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Appl Environ Microbiol. 1974 July; 28(1): 41-46
Copyright © 1974 American Society for Microbiology. All Rights Reserved.

Increased Radiation Resistance of Vegetative Bacillus pumilus¹

Research Division, Ethicon, Inc., Somerville, New Jersey 08876, and Department of Biochemistry and Microbiology, Cook College, Rutgers University, New Brunswick, New Jersey 08903

ABSTRACT

A 4.5-fold increase in vegetative cell radiation resistance of Bacillus pumilus E601, the internationally recognized biological standard for irradiation sterilization, was obtained by the repeated passage of resistant survivors through successive sublethal doses of ⁶⁰Co irradiation. This increase in resistance was accompanied by a corresponding increase in spore resistance through the seventh irradiation passage. By the fifteenth passage, the ability for spore formation was lost. Other effects noted by the successive irradiation dosages included loss of motility and pellicle formation, and changes in the Gram reaction, cell morphology, and colonial morphology. Increased resistance was also accompanied by an increased nutritional requirement for specific amino acids. Radiation resistance was not transferred from vegetative cells to spores.

¹ A paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers University, New Brunswick, N.J. 08903