Takayuki Nishio

Conditions for nitrification and denitrification by an immobilized heterotrophic nitrifying bacterium Alcaligenes faecalis OKK17

Conditions to improve the efficiency of nitrogen removal were examined with the heterotrophic nitrifying/denitrifying bacterium Alcaligenes faecalis OKK17. This bacterium nitrifies ammonium and glutamate mainly to hydroxylamine and to a lesser extent to nitrite and nitrate, but it does not denitrify aerobically. Thus, the bacterium was immobilized in polyvinyl alcohol (PVA) hydrogel to provide anaerobic conditions in the gel support. Production of nitrous oxide in an oxygen-purged vial indicates that the nitrification products formed in the surface layer were denitrified in the subsurface layer of the gel. The specific total nitrogen removal activity by the immobilized cells in continuous flow culture was higher than the specific nitrification activity by a cell suspension. A possible explanation of this acceleration of nitrification is that it is due to reduction of deleterious nitrification products, i.e., hydroxylamine and nitrite at mM concentrations, by subsequent denitrification.

Isolation of aryl-phosphate ester-degrading bacterium from leachate of a sea-based waste disposal site.

An aryl-phosphate ester (APE)-degrading bacterium was isolated from the leachate of a sea-based waste disposal site. The isolated APE-degrading bacterial strain YS-57 grew well in a medium containing glucose and NaCl, and degraded two types of APE:tricresyl phosphate and triphenyl phosphate. The optimal temperature, pH, and NaCl concentration for the growth of strain YS-57 were 30 degrees C, 7.0, and 1.0%, respectively. Strain YS-57 grew at an APE concentration of 25 mg/l without being inhibited. APEs were degraded by the supernatant of the medium in which strain YS-57 was cultured, suggesting that the APE-degrading enzyme was released into the extracellular space in the logarithmic growth phase. The 16S rDNA sequence of strain YS-57 showed 95.6% similarity to that of Roseobacter gallaeciensis and the morphological properties were also comparable. Consequently, strain YS-57 was closely related to the genus Roseobacter.