Life in the Rocks: Cold Version

I vicariously followed the adventures of Tullis Onstott and his colleagues in Chapter Nine of Deep Life. Nunavut, Canada, is cold, cold, cold. Could there be life down in the rocks below the permafrost? If so, it might tell us how to hunt for life on Mars below its barren surface. While I mentioned the challenges of field work in my previous blog post, and how I am ill-suited to undertake such arduous, reading about it is exciting. I recommend Deep Life for the blow-by-blow accounts.

 

In this icy cold chapter, the scientific team successfully isolates a prokaryote that makes its living via chemolithoautotrophy. That’s chemistry in the rocks where you make your own food by using energy from the redox gradient from rock chemistry. The autotrophs we are most familiar with are green plants which are photoautotrophs. They make their own food with energy streaming down as photons from the sun. Trying to determine what this microorganism does or how it makes its living is challenging. You have to chop up its DNA, determine its sequence, then try and match it up to known sequences that code for proteins that do biochemistry you’ve seen before.

 

They got to name their organism: Desulforudis audaxviator. It lives through reduction of sulfur compounds (desulfo), it is rod-shaped (rudis), and it is a ‘bold traveler’ (audax viator) thanks to having genes that indicate flagella for motility. They even have a scanning electron microscope picture (read the book!). But what was shocking is that it also had the genes for a complete nitrogen-fixation pathway. That’s very expensive biochemically. Were these just a relic or does the microbe use them? I don’t know. It’s acetyl-CoA pathway also resembled that found in archaea. That’s of interest to me in relation to my origin-of-life research.

 

The author has a great cartoon picture (shown above) showing its potential biochemistry from the sequencing data. They have the audacious proposal that radiolysis provides energy that splits water producing H₂O₂ which oxidizes pyrite (FeS₂) providing sulfate for the microbe. H₂ is also a byproduct for more reducing power! Mineral transformations in the environment are included in the cartoon, which I thought was a very nice touch that you don’t see in a biochemistry textbook. This microorganism might have been able to make a wide range of co-factors including cobalamin (for vitamin B12). It has a typical wide range of transporter proteins providing info on what might go in and out, and it has the usual carbon fixation pathways that I’m interested in.

 

It’s amazing that micro-organisms are found in tiny cracks of rock in the tens of nanometers wide. Very little water can penetrate in, yet somehow enough does for it to make a living in thin films of water just nanometers thick. I’m dumbfounded. Life does find a way to adapt, even in the freezing cold below the surface where stones are turned into bread. Could something be found on Mars? I don’t know. But it will be very expensive to find out and you’ll need quick-thinking knowledgeable Swiss-army-knife folks who know how to adapt.