Enrichment of an anammox bacterial community from a flooded paddy soil

This study describes the enrichment of anammox bacteria in a column simulating oxygen limited flooded paddy soils, which are important man-made ecosystems that receive substantial amounts of fixed nitrogen. The upper 50cm of the paddy soil, containing a high amount of ammonium [1.610.4mmolNkg(dry weight)1], was selected as the inoculum for anammox enrichment. After 18 months of incubation with freshwater from the paddy soil ecosystem, the enrichment culture consumed approximately 4mmolammoniuml1day1 and 5mmolnitritel1day1. The maximum specific anammox activity of the culture was 35.7molNg(dry weight)1h1. Fluorescence in situ hybridization indicated that anammox cells constituted 50%+/- 10% of the enrichment culture. The phylogenetic analyses of 16S rRNA and the diagnostic hydrazine synthase (hzsA) genes showed that two dominant anammox species were enriched from paddy soil. The enriched CandidatusAnammoxoglobus-like organisms showed a 16S rRNA gene similarity of 97.599.2% to CandidatusAnammoxoglobus propionicus and the CandidatusJettenia-like organisms showed 92.193.1% 16S rRNA gene identity to CandidatusJettenia asiatica. Real-time quantitative PCR of hzsA gene suggested that up to 1010copiesg(dry weight)1 of soil anammox bacteria were present in the enrichment culture.