Earth microbes could contaminate space samples, researchers say

Scientists studying “clean” labs in which extraterrestrial objects ranging from meteorites to Moon rocks are stored have found that these facilities may not be quite as clean as they thought. This raises concerns for when Japan’s Hyabasu-2 and NASA’s OSIRIS-REx missions bring back samples from two asteroids in 2020 and 2023.

As scientists search for life on Mars and other worlds, one of the biggest concerns has been ensuring that we don’t contaminate them with bacteria hitchhiking from Earth on spacecraft and landers. 

But the reverse also applies: we need to make sure that the same organisms don’t contaminate samples brought back from other worlds. 

Not that there’s a risk of them being mistaken for ET, but these organisms can alter the chemistry of samples, making it difficult to determine whether chemicals found in them actually originated in space, says Aaron Regberg, a geomicrobiologist at NASA’s Johnson Space Flight Centre in, Houston, Texas, US.

For example, he says, “there are whole suites of amino acids that have been identified in carbon-rich meteorite samples, which are relatively rare on Earth. [But] you have to convince yourself that the compounds were originally part of the meteorite and not added later.”

Bacterial contamination has long been recognised as a concern, but it turns out that fungi are also an issue. In a paper presented at the Lunar and Planetary Science Conference in The Woodlands, Texas, Regberg said he was surprised by the variety and number of fungi found growing in NASA’s Meteorite Lab — a facility that isn’t a top-end clean room but which is designed to minimise contamination from materials such as trace metal contaminants or other environmental pollutants. Such labs “are kept very clean,” he says. 

Fungi are an important overlooked source of contamination, he says, because they are capable of producing exotic amino acids. Because these are not produced by most Earth life, they are sometimes “targets of investigation” for researchers looking to determine the production of amino acids in space. But if they can also be produced by moulds living in the labs or on the samples, he says, that’s something important not only to know, but to avoid. 

Some examples of fungi that can create such amino acids are species in the genus Penicillium, some of which also produce the antibiotic drug penicillin. Such moulds, Regberg adds, were indeed found in his study, although not the varieties known to produce exotics. Still, it’s a warning that clean rooms — and by implication, space rocks — can easily be contaminated by fungi that could ruin important lab tests.{%recommended 6243%}

It’s easy, of course, to solve this by making sure that all samples brought back by Hyabusa-2, OSIRIS-REx, or a future Mars sample return are treated in ways that ensure that they are free of fungi or other microorganisms. “As microbiologists, we know how to keep things sterile,” Regberg says. 

The question is how to do that without ruining the sample in the process, by chemically altering it. For example, a standard method of sterilising materials is by autoclaving – baking them at a high temperature. This, in fact, is what is done with external surfaces of Mars rovers and similar equipment. 

But Regberg says, “no one is going to let me autoclave samples. Nor do I want to. We have to have a conversation about what steps we can take without causing a new problem.”

Regberg’s fungi, however, don’t appear to pose an additional risk for accidentally carrying Earth life to Mars or other exploration sites. That’s because Mars-bound hardware is better able to withstand autoclaving than space rocks, and the processes designed to kill off any bacteria on them are also “pretty effective” at killing fungal spores. 

“They’re not as resistant to heat as bacterial spores,” Regberg says. “But if you sent people, that’s a different story.”

Even that, however, might not be as big a concern as once believed, says another study, led by Andrew Schuerger of the University of Florida. 

Schuerger could not be reached for comment (and did not appear in Houston to present his study), but according to the conference abstract, his team studied microbiological samples from a simulated Mars base on Devon Island in the Canadian Archipelago, used each summer since 2000 as an analogue for human habitats in the cold desert of Mars.

Schuerger’s study focused on human “commensal” bacteria and fungi (ones that normally life in our gut, mouth, or skin), looking to see how far they spread from living spaces, latrines, and mess hall tents. The results are preliminary, but found that these microorganisms are not easily dispersed under Devon Island conditions, which are actually somewhat less extreme for Earth life than those on Mars. 

“If confirmed, these results may indicate that human habitats on Mars will not overly contaminate the local terrains surrounding the landing sites,” he wrote.