Tuesday, December 22, 2015

Does Very High Dessication Tolerance Increase Radiation Resistance in Microbes?

Isolation of Radiation-Resistant Bacteria from Mars Analog Antarctic Dry Valleys by Preselection, and the Correlation between Radiation and Desiccation Resistance


Musilova et al


Extreme radiation–resistant microorganisms can survive doses of ionizing radiation far greater than are present in the natural environment. Radiation resistance is believed to be an incidental adaptation to desiccation resistance, as both hazards cause similar cellular damage. Desert soils are, therefore, promising targets to prospect for new radiation-resistant strains. This is the first study to isolate radiation-resistant microbes by using gamma-ray exposure preselection from the extreme cold desert of the Antarctic Dry Valleys (a martian surface analogue). Halomonads, identified by 16S rRNA gene sequencing, were the most numerous survivors of the highest irradiation exposures. They were studied here for the first time for both their desiccation and irradiation survival characteristics. In addition, the association between desiccation and radiation resistance has not been investigated quantitatively before for a broad diversity of microorganisms. Thus, a meta-analysis of scientific literature was conducted to gather a larger data set. A strong correlation was found between desiccation and radiation resistance, indicating that an increase in the desiccation resistance of 5 days corresponds to an increase in the room-temperature irradiation survival of 1 kGy. Irradiation at −79°C (representative of average martian surface temperatures) increases the microbial radiation resistance 9-fold. Consequently, the survival of the cold-, desiccation-, and radiation-resistant organisms isolated here has implications for the potential habitability of dormant or cryopreserved life on Mars

1 comment:

3de8af9a-85a1-11e4-b784-0b02f2c1f23a said...

Well... the answer to the title is actually really cool--more so then this study implies. It's been long established that dessication resistance == radiation resistance (not just for bacteria, but also small organisms like the water bear). Not only that, but we know molecularly -how- and -why-. All this first mostly discovered from the Deinococcus genus of bacteria, and then generalized among others (particularly radiodurans). Deinococcus can take around 6 kGy of radiation (or over a month of dessication) with nearly 90% survival, at room temp, due to manganese hoarding which protects the protein content of the cell from ionization, and specialty, advanced double strand break DNA repair enzymes that leverage the multiploidy nature of the bacterial genome to repair via really clever error checking mechanisms (like ECC RAM or harddrives in RAID 1). Giving either of these systems to say E. coli significantly increases it's radiation -and- dessication resistance upwards towards an order of magnitude. It's pretty wild, and has been looked at in regards to astro- and xenobiology implications for awhile now. On the flipside, removing these pathways from Deinococcus pretty well eliminates it's radiation -and- dessication resistance.

This study is cool due to where they looked, more than anything--finding similar bacteria in a more Martian like setting (though of course not actively alive in a frozen state). Very good news for terraforming prospects, with a bit of genetic engineering.