Effect of culture age on the kinetics of microcolony formation using a soil oligotrophic bacterium.

Abstract

The microcolony formation of a soil oligotrophic bacterium, S2336, isolated from a paddy soil was observed by using microculture chamber and phase-contrast optics. The kinetics of the microcolony formation was formulated by the following model: The microcolony number N t at time t is given by; N t = N∞[1−exp{−λ(t − t r )}] where N∞ is the expected number of microcolonies when time goes to infinity, λ is the rate of microcolony appearance per unit time, and t r is the retardation time. The model was, in form, the same as that of a first order chemical reaction and thus called the first order reaction (FOR) model. In the previous studies using Agromonas sp. and Escherichia coli, the t r values of the formation of microcolonies were the same whatever the culture age of parent cells was. In the present study, however, we observed another case in which the t r values of the bacterium, S2336, increased with the culture age of inoculum although the generation time was almost the same regardless of the age of the inoculum