Micrarchaeota

Micrarchaeota are a phylum of ultra-small archaea. This phylum was originally discovered via genomic investigation of acid drainage from a mine, and this species was referred to as ARMAN-2 in the literature. Micrarchaeota are a part of the DPANN super phylum and the kingdom Nanobdellati. The phylum is thought to contain at least 2 families and 12 genera.

This phylum is characterised by its incredibly small cell size and genome. A Micrarchaeum genome is roughly 1mbp long, and on average codes for 912 different genes. This phylum is anaerobic (or perhaps micro-aerobic, meaning that they can withstand micro quantities of oxygen) and appears to have co-evolved with Thermoplasmatales, due to Micrarchaeota often being in mutualistic relationships with Thermoplasmatales. Whilst many species of the Nanobdellati are host-dependent, and multiple species of Micrarchaeota such as ARMAN-2, and ca. M. harzensis are known to be host dependent, other species within Micrarchaeota such as Sv326 are thought to be free-living organisms. This illustrates the diversity of the phylum, and highlights the need to research this phylum further.