The hunt is on to find why some bacteria survive in space
Despite stringent decontamination, NASA still sends germs aloft. Discovering how they survive is becoming increasingly urgent. Fiona McMillan reports.
Some microbes can resist decontamination before space flight, but this may not be because they are armed with additional genes to those of closely related strains.
Instead, new research in the journal BMC Microbiology suggests that commonly shared genes confer resistance because they act differently.
As interplanetary exploration increases, so too does the need to more effectively sterilise spacecraft in order to avoid contaminating other planets with Earth germs.
“The search for life elsewhere is impacted by the possible transport of organisms from Earth to solar system bodies of interest,” says George Fox of the University of Houston, who led the current study.
In fact, current rovers on Mars are most likely carrying Earth bacteria, and the Curiosity rover has had to carefully navigate areas where water might be flowing on Mars in order to avoid contaminating it.
It’s not that grimy tech was casually sent to the red planet, but rather that certain terrestrial microbes are stunningly tenacious.
For example, to gain entry to the clean rooms at the NASA Jet Propulsion Laboratory (JPL) at the California Institute of Technology, one must pass through a series of decontamination lobbies involving adhesive floor mats and forced-air showers before the donning disinfected body suits. Equipment decontamination is even more severe, and includes ultraviolet irradiation and cleaning with hydrogen peroxide. Very few microbes survive this – but some certainly do.
“No matter what we do, some bacterial spores appear to be finding ways to escape decontamination,” says the paper’s first author Madhan Tirumalai, who works with Fox at the University of Houston in the US.
“I’m trying to understand what makes these spores so special at their genomic level and relate these features with their ability to evade decontamination measures,” he says.
Fox, Tirumalai and their colleagues sequenced the complete genomes of two strains of Bacillus bacteria isolated from cleanrooms at JPL. Both produce decontamination-resistant spores: B. safensis FO-36bT and B. pumilus SAFR-032.
The genomes were compared with that of a known decontamination-resistant strain, B. safensis JPL-MERTA-8-2, and all were compared to a Bacillus strain known to be vulnerable to peroxide and UV irradiation.
The decontamination-resistant strains were found to share 59 genes that were not present in the vulnerable strain. However, a broader search revealed that each of these genes could be found in least one other strain of Bacillus, meaning they weren’t that unique after all.
Although many of those other strains are from environments with some kind of stress component, such as soil contaminated with heavy metal, it was unclear if any involved resistance to UV or peroxide.
The robust B. safensis FO-36bT strain did have 10 unique open reading frames (ORFs), which could be genes for as yet unknown proteins, that were not shared with other bacteria. Interestingly, a handful of these appear to be viral DNA incorporated into the bacterial genome. So it would seem that although the bacteria strains in this study were highly similar, their variation is due in part to latent infection with bacteriophage viruses.
Nevertheless, it remains unclear whether any of these potential genes are responsible for resistance to decontamination. Nothing stood out as a possible culprit.
The researchers propose that resistance to decontamination could instead be the result of changes in gene activity.
“It is quite possible that distinctions in gene regulation can alter the expression levels of key proteins thereby changing the organism’s resistance properties without gain or loss of a particular gene,” says Tirumalai.
The next step will be to take a closer look at which genes are being turned on and off in space-hardy microbes.