Details for Thermoplasmataceae

Thermoplasma is a chemoorganotroph and grows optimally at 55°C and pH 2 in complex media. Species of Thermoplasma are facultative aerobes, growing either aerobically or anaerobically by sulfur respiration. From a morphological point of view Thermoplasma resembles the mycoplasmas in that it lacks a cell wall. Most strains of Thermoplasma have been obtained from self-heating coal refuse piles. Coal refuse contains coal fragments, pyrite, and other organic materials extracted from coal, and when dumped into piles in coal-mining operations, tends to self-heat by spontaneous combustion. This sets the stage for growth of Thermoplasma, which apparently metabolizes organic compounds leached from the hot coal refuse. The species T. volcanium, has been isolated from solfatarra fields throughout the world and is highly motile by multiple flagella.

To survive the osmotic stresses of life without a cell wall and to withstand the dual environmental extremes of low pH and high temperature, Thermoplasma has evolved a cell membrane of chemically unique structure. The membrane contains a lipopolysaccharide-like material (referred to as lipoglycan in mycoplasmas) consiting of a tetraether lipid with mannose and glucose units. This molecule constitutes a major fraction of the total lipid composition of Thermoplasma. The membrane also contains glycoproteins but not sterols. Together these and other molecules render the Thermoplasma membrane stable to hot acid conditions.

The genome of Thermoplasma is of interest. Like other mycoplasmas, Thermoplasma contains a small genome (1.5mB). In addition, the DNA is complexed with a highly basic DNA binding protein that organizes the DNA into globular particles resembling the nucleosomes of eukaryotic cells. This protein is homologous to the basic histone proteins of eukaryotic cells. Similar DNA-binding histonelike proteins have been found in several hyperthermophilic Euryarchaeota.