Abstract
When bacteria of a paddy field soil were incubated on counting plates the number of colonies increased intermittently with broadening intervals. To analyze the bacterial populations, 30 to 51 bacteria were respectively isolated from the colonies appearing in each of the incubation periods: from 22 to 30h, 31 to 51h, 52 to 114h, and 115 to 265h. The isolates from each period were divided into groups I, II, III, and IV. The generation time of bacteria of each group, grown on the liquid medium of the same composition as used for counting, increased in order from group I to group IV. Frequency distribution of generation time in each group was of L-type. Morphological and physiological characteristics of the isolates differed among the types. The percentage of oligotrophic bacteria among isolates increased sharply from group I to group IV.
