Multiplication of Pseudomonas solanacearum in pure water.

Washed cells of the virulent isolates and avirulent or weakly-virulent mutants of Pseudomonas solanacearum suspended in pure water at a concentration of 102-3 cells/ml rapidly multiplied up to a level of 106 cells/ml during four days of incubation at 22C. The mode of multiplication was investigated with two virulent isolates, Ku7501-1 and KT-2, and avirulent mutant Ku7501-1-Av. All isolates multiplied to converge to the concentration of 106-7 cells/ml when initial concentration was low (less than 104 cells/ml) or moderate (104-6 cells/ml), while neither multiplication nor reduction occurred when initial concentration was high (higher than 106 cells/ml). The final concentration of the bacteria was maintained for long period. Bacterial multiplication in pure water was further confirmed by serial subculture experiment with the isolate Ku7501-1. When bacterial suspension was added to sterile pure water at a concentration of 102-3 cells/ml and subcultured serially 5 times, the bacteria multiplied up to 106-7 cells/ml during each incubation period of 3 days, suggesting that the cells propagated 1015 times in total. No difference was observed in the size of bacterial cells before and after multiplication with the electron microscope.