Thermoplasmatales

Thermoplasmatales is an order of archaea within the phylum Euryarchaeota, and in some classifications it is placed in the class Thermoplasmata. It comprises several genera, including Thermoplasma, Ferroplasma, and Picrophilus. Members are typically thermoacidophiles that lack a rigid cell wall and therefore are pleomorphic, ranging from coccoid to irregular shapes. The absence of a complete cell wall is a defining feature that influences their environmental tolerance and morphology.

Habitat and ecology: They inhabit hot, acidic environments such as volcanic hot springs, coal refuse piles, and acid mine drainage. Ferroplasma species are frequently associated with iron-rich, sulfur- or metal-contaminated environments, where they contribute to iron and sulfur cycling under low pH conditions.

Physiology and metabolism: These organisms are typically chemoorganotrophs or chemolithotrophs and often rely on organic compounds or inorganic energy sources such as reduced iron or sulfur compounds. Growth commonly requires low pH and elevated temperature; exact ranges vary by species. Their membranes contain distinctive archaeal lipids, and their lack of a cell wall makes them particularly flexible in shape but sensitive to osmotic stress.

Representative members: Thermoplasma acidophilum, which thrives in warm, acidic environments; Picrophilus oshimae and P. torridus, among the most acidophilic archaea, capable of growth at extremely low pH; Ferroplasma acidiphilum and related species, notable for iron oxidation in acidic habitats.

Taxonomic notes: Thermoplasmatales has undergone reclassification as molecular data accumulated. It is placed in the class Thermoplasmata with varying placements in higher taxa depending on the taxonomic framework. Ongoing genomic studies continue to refine family-level relationships within the order.