RESISTANCE OF THE AZOTOBACTER CYST

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Abstract
The Azotobacter cysts were found to be more resistant than the vegetative cells to various harmful agents. Studies involving ultraviolet irradiation indicated that cysts required twice as great a dosage as correspondingly treated vegetative cells to be 90% inactivated. The acquisition of ultraviolet resistance during the encystment process was gradual and appeared to be related to the formation of exine and intine. A slow loss of ultraviolet resistance during germination was also noted. The cysts exhibited no marked resistance to heat; although they were extremely resistant to gamma radiation, sonic treatment and desiccation. Evidence was presented indicating that the cyst is not a bacterial endospore. The encystment process may confer a survival advantage upon the organism by coupling the low endogenous respiration rate with the ability to withstand desiccation.
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