If humankind is to explore deep space, one small passenger should not be left behind: microbes.
In fact, it would be impossible to leave them behind, since they live on and in our bodies, surfaces and food. Learning how they react to space conditions is critical, but they could also be invaluable fellows in our endeavor to explore space.
Microorganisms such as bacteria and fungi can harvest crucial minerals from rocks and could provide a sustainable alternative to transporting much-needed resources from Earth.
Researchers from Cornell and the University of Edinburgh collaborated to study how those microbes extract platinum group elements from a meteorite in microgravity, with an experiment conducted aboard the International Space Station. They found that "biomining" fungi are particularly adept at extracting the valuable metal palladium, while removing the fungus resulted in a negative effect on nonbiological leaching in microgravity.
Rosa Santomartino, assistant professor of biological and environmental engineering in the College of Agriculture and Life Sciences, prepares samples for the launch to the International Space Station.
The team's study was published Jan. 30 in npj Microgravity. The lead author is Rosa Santomartino, assistant professor of biological and environmental engineering in the College of Agriculture and Life Sciences; Alessandro Stirpe, a research associate in microbiology, is a co-author.
The BioAsteroid project, which was led by senior author Charles Cockell, professor of astrobiology at the University of Edinburgh and included other University of Edinburgh researchers, used bacterium Sphingomonas desiccabilis and fungus Penicillium simplicissimum to see which elements could potentially be extracted from L-chondrite asteroidal material. But understanding how the microbes interact with rocks in microgravity was equally important.
"This is probably the first experiment of its kind on the International Space Station on meteorite," Santomartino said. "We wanted to keep the approach tailored in a way, but also general to increase its impact. These are two completely different species, and they will extract different things. So we wanted to understand how and what, but keep the results relevant for a broader perspective, because not much is known about the mechanisms that influence microbial behavior in space."
These microbes are promising tools for resource extraction because they produce carboxylic acids, the carbon molecules which can attach to minerals via complexation and spur their release. But many questions remain about how this mechanism works, according to Santomartino, so the team also conducted a metabolomic analysis, whereby a portion of the liquid culture is collected from the completed experiment samples and the researchers examine the biomolecules contained, specifically the secondary metabolites.
NASA astronaut Michael Scott Hopkins performed the ISS experiment, to test microgravity, while the researchers conducted their own control version in the lab, to test terrestrial gravity and compare these with the space results. Santomartino and Stirpe then analyzed the voluminous amount of data that was collected, which comprised 44 different elements, of which 18 were biologically extracted.
"We split the analysis to the single element, and we started to ask, OK, does the extraction behave differently in space compared to Earth? Are these elements more extracted when we have a bacterium or a fungus, or when we have both of them? Is this just noise, or can we see something that maybe makes a bit of sense? We don't see massive differences, but there are some very interesting ones," Stirpe said.
The analysis revealed distinct changes in microbial metabolism in space, particularly for the fungus,which increased its production of many molecules, including carboxylic acids, and enhanced the release of palladium, as well as platinum and other elements.
For many elements, nonbiological leaching - in which a solution without microbes is used to pull out the elements - was less effective in microgravity than on Earth. Meanwhile, the microbes had consistent results in both settings.
"In these cases, the microbe doesn't improve the extraction itself, but it's kind of keeping the extraction at a steady level, regardless of the gravity condition," Santomartino said. "And this is not just true for the palladium, but for different types of metals, although not all of them. Indeed, another complex but very interesting result, I think, is the fact that the extraction rate changes a lot depending on the metal that you are considering, and also depending on the microbe and the gravity condition."
In addition to aiding space exploration, applications could have terrestrial benefits, such as efficient biomining from resource-limited environments or mine waste, or creating sustainable biotechnologies for circular economy. Santomartino cautions that while the biotechnology community is eager to learn the exact impact that space has on microbial species for this purpose, a tidy explanation may not be forthcoming. There are just too many variables.
"Depending on the microbial species, depending on the space conditions, depending on the method that researchers are using, everything changes," Santomartino said. "Bacteria and fungi are all so diverse, one to each other, and the space condition is so complex that, at present, you cannot give a single answer. So maybe we need to dig more. I don't mean to be too poetic, but to me, this is a little bit the beauty of that. It's very complex. And I like it."
The research was supported by the United Kingdom Science and Technology Facilities Council, the Leverhulme Trust, the University of Edinburgh School of Physics and Astronomy and Edinburgh-Rice Strategic Collaboration Awards.
