The kingdom Archaebacteria is biochemically different from Eubacteria. Most of these species can or have adapted to extreme enviroments such as extreme temperatures, or acidity of their enviroment. They only reproduce asexualy and there are only about 100 species.
Methanogens are non-oxygen consuming methane producers. Most of these bacteria use carbon dioxide as their carbon source. They are found in soil, swamps, most animals digestive tract. and the large human intestine. They usually produce about 2 billiion tons of methane gas annualy.
Thermoacidophiles are always found in hot enviroments, that are also highly acidic. There are also species that can tolerate temperatures up to 230°F. They also depend on sulfur and are mostly all anaerobes.
This type of bacteria lives in areas with very high salt content, such as the Dead Sea. They are mostly aerobic but some are anaerobic. They are all Gram-negative.
Pyrodictium occultum is commonly found in deep sea hydrothermal vents. It requires sulfur ro live. It can survive in extremely high tempatures and can withstand highly acidic envirments. It holds a tie with for bacteria that can withstand the hottest tempratures. It is also one of the most primitive types of bacteria in this class.