Sunday Extremophile Blogging: The ARMAN and Thermoplasmatales archaea

ARMAN archaea, orange circles, with an arcaheon of the thermoplasma order, below them. The small orange particles are viruses. Nobody knows what the needle-like things do. Credit: Luis R. Cronolli/LBNL via ScienceDaily 

The ARMAN archaeon is a mysterious one (mentioned in the previous instalment of Sunday extremophiles). For one thing, it is found only in highly acidic pools of an abandoned mine in Northern California (pH < 1.5 or so; the water there is more like concentrated sulphuric acid. Related organisms are found in other acidic pools, according to Wikipedia), and it has one of the smallest genomes of all free-living organisms (that is, not parasites). Indeed, it is so small that it seems to be at the size limit for metabolic, non-parasitic life (some viruses -no metabolism, so no "life" in a sense- are bigger), with a correspondingly tiny genome (1 million base pairs, compared to hundreds of billions for complex organisms) and few ribosomes. And yet of this small genome (1 million base pairs), about 45% seems to be genes that are not found anywhere else. ARMAN could thus be the "minimal" metabolic organism - with the smallest set of genes necessary for metabolism, though it apparently interacts in some unknown way with other acidophilic archaea, perhaps to get some extra nutrition (the thermoplasmatales, among which are found the most acidophilic organisms known, thriving in pH 0.06 environments). 

I find these weird niches - far removed from human possibility - really fascinating. Are there any limits to the environments in which life can thrive, ultimately? ARMAN lives in an environment extremely hostile to most forms of life - yet even there, it is not alone (in fact, it is possible that life started in similar environments, so perhaps ARMAN's lineage is very old). Endless forms most beautiful indeed.