From John Postgate, Emeritus professor of microbiology, University of Sussex
Colin Barras’s article on the newly discovered eukaryota among the deep earth biota was fascinating (27 April, p 36). Presumably, they are dependant on local bacteria for nutrients.
Since the 1930s we have known about microbial life capable of independence from sunlight: the sulphate-reducing bacteria that accelerate anaerobic corrosion of iron and steel. They consume the hydrogen that protects metallic iron from rusting.
Wet iron is hardly a viable primary energy source to support an ecology evolving over millennia. But in that hot South African gold mine, the local sulphate-reducing bacteria are different because their hydrogen is formed by the radiolysis of water when thorium or uranium decays. Thus they would seem to be primary producers for an ecology based on a non-solar energy source, yet one that has the continuity necessary to underpin evolution.
If so, these findings, as you say, have valuable consequences for our speculations on the existence of extraterrestrial life.
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Lewes, East Sussex, UK
