Eubacteria are true bacteria, a class of bacteria that includes organisms with non-branched cells and strong cell walls that have the form of small thin rods, less often cocci, among them are also filamentous and spiral forms. Some eubacteria form endogenous heat-resistant spores whereas most of them are non-spore-forming gram-negative forms. A rigid cell wall is a major adaptation in eubacteria. It allows survival in extreme conditions. As a result, some bacteria can survive in conditions characterized by high or low temperatures, high salt concentration, low or high pH, etc. The formation of spores is another adaptation to extreme conditions. In addition, various groups of eubacteria can metabolize different bioorganic compounds using them as a source of energy.