Resistance of the Azotobacter cyst

Socolofsky, M. D. (University of Texas, Austin) and Orville Wyss. Resistance of the Azotobacter cyst. J. Bacteriol. 84:119-124. 1962-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.