Isolation and Properties of a Deuterium-Tolerant Mutant of Pasteurella tularensis.

A spontaneously occurring stable deuterium-tolerant mutant was selected from highly virulent Pasteurella tularensis strain SCHU S4; the frequency of mutants in the cell populations was between 10(-3) and 10(-4). Upon cultivation of parent strain SCHU S4 in media containing D(2)O in lieu of H(2)O, inhibitory effects became manifest at 18% D(2)O and increased significantly beyond 54% D(2)O; mutant strain SCHU DT was not inhibited by media containing as much as 98% D(2)O. When cultivated in media containing D(2)O, mutant SCHU DT, in comparison with parent strain SCHU S4, showed a significant reduction in dermal and respiratory virulence for laboratory animals. Its immunogenic properties were comparable to viable P. tularensis vaccine strain LVS. Data on the comparative growth of various P. tularensis strains on media containing D(2)O suggested that "Old World" strains might be more tolerant to isotopic substitution of deuterium for protium than North American strains. Because of the residual virulence of SCHU DT for experimental animals it is believed to have limited value as a potential live vaccine strain.