Differences in the Characteristics of the Bacterial Community in the Epilithon and River Water as Demonstrated by Plate Counts Using Different Temperatures and Staining Methods.

Abstract

A study was made on seasonal fluctuations in bacterial density in the water column and the benthic epilithon at Koremasa, near the site of the most recent study of the River Tamagawa in Tokyo. Water quality and environmental factors at Koremasa were influenced largely by fluctuations in discharge at the site. Consequently, the amounts of DOC and P-compounds were correlated with the discharge summed for 5 days before the sampling day. Principal component analysis of water quality and environmental factors showed that the first principal component was composed of DOC, PO4-P, TDP, NH4-N, NO3-N and chlorophyll-a in the epilithon. The bacterial densities in the river water and epilithon were determined by the acridine orange direct count (AODC), INT-formazan count (INT) and agar plate method employing four different incubation temperatures. Changes in bacterial density estimated by plate counts at 20°C and 30°C in the epilithon were highly correlated with the first principal component. The percentage of the INT/AODC was higher in the epilithic microbial community than in the water one. However, bacterial density in the river water was controlled different factors investigated in this study. Thus, the bacteria on the upper surface of the benthic pebbles constitute an autochthonous community. Most of those in the water column may be allochthonous species flowing in the water.