Abstract

Aerobic denitrifying characteristics of duckweed rhizosphere bacterium RWX31 was studied in this paper. Bacterium RWX31 exhibited efficient growth stability and nitrogen removal ability, with nitrate removal efficiency of 81.3% at an initial 140 mg l^-1 NO₃-N. Under aerobic conditions, the maximum nitrate-N removal rates were 30.9, 24.3 and 11.5 mg l^-1 h^-1, with nitrate, nitrite and ammonium as sole nitrogen source, respectively. The optimal conditions for aerobic denitrification were C : N ratio of 8, pH 7.2 and 27°C when nitrate served as the substrate, and shaking speed had no significant impact on nitrate removal efficiency within the range tested (dissolved oxygen concentration 3.5 to 7.3 mg l^-1). Stationary test suggested that the association of duckweed and strain RWX31 performed better in nitrate-removal than by itself or in association with other bacteria species. According to the morphological observation and 16S rRNA gene analysis, strain RWX31 was preliminarily identified as Pseudomonas sp. Strain RWX31 is the first aerobic denitrifier isolated from duckweed Lemna minor rhizosphere with the potential to reduce nitrate leaching.

Key words: Aerobic denitrification, nitrogen removal, Pseudomonas, rhizobacteria