exospore

An exospore is a tough, resistant outer layer found in some bacterial endospores, particularly those of the genus Bacillus. It is not a part of the endospore itself but rather an additional protective coat that is synthesized and deposited outside the spore coat layers. The exospore is primarily composed of proteins, and its exact composition can vary between species.

The formation of the exospore occurs during the final stages of sporulation, after the endospore has been fully assembled. It is secreted from the mother cell and envelops the mature endospore. This outermost layer is thought to provide enhanced resistance to various environmental stresses, including desiccation, heat, radiation, and chemical disinfectants. The exospore's specific contribution to overall resistance is a subject of ongoing research, but it is believed to act as a physical barrier.

Not all bacterial endospores possess an exospore. Its presence is a characteristic feature that has been observed in certain Bacillus species, such as Bacillus subtilis. The exospore's tough and durable nature can contribute to the long-term survival of these bacteria in harsh conditions, allowing them to persist in the environment for extended periods. Understanding the structure and function of the exospore is important for fields such as microbiology, astrobiology, and the development of sterilization techniques.