Distribution of denitrifying bacteria and its controlling factors in freshwater environments.

Distribution of denitrifying bacteria and its controlling factors were investigated in freshwater environments. Denitrifying bacteria were counted by use of PY-Nitrate liquid medium and the most probable number method. The population (100-103 cells·ml-1) fluctuated more remarkably than that of aerobic heterotrophic bacteria in eutrophic pond and lakes. The ratio of the number of denitrifying bacteria to that of aerobic heterotrophic bacteria (D/Aeh) was between 0.0001 and 0.1 in those environments. In non-stratified eutrophic pond and lakes, the number of denitrifying bacteria tended to increase as the concentration of total nitrogen increased. In a stratified eutrophic lake, the D/Aeh ratio tended to increase as the concentration of dissolved oxygen decreased. Denitrifying bacteria in both water and attached substances in a polluted river tended to increase in number with the increase in BOD. The D/Aeh ratio in water and attached substances was higher than 0.01. Almost all denitrifying bacteria detected in the Himon-ya Pond, Lake Nakanuma and the River Tamagawa were gram-negative. Pseudomonas was the genus most frequently isolated from every type of water and attached substance.