I just listened to a talk about a new astrobiology research project, whose aim is to probe the deep-subsurface biosphere, and it (the talk and the project) was pretty darned interesting, so I thought I’d share some notes.
I have to admit that I’m fond of microbial life. One of my favorite magazines is Microbe (published by the American Society for Microbiology). Also, I do science communication research for NASA’s astrobiology program, which keeps me immersed in science news about microbes. From Harvard’s Colleen Cavanaugh and others in the astrobiology community, I’ve learned that microbes are our friends…
Jan Amend gave the talk I heard at the Space Telescope Science Institute in Baltimore, Maryland, on April 25 this year. It was one in STScI ‘s ongoing astrobiology lecture series. Amend is a professor of Earth sciences and biological sciences in the Department of Earth Sciences at the University of Southern California (USC). He’s also principal investigator for a new team research project recently funded by the astrobiology program’s NASA Astrobiology Institute.
Here’s a brief introduction to the Amend team’s project: “On Earth, microorganisms appear to inhabit all physical space that provides the minimum requirements for life. These include the availability of water, carbon, nutrients, and light or chemical energy. While these are generally abundant in surface or near-surface environments, their mode and distribution in the subsurface are poorly constrained. Nevertheless, it has now been shown unequivocally that archaea and bacteria inhabit deeply buried rocks and sediments where they contribute to biogeochemical cycles. All evidence suggests that these subsurface ecosystems are spatially enormous and diverse. On other planets, at least in our solar system, putative extant or extinct life would most likely reside underground or in massive ice shells.”
You can read about Amend’s NAI team project here. You can read about Amend’s research and publications here and here. And if you’d rather watch Amend’s lecture (about an hour) instead of reading my blog post about it, you can do so here.
“This is my first NASA grant,” Amend told his STScI audience. “We are not NASA people, really.” However, building on his own research interests and experience and bringing together other experts, he and his team proposed a multi-year research project to NASA based on the following premise: if there is or ever was life on Mars, it’s most likely that any evidence of it would be beneath, not on, the surface.
Following from this premise, it makes sense to learn as much as we can about the terrestrial – or, as Amend calls it, “intraterrestrial” – subsurface biosphere as we can, to better prepare for seeking evidence of extraterrestrial subsurface habitability and life. Amend’s new NAI team will focus on terrestrial in-situ subsurface microbial life detection and characterization. “We are going to be hunting for new organisms,” he said.
By one reckoning published 15 years ago, (Whitman et al, “Prokaryotes: the unseen majority,” Proceedings of the National Academy of Sciences, June 1998), one third of Earth’s carbon biomass is subsurface – that is, in the rock beneath Earth’s surface (including the sea floor and sea-floor sediments). This vast environment is still largely unexplored and thus rich territory for the team to examine.
The Amend team plans to access the subsurface by way of existing boreholes, in deep mines such as the Sanford Laboratory (a repurposed mine in North Dakota), mines in Canada and South Africa, and at the Nevada National Security Site (a former weapons testing facility). They also plan to explore at deeply sourced springs, such as those in California’s Ash Meadows National Wildlife Refuge – so we can “bring the subsurface to us.” And they expect to have access to the sea floor through the National Science Foundation’s integrated ocean drilling program. Their intent is to characterize the subsurface environment at a number of sites.
So how deep is the subsurface biosphere? “We don’t know what that depth is or what defines that depth” – pressure, temperature, available nutrients, available pore spaces for microbes to inhabit are all possibilities, Amend said. The team is hoping that, in some places, “we will in fact go below the biotic fringe,” that is, below the lowest depths at which evidence of life has been found thus far. (The assumption is that beyond some as-yet-undetermined depth, the subsurface is abiotic – that is, devoid of life. We won’t know until we get there, and when we do, it’ll be difficult to prove a negative, that is, no life.)
A primary tool for the Amend team is a Subsurface Explorer for the Assessment of Life (SEAL) – a long, tubular structure that should be able to get 5 kilometers (3 miles) below the ocean floor, using an existing borehole. SEAL has been used before and will be upgraded for this project, outfitted with a set of specialized analytic tools including a deep ultraviolet (DUV) microscope – suitable for this project because DUV fluorescence is non-destructive (that is, it does not damage samples). Amend commented that this instrument could prove useful for in-situ analysis on planetary exploration mission missions, circumventing the challenge of returning samples to Earth for analysis. SEAL will also carry a high-definition video camera, among other things. He said his team would not have its in-situ instruments ready to deploy for subsurface exploration for another two years.
(Amend’s team includes Rohit Bhartia of NASA’s Jet Propulsion Laboratory, who, under a 2010 grant award from the NASA astrobiology program’s Astrobiology Science and Technology Instrument Development (ASTID) element, is developing a an instrument of interest to the team – a “Green and UV Raman Imager with Laser-induced Autofluorescence” (known as GURILA). Bhartia describes GURILA as a “next-generation instrument for mineral-organic mapping.” The aim is to develop a detection system that can “image organics at sub-parts-per-billion sensitivity.”)
In the world of microbiology, Amend said, gene sequencing has pushed aside cell culturing as the standard method of studying microbial life. However, “we realized that we had a lot of expertise and interest” in culturing at USC and the nearby California Institute of Technology, so Amend’s team plans to use novel culturing methods rather than sequencing. The team asserts that, of subsurface microbes deemed unculturable, “a significant number are not unculturable, but rather uncultured” – hence, their plans for “guided cultivation of intraterrestrials.”
One novel culturing platform they plan to use is a “down-flow hanging sponge reactor,” designed by Hiro Imachi of the Japan Institute for Marine-Earth Science and Technology (JAMSTEC), who is currently a visiting scientist at Caltech. This bioreactor provides a “porous substrate” for culturing slow-growing, low-energy microbes such as those found to inhabit the subsurface thus far. It provides “very slow delivery of nutrients and fluids and very high surface area” in a completely anaerobic environment, simulating many features of the subsurface (though, notably, not pressure). They also will be using instrumented chemostats for growing microbes with a controlled supply of nutrients. These continually stirred tank reactors are “quite simple in concept,” Amend said, “but difficult to operate.” Another novel culturing method they intend to use is “on-chip cultivation.” With microbes they can’t grow by other methods, this latter method will enable them “to study microbial energetics at the single cell level.”
For the education and public outreach component of their project, Amend’s team is working with the Institute of Multimedia Literacy at USC’s School of Cinematic Arts to develop a sixth-grade “virtual world” science game in which student gamers will “live” as subsurface microbes.
It all sounds like fun, and I’ll look forward to this team’s results. If you’re interested in learning more about the deep biosphere, you can check out another STScI astrobiology lecture, delivered last year by USC’s Katrina Edwards, who is a member of Amend’s NAI team.
In a future post, I’ll report on another new NAI team project, headed by Nigel Goldenfeld at the University of Illinois, Urbana-Champaign.