Physiological and taxonomical characteristics of the bacteria in water bodies containing organic matter in different concentrations were compared. It was found that (1) the population density of heterotrophic bacteria increased up to a certain limit in parallel with the concentration of organic matter in water, (2) the higher the concentration of organic matter in the water body, the higher the Cm value (the concentration of peptone in the counting medium which gives the maximum colony number); (3) the dominant group of bacteria was Flavobacterium in all the water bodies examined, and (4) there was a certain correlation between physiological characteristics of the dominant group of bacteria and the concentration of organic matter in the water body.

The relations between growth rate (ƒÊ, h-1) and organic nutrient concentrations (S,mg/l were examined by using natural bacterial populations and isolated strains in Lake Biwa. The kinetic Hiruta, Tamaki-cho, Watarai-gun,