抄録
The survival of Escherichia coil K-12 and Pseudomonas putida BH inoculated into fresh water, sea water, activated sludge, and soil microcosms was studied. Three kinds of microcosms, named as intact, protozoa-free (filtered with 1.0μm filter or 2.0 g/l of cycloheximide added), and sterilized microcosms (filtered with 0.22μm filter or autoclaved twice at 120°C for 20 min.), were made from each kind of environmental sample, and used for the survival studies in order to separately evaluate the general effects of protozoan predation, interaction with indigenous bacteria, and starvation. In the all intact microcosms, both exogenous bacterial populations decreased rapidly by 1 to 4 orders of magnitude over 7 d. The experimental results indicated that the interaction with indigenous bacteria, especially in the form of antagonism or amensalism, was the most influential factor causing the decline of the exogenous bacterial populations, and that the protozoan predation was much less influential. To demonstrate evidence for the presence of such antagonism, heterotrophic bacteria indigenous to each intact microcosms were isolated, and their antagonistic activities against the introduced exogenous bacteria were examined. Approximately 1.0-3.5% of the isolated bacterial strains showed antagonistic activity against either E. coil K-12 or P. putida BH. However, the antagonistic activity exerted by most strains was found to be unstable.
