, carbon-rich environment, in a process called chemosynthesis.
Reysenbach and her colleagues have been able to collect some of these idiosyncratic beasties and nurture them in the laboratory, using heated water habitats. “We often successfully grow things that have never been grown before, and that to me is very exciting,” she said. “We get to study them a little more deeply. We can figure out what exactly they’re doing, and how they’re functioning in the environment.”
This is important for contextualizing the history of life on Earth, but it could potentially help scientists identify alien organisms on other worlds. Earlier this year, a study published in Science presented compelling evidence that hydrothermal activity is present on Saturn’s moon Enceladus, and Jupiter’s ice moon Europa is also suspected to harbor deep sea vents.
“If we’re looking for the same kind of life on places like Enceladus, we can only look for what we know,” Reysenbach said. “But what working with these extremophiles has also taught us is that we are sometimes very surprised to find things we didn’t expect. It keeps your eyes open to other possibilities of the way life can exist.”
In addition to these insights, genome sequencing technologies have become so advanced over the last decade, that it’s now possible to dismantle the DNA of a sample containing several microbial species into elemental pieces, then reassemble them correctly using sophisticated algorithms, like a puzzle. This process has provided a much more thorough understanding of these organisms’ evolutionary history, and their place in the tree of life.
“It’s absolutely wild,“ Reysenbach said of the genomic revolution. “What we’re finding is much greater diversity than we ever expected at these deep sea vents.”
These creatures and their extreme adaptations have a range of potential uses in medicine and technology, given their ability to metabolize chemicals in harsh conditions. Some Archaea species have already been deployed in metal mines to help extract residual resources. But given how little we know about deep sea microbes, it’s hard to predict what kind of future impact they might have on human life and technologies.
“We haven’t explored a lot of the deep ocean,” Reysenbach said. “There’s still a lot to be discovered. Understanding the function and role of these microbes, and looking at them in their environment and in the lab, is where a lot of this research has to go.”
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