Abstract
SUMMARY
Three varieties of resting stage, an exospore and two types of cyst, were formed by methane-utilizing bacteria. Exospores were budded off by two types of organism, both of which underwent a change in morphology prior to spore formation. Exospores possessed some properties in common with endospores: staining properties, some structural features, mode of germination, desiccation and heat resistance, but contained no detectable dipicolinic acid. Some organisms formed desiccation-resistant cysts similar in morphology, staining properties and fine structure to cysts formed by Azotobacter species. Other strains formed non-desiccation-resistant bodies considered to be similar to immature azotobacter-type cysts. A desiccation-resistant cyst formed by one strain differed in structure and appearance from Azotobacter-type cysts and was referred to as a ‘lipid’ cyst.