Thermoplasms

Thermoacidophiles are the characteristics of lacking cell walls. At present, only two genera, Thermoplasma and Picrophilus, are known. Thermoplasma grows in refuse piles of coal mines. These piles contain large amounts of iron pyrite (FeS), which is oxidized to sulfuric acid by chemolithotrophic bacteria. As a result the piles become very hot and acidic. This is an ideal habitat for Thermoplasma since it grows best at 55 to 59°C and pH 1 to 2.

Picrophilus is grows at sulfur fields with optimum pH requirement of less than 1. They are aerobic, irregular shaped cocci, having sulfur layer outside its plasma membrane.  

Extremely Thermophilic S-Metabolizers

This physiological group contains the class Thermococci, with one order, Thermococcales. The Thermococcales are strictly anaerobic and can reduce sulfur to sulfide. They are motile by flagella and have optimum growth temperatures around 88 to 100°C. The order contains one family and two genera, Thermococcus and Pyrococcus.

Sulfate-Reducing Archaea

Archaeal sulfate reducers are found in the class Archaeoglob i and the order Archaeoglobales. This order has only one family and one genus. Archaeoglobus contains gram-negative, irregular coccoid cells with walls consisting of glycoprotein subunits Archaeoglobus is extremely thermophilic.

2. Phylum- Crenarchaeota

They are the extreme hyperthermophiles which needs optimum temperature of 105°C for their growth.At present, the phylum contains 69 genera; two of the better-studied genera are Thermoproteus and Sulfolobus. Thermoproteus is a strict anaerobe and grows at temperatures from 70 to 97°C and pH values between 2.5 and 6.5. It is found in hot springs and other hot aquatic habitats rich in sulfur. Sulfolobus are aerobic, with a temperature optimum around 70 to 80°C and a pH optimum of 2 to 3.