2-35 Some microbes make other types of spores

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• Less resistant resting structures (spores and cysts) are formed by other microbial species.
• Spores and cysts are less resistant to harsh treatments than are endospores, but do have some resistance especially to desiccation.

Endospores are not the only type of spore made by microorganisms. Azotobacter species and several others are know to form cysts, which are dormant cells with thickened cells walls. Cysts are resistant to desiccation and some chemicals, but cannot withstand high temperatures as endospores can. The actinomycetes are a large group of spore-forming, gram-positive bacteria that grow by forming long tubules called filaments. Under nutrient poor conditions these filaments differentiate into round resting structures termed spores. In contrast to endospores, these structures are part of the reproductive process. The developmental process to create an actinomycete spore is less complex than that of the endospore. It involves the simple formation of cross walls that divide the filament into sections, each containing a chromosome. These then differentiate into mature spores. During this process a tougher cell wall is laid down and there is conversion of the cytoplasm to a dormant state so that the spore becomes more resistant to heat and chemicals, though not as hardy as an endospore. Actinomycete spores are capable of surviving for long periods of time (for years) and can germinate into vegetative cells when appropriate growth conditions are present. Many different genera are capable of forming this type of spore and the ability to form these structures does not seem to correlate with any group of microorganisms.

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