Characterization of a novel heterotrophic nitrifying and aerobically denitrifying bacterium, Halomonas sp. Z8, as a potential bioagent for wastewater treatment

Aim: The aim of the present study was to identify and characterize the functions of key microbes mediating nitrification. Methodology : After sampling the biofilm from a submerged biofilter in a marine aquaculture system, selective media were used to isolate microbial strains involved in nitrification. Isolates were identified using physiological and biochemical assays and sequencing of 16S rRNA gene. Nitrogen removal under different conditions was characterized. Nitrogen removal pathway was characterized by a N-15 tracer experiment. Representation of key microbes in the biolfim was characterized by metagenomics analysis. Results : Single-factor tests showed that Halomonas sp. strain Z8 exhibited good heterotrophic nitrification and aerobic denitrification abilities, with maximum NH4+-N, NO2--N and No-3(-)-N removal rates of 2.37, 1.26 and 1.7 mg N l(-1) hr(-1), respectively. The N-15 isotope tracer experiment confirmed the aerobic nitrogen removal pathway of strain Z8. Average NO, removal efficiencies were all above 80% in an aerated moving bed bioreactor inoculated with strain Z8 and employed to treat synthetic marine aquaculture wastewater. Metagenomic microbial community analysis revealed that Halomonas sp. Z8 was one of the dominant taxa at genus level, suggesting a vital role in removing nitrate from bioreactor. Interpretation : The results of the present study indicate the potential of Halomonas sp. ZB for treating wastewater in marine re-circulating aquaculture systems.