Ammonium removal characteristics of facultative heterotrophic nitrifying bacteria isolated from shortfin eel ( Anguilla bicolor) recirculation aquaculture system

Nitrifying bacteria play a role in reducing the amount of toxic ammonia in the rearing media. The purpose of this study was to characterize, and identify nitrifying bacteria isolated from shortfin eel (Anguilla bicolor) recirculation aquaculture system. The selective anorganic nitrifying medium was used to isolate the bacteria, followed by cultivation of the bacterium in the organic medium (Triptone Soya Agar). Bacterial characterization was carried out for nine days using a nitrification activity test. A safety test was conducted by intraperitoneal injection of bacteria in healthy eels (Anguilla bicolor). Phenotypic characterizations and analysis of the 16S rRNA and DNA gyrB genes were used to identify the bacteria. This study resulted in the successful isolation of five isolates. The three isolates (ENS2, ENS4, and ENS5) were non-pathogenic and exhibited high nitrifying activities. The isolates reduced 40-50 of ammonia concentration in three days, resulting in a 2-5 mg/L of nitrate concentration in the medium. The 16S rRNA and gyrase B genes sequences of ENS5 were close to Klebsiella quasipneumoniae, but with the low similarity (97.9 and 99.3, respectively). It is concluded that recirculation aquaculture system of shortfin eel (Anguilla bicolor) harbor of facultative heterotrophic nitrifying bacteria has potential for further application in shortfin eel aquaculture waste treatment facilities.