Differences in plating efficiency of bacteria from river epilithon sampled from upper and lower surfaces of artificial substrata.

The bacterial generic composition of biofilms was investigated by determining colony-forming units on 1/2 PYG (peptone, yeast extract, and glucose medium) agar plates. The biofilms developed on the upper and lower surfaces of artificial substrata submerged in river water at Unazawa in the Tamagawa River in Tokyo, Japan. Greater variation in the number and generic composition in platable colonies was obtained on the upper surface of an artificial substratum than on the lower surface. This variation corresponded to the variation in algal biomass. Accompanying the growth of the algae, specific bacteria commensal with the algae proliferated on the upper surface. The biofilm exfoliated when the surface density of chlorophyll was 11.2 μg·cm(-2). When the biofilm exfoliated, the bacterial community accompanying the algae also exfoliated, and the bacterial composition altered. The bacterial composition after exfoliation resembled that observed on the lower surface. The generic composition on the upper surface soon after it was initially submerged resembled that observed in the river water. The bacterial generic composition on the lower surface of the artificial substrata did not change greatly throughout the investigation because of the constant environmental conditions. The difference between the bacterial generic composition on the upper and lower surfaces was due to the fact that bacteria commensal with algae proliferated on the upper surface but not on the lower.