Thursday, 6 September 2018

Why bacteria survive in space


In professor George Fox's lab at the University of Houston, scientists are studying Earth germs that could be contaminating other planets. Despite extreme decontamination efforts, bacterial spores from Earth still manage to find their way into outer space aboard spacecraft. Fox and his team are examining how and why some spores elude decontamination.

To gain access into the uber-sanitized clean rooms at NASA's Goddard Space Flight Center in Greenbelt, Maryland, the world's largest clean room, or the Jet Propulsion Laboratory in Caltech, California, employees pass through a series of lobbies. One, with adhesive floor mats, traps dirt carried on shoes. Another, about the size of an old phone booth, delivers a forced-air shower where dozens of air jets blow away dirt and debris. Only after these sterilization measures can they don the bodysuits, head covers and other disinfected regalia.

And still, bacteria survive and have been carried onboard the International Space Station and found on the Mars Rover. The ability of bacteria to survive extreme conditions could potentially lead to a process called 'forward contamination.'

As with natural selection, the cleaning process inside clean rooms will eventually kill off the weaker bacteria while a stronger strain adapts and is unphased by the cleansers.

The Fox team studied non-pathogenic (non-disease-causing) bacteria that belong to the genus Bacillus and produce highly resistant spores. They were isolated from cleanrooms and spacecraft assembly facilities at the Jet Propulsion Laboratory.

They sequenced the complete genome of two strains resistant to peroxide and radiation: B. safensis FO-36bT and B. pumilus SAFR-032. Then they compared the genomes of those strains and that of another strain, B. safensis JPL-MERTA-8-2, with bacteria known to produce spores that are vulnerable to peroxide and radiation, such as the strain B. pumilus ATCC7061T. The B. safensis JPL-MERTA-8-2 strain was isolated from the Mars Odyssey Spacecraft and associated facilities at the Jet Propulsion Laboratory and later also found on the Mars Explorer Rover (MER) before its launch in 2004.

By comparing the blueprints of the four strains, they found 10 genes that are unique to the FO-36b, that are not found in any other organisms (including other Bacillus strains). That is 10 genes whose functions are unknown -- or 10 suspects for why spores of B. safensis FO-36bT are resistant to peroxide and radiation, although it is not immediately obvious that the presence or absence of any specific gene or combination of genes is responsible for the variations in resistance seen.


As it turns out, four of these genes are found on phage elements of the bacterial strain. Phage, short for bacteriophage, is a virus that infects bacteria. Phages are major facilitators for transferring genes between microbes.

For details see:

Madhan R. Tirumalai, Victor G. Stepanov, Andrea W√ľnsche, Saied Montazari, Racquel O. Gonzalez, Kasturi Venkateswaran, George E. Fox. Bacillus safensis FO-36b and Bacillus pumilus SAFR-032: a whole genome comparison of two spacecraft assembly facility isolatesBMC Microbiology, 2018; 18 (1) DOI: 10.1186/s12866-018-1191-y

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology

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