Microbiologists have developed a new technique that can separate the DNA of living microbes from that of the dead.
The new life detection method has been tested in the extremely arid Atacama Desert in Chile and has the potential for use in other hostile environments, including on other planets.
The Atacama is the driest hot desert on Earth largely because it sits between two mountain ranges that each create a rain shadow. It has been arid since the Jurassic period, 150 million years ago.
The Atacama presents severe limitations on life with extremely low moisture and organic carbon coupled with high concentrations of salts, arsenic and UV radiation. Despite this, microbial communities survive even in the most marginal areas of the desert.
Interest in astrobiology prompted the detection of these microbes in the 1960s when NASA began planning to land the first Viking spacecraft on Mars. The Atacama was deemed to be the closest Earthly approximation of the Red Planet and thus the best place to test life detection methods.
The new life detection method published this week paves the way for more sensitive analyses on even small samples of living microbes. This includes metagenomics, the study of the structure and function of the DNA from microbial communities.
“Microbes are the pioneers colonizing this kind of environment and preparing the ground for the next succession of life,” says Dirk Wagner, a German geomicrobiologist who led the study.
Existing tools for extracting genetic material from soils capture DNA from both living and dead microbes, some of which could have died long ago. The new technique addresses this problem by separating the intracellular DNA (iDNA) found in intact living cells from the fragmented extracellular DNA (eDNA) left over from dead cells.
The method calls for multiple cycles of gentle rinsing to separate iDNA from eDNA. Wagner and colleagues say these steps concentrate high quality iDNA “which is often the bottleneck in low-biomass environments.”
The ratio of iDNA and eDNA from each species can also be a useful metric. “If a community is really active, then a constant turnover is taking place, and that means the 2 pools should be more similar to each other,” says Wagner.
Wagner and colleagues plan to apply the method in other hostile environments and leverage the higher quality iDNA for metagenomic analyses that target the active members of microbial communities.
The research is published in the journal, Applied and Environmental Microbiology.
