Remember the sampling of a lake below the Antarctic ice sheet about a year ago?

They have found microbes living in the water, and the big way: 4,000 species observed in the small sample and 100,000 individuals per quarter teaspoon
http://www.latimes.com/science/sciencenow/la-sci-sn-microbe-ecosystem-antartic-ice-sheet-20140819-story.html

The microbes are said to feed on rock fine-ground by glacier movement, for which I'd like more details. Because, if they feed on still unoxidized metals, the same may happen on Europa (...see my script to put a probe there) and Enceladus, but if they chew organic matter produced earlier and elsewhere by an other life, the process doesn't suffice alone for life without sunlight.

 

Very nice findings!

The fines will contain very few metals, or metallic ores, but will be dominated by silicates, most of which will have weathered to phyllosilicates (i.e. clays). I'm not clear what reactions they would employ to extract energy from these.

It somewhat annoys me that in these kind of reports use "feeding" for respiration as well as nutrient acquisition. Obviously, neither metals nor silicates can provide biomass. Reduced metals could be electron donors, but the question would be what the acceptor would be (respiration). And pure silicates won't do at all.

Clays are enormously varied in their structure. Substitutions of aluminium for silicon and alkaline Earths for aluminium in the some of the silica tetrahedra and aluminium octahedra respectively create charge imbalances that lead to very interesting surface chemistry. I cannot specifically rule out, from my limited knowledge on the subject, a possible chemotrophic process. Do you have specific theory that would exclude that possibility?

Based on memory (though I could be wrong of course), in most cases the redoxpotentials would be incredibly tricky. Especially in the described scenario they would have to be electron donors but in the absence of oxygen there is little in terms of possible acceptors. Respiration-dependent accumulation was observed in some bacteria, but always in presence of oxygen. I believe there was also the possibility of iron silicates but the options are very limited.

That being said, my statement does appear to be rather absolute and I should have qualified it a bit more.

An option for "respiration" would be the reaction of (metallic) iron with sulphate.

Whenever that ice fell out of the sky, it would have picked up some SOx on the way down.