Deep below the ocean, within and on the ancient sediments and rock that interface with the very core of our planet, there are microbes. How do these microbes survive? What are their impacts on life on Earth? Katrina Edwards, Ph.D., (1968-2014), spent her career trying to find out. Known as the “Mistress of the Dark World,” Edwards was a pioneering scientist whose leadership, discoveries and mentorship were foundational to unlocking the mysteries of microbial life in the “deep biosphere”—and fostering a community of scientists who continue to shine light on a part of the microbial world that never sees any.  

From the Skies to the Sea

A native of Columbus, Ohio, Edwards didn’t start her career peering into the watery depths of the ocean. Rather, she had her eyes trained on the sky. After graduating high school, Edwards worked at her family’s municipal airport in Ohio, assisting with general airport operations before eventually becoming a chief flight instructor.  

It was during college at The Ohio State University that Edwards honed in on the craggy wonders of the Earth’s surface. Alongside her job at the airport, she pursued a bachelor’s degree in geology, graduating with honors in 1994. Edwards went on to obtain a master’s degree in isotope geochemistry from the University of Wisconsin Madison (UW-Madison) and a Ph.D. from the same institution in 1999. Her doctoral work centered on geomicrobiology (i.e., the study of interactions between microbes and earth materials). In this regard, microbes can do everything from metabolizing rocks and minerals to conducting electricity via electron transfer reactions with earth surfaces. Studying these interactions tells scientists not only about the breadth of microbial diversity and functions on Earth, but also how these microbes influence the geology and elemental cycles of the planet.

While studies in geomicrobiology had been taking place for years, it wasn’t until the work of a growing group of scientists in the late 1990s-early 2000s, with Edwards among their ranks, that the discipline started to take off. In fact, Edwards received the first degree awarded by UW-Madison in the discipline, foreshadowing her role as a leader in the field. 

After graduate school, Edwards joined the Woods Hole Oceanographic Institute (WHOI) as an associate research scientist. There, she established a geomicrobiology lab to examine what she called the “tooth decay of the solid Earth” (i.e., microbial degradation or transformation of earth materials and organic matter), including investigating iron-oxidizing bacteria surrounding the Loihi Seamount (an active underwater volcano in Hawaiʻi) and their effects on ocean chemistry and ecosystem function. Edwards’s tenure at WHOI solidified her focus on microbial life inhabiting the ocean floor. And, as a professor in the departments of Biological Sciences and Earth Sciences at the University of Southern California Dornsife College of Letters, Arts and Sciences, she only looked deeper. 

Investigating the Intraterrestrials

The more researchers learn about the microscopic inhabitants of our planet, the clearer it becomes that microbes are seemingly everywhere—even at the bottom of (and miles below) the ocean floor. Scientists estimate that roughly 15% of Earth’s biomass lives underneath the ocean floor, though for a long time they didn’t know much of anything about these subsurface microbes.

Edwards changed that. She was instrumental in developing the facet of geomicrobiology that deals with the deep biosphere. “If you think about the bottom of the ocean, and that is a big if, you probably think of 1 of 2 settings: abyssal, wafting plains of sediments or smoking hot hydrothermal vents,” Edwards said in a 2010 interview. “What lies in-between—hundreds of square kilometers in aerial extent, down kilometers below the ocean bottom, lies an active, living intraterrestrial ecosystem—this is what I think about almost all of the time.” 

Why study these so-called “intraterrestrials?” For one, the metabolisms of these microbes shape key elemental processes. “The seafloor is the ultimate home for all of the sediments [and] carbon that are created in the oceans,” explained Jason Sylvan, Ph.D., an associate professor of oceanography at Texas A&M University and former postdoctoral fellow in Edwards’ lab. “So, for understanding the fate of carbon, which is tied to climate change and global carbon cycles, it's important to understand what happens once that material reaches the seafloor. The deep biosphere [has] a quantifiable impact on ocean chemistry.”

Beth Orcutt, Ph.D., Vice President for Research and a senior research scientist at the Bigelow Laboratory for Ocean Sciences, and who was also a postdoc in Edwards’ lab, noted that insights into the lifestyles of deep-sea microbes could also help advance human health. These organisms eke out a living with little energy and are actively evolving to thrive in inhospitable environments. “Learning how microbes can survive on low energy enables us to learn things about, for instance, pathogenic microbes [that] end up causing disease,” some of which also live in cryptic ways, she said. It also allows scientists to explore where the genetic foundations for different microbial chemical processes come from. “If you really are excited about the novelty of microbes, then this is the place to go look for them,” Orcutt added.

However, to study the deep biosphere is to venture into unknown territory—to do it effectively and efficiently, one needs a solid team of researchers with varied expertise, from engineering to microbiology. It was with this understanding that Edwards spearheaded the project that would cement her scientific legacy.  

Advancing Deep Sea Microbiological Research

Edwards’ project—the Center for Dark Energy Biosphere Investigation (C-DEBI)—was more of a hub for many projects. Backed by a grant from the National Science Foundation (NSF), and with Edwards as its founder and inaugural director, C-DEBI aimed to interrogate interactions between microbes, rocks, minerals and geochemical fluids beneath the ocean floor. Its key mission was to “grow a field” of deep-sea microbiological research said Orcutt, who helped draft the C-DEBI grant as a postdoc and was heavily involved in its activities over the years. 

Though based at Edwards’ home institution, USC, C-DEBI was a partnership among 8 institutions across the U.S. The center also supported research at 45 additional institutions, with study sites spanning the world’s oceans. Over the course of its 12-year run (2010-2022), researchers involved with C-DEBI published 450 peer-reviewed papers, advanced technology to allow for greater study of the deep biosphere and provided new insights into the subseafloor environment and the microbial communities that live there. 

Cultivating a Community of Deep Biosphere Researchers

Perhaps one of C-DEBI’s greatest contributions is the community of deep biosphere experts it nurtured—a community that, without Edwards, would not exist. “[She] saw that if we're going to make a difference and understand life in the subsurface, we have to have more people involved,” Orcutt said. Sylvan agreed, noting how Edwards “was really good at bringing people from different backgrounds together to work on big ideas.” In some ways, C-DEBI was an institutional reflection of Edwards herself—a scientist with expertise in diverse fields (e.g., geochemistry, mineralogy, microbiology, oceanography and more). 

“What was special about [Edwards] was that she had a great understanding of both the geological and microbiological aspects of processes in the environment. Not only that, but she also understood the people behind the science. This is why she was such a natural leader,” said Roman Barco, Ph.D., an assistant research professor at USC Dornsife and former graduate student and postdoc in Edwards’ lab. 

The deep biosphere research community now has a new home base—the Crustal Ocean Biosphere Research Accelerator (COBRA). This virtual international network of researchers, with Orcutt as its co-director, focuses on delineating the structure, function, resilience and ecosystem service of the crustal ocean biosphere to inform decision-making. COBRA signifies a shift in the focus of deep-sea researchers toward using knowledge gained from years of study—largely motivated by Edwards—to inform action.  

Mentoring the Next Generation of Scientists

A central component of both C-DEBI, and now COBRA, was to train the next generation of deep-sea scientists—something that was foundational to Edwards pursuits and legacy. She directly mentored numerous students and postdocs in her lab, many of whom have gone on to lead their own careers in deep sea microbiology, including Sylvan, Orcutt and Barco. All 3 scientists tie their success back to Edwards in some way.  

“I was extremely lucky to have a mentor so respectful of students’ ideas and independence and at the same time provide enough direction, kindness and encouragement for the student to succeed and not feel alone in a process that is so individualistic sometimes,” Barco said. 

Sylvan noted that “[Edwards] was this amazing big thinker. She had this way of presenting [ideas] and convincing you to come along for the ride,” a trait he strives to bring to his own work as a scientist and mentor. Orcutt was similarly grateful, reflecting on the doors Edwards opened and her determination to support the people she committed to mentoring. 

Even now, almost a decade after her death, Edwards work continues to pave the way for young scientists to explore the deepest reaches of Earth’s oceans. “What I hope people take away from learning about [Edwards] and her work is that she was a brilliant person with a vision for the community, a fearless leader. We can give her credit for inspiring a new generation of scientists to study the deep biosphere,” Barco said.  

Edwards has even inspired those outside the deep biosphere field—or the research community in general—such as Sophia Dakkuri, an undergraduate arts major at Novia Scotia University who chose Edwards as her favorite microbiologist as part of ASM’s 2022 Agar Art Contest. Dakkuri noted that, despite her artistic pursuits, she has had a lifelong fascination with marine biology. When she was researching scientists for the contest, Edwards immediately caught her eye. “What I found most remarkable about her was how she had a passion for microorganisms that live below the sea level,” Dakkuri said. “From [Edwards’] work, we now understand the roles that these [subsurface] microbes have,” and how they may influence other life on the planet.

Without question, Edwards’ scientific contributions were exemplary, and she was recognized with various awards and fellowships during her career, including being elected as a fellow of ASM’s American Academy of Microbiology in 2010. Yet, those who worked with her remember her not just for her work, but for her sense of humor, creativity and enthusiasm. “There was literally a twinkle in her eye,” Sylvan said. “She was always excited about science and willing at the drop of a hat to share that excitement with almost anybody.” Edwards may have spent her time studying environments that are incredibly dark, but she was, and continues to be, a bright light. 

---

To learn more about Katrina Edwards, and other pioneering women microbiologists, check out Women in Microbiology by ASM Press.