thermoplasma acidophilum thermoplasma acidophilum thermoplasma acidophilum is an archaeon, the type species of its genus. t. acidophilum was originally isolated from a self-heating coal refuse pile, at ph 2 and 59 °c. its genome has been sequenced. thermoplasma acidophilum scientific classification domain: archaea kingdom: euryarchaeota phylum: euryarchaeota class: thermoplasmata order: thermoplasmatales family: thermoplasmataceae genus: thermoplasma species: thermoplasma acidophilumdarland et al. 1970 it is highly flagellated and grows optimally at 56 °c (133 °f) and ph 1.8. the size of a cell is about 1 μm. t. acidophilum lacks a cell wall and the cell membrane is exposed directly outside. t. acidophilum shows various cell shapes depending upon growth conditions and stages. the full genome of thermoplasma acidophilum has been sequenced. it is only 1565 kb in size.