2007 Volume 16 Issue 4 Pages 305-312
Using an adhesion substrate (carrier of bacteria attached) and antagonistic bacteria of the Strain LMC9, this research produced a bioreactor and examined its repressing effect on the growth of the cold-water disease pathogen Flavobacterium psychrophilum on Ayu fish (Plecoglossus altivelis). Initially, a sterilized microscopic glass slide (2.6×7.6 cm) was adopted in order to check the interactions between the antagonistic bacteria LMC9 and F. psychrophilum on the adhesion substrate; that is, we followed fluctuations in the number of bacteria attached to it under different conditions. Consequently, when the glass slide was first immersed into antagonistic bacterium liquid, and successively immersed into the F. psychrophilum liquid (109 CFU (colonyforming unit) ml-1), the number of F. psychrophilum attached to the glass slide decreased with increasing concentrations of LMC9. The number of attached F. psychrophilum decreased significantly when the glass slide was immersed first in LMC 9 liquid of a concentration exceeding 107 CFU ml-1; the number of attached bacteria was several hundred times less than when immersed in 106 CFU ml-1 of LMC9 liquid.
Zeolite as an adhesion substrate was immersed in 106 CFU ml-1 of Strain LMC9 for 1h and then packed into a glass column to construct the bioreactor. When F. psychrophilum liquid (104 CFU ml-1) was introduced into this bioreactor at a rate of 1 L d-1, F. psychrophilum could not be detected in the outflow liquid even on the 14th day, using the agar plate culture method. But when F. psychrophilum at a concentration of 106 CFU ml-1 was introduced into the bioreactor, the above effect was not obtained; that is, F. psychrophilum in the outflow was detected on the agar medium by the 2nd day of the experiment.
The outflow liquid from the bioreactor was examined with a PCR device to clarify whether even a very low concentration of F. psychrophilum could be detected when 104 CFU ml-1 of F. psychrophilum was introduced into the bioreactor. As a result, DNA of F. psychrophilum was detected on the chromatogram after PCR. This suggests that the growth ability of F. psychrophilum was repressed due to the antagonistic bacterial effect in the bioreactor, and consequently F. psychrophilum could not form colonies on an agar plate medium.
