Abstract
To clarify the biodegradation of urea in river water, the concentration of urea and the cell number of heterotrophic urea-decomposing and urease active bacteria were examined in three rivers (six sites) located in north Kyushu. There were more urea-decomposing bacteria in the pollutted site (BOD 7.4mg·l-1, urea 0.114mg·l-1), 17±30×102 cells·ml-1, than in the relatively unpolluted site (BOD 1.0mg·l-1, urea 0.039mg·l-1), 1.4±1.8×102 cells·ml-1. The ratio of the average number of urea-decomposing bacteria to heterotrophic bacteria grown on PYG agar medium was 0.28%. However, 55 (30.5%) of 180 strains isolated from river waters contained urease activity.
In biodegradation experiments, urea added to river water at the concentration of 0.2-5mg·l-1 was not appreciably degraded. The results suggest that, in the river water of below 5 mg·l-1 of urea, most of the heterotrophic bacteria having urease are not transformed into the urea degrading or assimilating bacteria.
