[Relationship between bacteria decomposing organic substances and water pollution in river water]

In order to clarify the relationship between water pollution and bacteria decomposing organic substances, 48 samples of river water were collected at twelve stations of the Chikuma-Sai river system. The bacteria decomposing organic substances were enumerated and identified by GM plates, which contained fewer organic substances than agar plates. Sixteen biological-physicochemical examinations of the river water were also performed. The results were as follows: temperature and dissolved oxygen in river water influenced the number of bacteria decomposing organic substances; proportions of bacteria decomposing degradable organic substances were higher in summer and spring than those in winter and autumn; the proportions of bacteria decomposing undegradable organic substances were higher in winter and autumn than those in other seasons. Organic substances were decomposed mainly by Aeromonas, a coliform group of facultatively anaerobic Gram-negative rods, and Pseudomonas, Gram-negative aerobic rods. Organic substances decomposed by facultatively anaerobic Gram-negative rods were much more degradable than those decomposed by Gram-negative aerobic rods. It seemed that the bacterial population of Aeromonas and the coliform group in river water increased with increases in the effluent of domestic and sewage abundant in degradable organic substances. Although Gram-positive rods were hardly isolated from river water, most of them decomposed undegradable organic substances. These results suggest that most bacteria decomposing organic substances are mainly distributed in river water and soil, and that modification of the river environment influences self-purification of rivers.