Although salts are required for all life from, halophiles are distinguished by their requirement of hypersaline conditions for growth. They may be classified according to their salt requirement; slight halophiles grow optimally at 0.2-0.85 mol L-1 (2-5%) NaCl; moderate halophiles grow optimally at 0.85-3.4 mol L-1 (20-30%) NaCl. In contrast, nonhalophiles grow optimally at less than 0.2 mol L-1 NaCl. Halotolerant organisms can grow both in high salinity and in the absence of a high concentration of salt. Many halophiles and halotolerant microoganisms can grow over the wide range of salt concentration with requirement or tolerance for salt some time depending on environmental and nutritional factors.