Abstract

The aims of this study were to help the development of the models describing denitrification in the recirculation aquaculture systems and to contribute to the knowledge on the role of heterotrophic bacteria in aquaculture nutrient removal systems in mudflats along the coast. Six aerobic denitrifying strains were isolated by bromothymol blue (BTB) plate technique from the fish farm sediments in mudflat along the coast. The strain DF-1 was selected for the aerobic denitrification studies as it was highly effective in removing nitrite compared with other strains; it lowered the nitrite nitrogen (nitrite-N) concentration from 10 mg/L to zero in 20 h. The aerobic denitrification by the strain DF-1 occurred at significantly higher rates of nitrite-N degradation than the positive controls (sterile screening media) under different pH, temperature, and various concentrations of nitrite and salinity. The rate of nitrite-N degradation was 99.3, 97.7, 99.5, 96.5, and 91.8% when sucrose, glucose, sodium acetate, sodium succinate and potassium sodium tartrate, respectively, were used as the carbon source. The strain DF-1 contained the nirK gene as indicated by the amplification of nitrite reductase. The strain DF-1 was identified asKlebsiella oxytoca by the morphological observation and 16SrRNA gene analysis.

Key words: Coastal pollution, high nitrogen risk, aerobic denitrification, Klebsiella oxytoca, nitrite nitrogen degradation rate, aquaculture.