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Once it becomes uncomfortable for microorganisms, e.g. due to lack of food, they form endospores in order to survive the unfavourable period of time. Endospores have a reduced metabolism and are resistant to external influences such as temperature, pH value and UV radiation. This resistance is guaranteed by various mechanisms: Endospores have a low water content, a number of protective layers and DNA-protecting proteins. Once the conditions have improved, endospores can return to a normal bacterial cell. Endospores are mainly formed by gram-positive bacteria.
Explanation for children:
When things get uncomfortable for microorganisms, e.g. when they are very hungry, they switch on an energy-saving mode - they form endospores. As such endospores, they can survive for a long time without having to eat. In addition, endospores can withstand UV radiation and hot temperatures, and almost nothing can destroy them. When there is enough food again, the endospores can develop into normal cells that are no longer in economy mode. Not all microorganisms can form endospores.