Diversity of Durable Dormant Cells: Insights into the Structure, Germination, and Resistance Mechanisms of Spores, and How to Analyze Damaged Spores

Five types of durable dormant cells in bacteria are known, and they do not have evolutionary connections to each other. The endospore of Bacillus and Clostridium, the exospore of Streptomyces, the myxospore of Gram-negative bacteria Myxococcus xanthus, the cysts of Gram-negative bacteria Azotobacter, and the akinetes of the cyanobacterium Anabaena cylindrica are known. Although they are molds rather than bacteria, the ascospores of Talaromyces, Neosartorya, and Byssochlamys show the same level of heat resistance as endospores of bacteria, and food contamination accidents have occurred. Endospores of Bacillus and Clostridium show significant resistance to elevated temperature, high pressure, ultraviolet light, radiation, and chemical agents and are often used as biological indicators (BI) in sterilization. Spore-forming bacteria are found in diverse environments, including natural settings and the food industry. Some of them can cause health issues in animals and humans. The aim of this paper is to offer an overview of the most recent discoveries and remaining questions concerning exosporium and spore coat structure, dehydration in the spore core, DNA protection, DNA repair systems, and germination mechanisms, particularly those associated with spore resistance, which have been thoroughly investigated. Additionally, it provides a summary of techniques for investigating damaged spores. This information will be valuable for understanding the mechanisms underlying physical or chemical disinfection methods and for selecting the most suitable culture medium for colony counting.