High Quality Content by WIKIPEDIA articles! An endospore is a dormant, tough, and non- reproductive structure produced by certain Gram- positive bacteria from the Firmicute phylum that forms when a bacterium produces a thick internal wall that encloses its DNA and part of its cytoplasm. Examples include, but are not limited to, Bacillus and Clostridium. The primary function of most endospores is to ensure the survival of a bacterium through periods of environmental stress. They are therefore resistant to ultraviolet and gamma radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants. Endospores are commonly found in soil and water, where they may survive for long periods of time. Some bacteria produce exospores or cysts instead.