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.
Highlights
Aquaculture in mudflats along the coast contributes significantly to the world food supply
Six strains were isolated from the sediment samples of the fish ponds under aerobic conditions, and the four strains (Table 1; Figure 1) that could remove the nitrite-N were selected according to their bromothymol blue (BTB) plate's reaction
Denitrification by strain DF-1 reached the peaks at pH pH 9.0 (Figure 3); its nitrite-N degradation rate reached 96% at pH 3.0 and was maintained at 97-99% at pH 7.0-9.0, but reached only 23% at pH 5.0 and 41% at pH 11.0
Summary
Aquaculture in mudflats along the coast contributes significantly to the world food supply. This process could be of particular importance in countries with scarce arable land but high population, such as China. The combined water surface area for aquaculture in mudflats was estimated at 122,000 ha in Jiangsu Province, China (Blancheton, 2000; Adachi et al, 2002). Nitrite is an important component in the nitrogen cycle, but it has become a matter of great concern for intensive aquaculture industry in recent years. The nitrite in the water rapidly increased because the substantial amounts of uneaten feedstuff and aquatic animal excretion are gene-.
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