each other as well as all other archaea/bacteria through molecular signatures known as conserved signature indels. These studies have also identified 68 conserved signature proteins (CSPs) whose homologs are only found in the members of these three orders and 13 conserved signature indels (CSIs) in different proteins that are uniquely present in the members of the class Haloarchaea. These CSIs are present in the following proteins: DNA topoisomerase VI, nucleotide sugar dehydrogenase, ribosomal protein L10e, RecJ-like exonuclease, ribosomal protein S15, adenylosuccinate synthase, phosphopyruvate hydratase, RNA-associated protein, threonine synthase, aspartate aminotransferase, precorrin-8x methylmutase, protoporphyrin IX magnesium chelatase and geranylgeranylglyceryl phosphate synthase-like protein. Living environment Haloarchaea require salt concentrations in excess of 2 mol/L (or about 10%, three times the ocean salinity which is around 35g/L salt – 3.5%) in the to grow, and optimal growth usually occurs at much higher concentrations, typically 20–30% (3.4 - 5.2 mol/L of NaCl). However, Haloarchaea can grow up to saturation (about 37% salts). Optimal growth also occurs when pH is neutral or basic and temperatures at 45°C. Some haloarchaea though can grow even when temperatures exceed 50°C. Haloarchaea are found mainly in hypersaline lakes and solar salterns. Their high densities in the water often lead to pink or red colourations of the water (the cells possessing high levels of carotenoid pigments, presumably for UV protection). The pigmentation will become enhanced when oxygen levels are low due to an increase in a red pigmented ATP. Some of them live in underground rock salt deposits, including one from middle-late Eocene (38-41 million years ago). Some even older ones from more than 250 million years ago have been reported. Haloarchaea is also used to treat water that is high in salinity. This is due to its ability to withstand high nutrient levels and the heavy metals that may be present. Adaptations to environment Haloarchaea can grow at an aw close to 0.75, yet a water activity (aw) lower than 0.90 is inhibitory to most microbes. The number of solutes causes osmotic stress on microbes, which can cause cell lysis, unfolding of proteins and inactivation of enzymes when there is a large enough imbalance. Haloarchaea combat this by retaining compatible solutes such as potassium chloride (KCl) in their intracellular space to allow them to balance osmotic pressure. Retaining these salts is referred to as the “salt-in” method where the cell accumulates a high internal concentration of potassium. Because of