Enrichment and physiological characterization of an anaerobic ammonium-oxidizing bacterium ‘ Candidatus Brocadia sapporoensis’

Anaerobic ammonium-oxidation (anammox) is recognized as an important microbial process in the global nitrogen cycle and wastewater treatment. In this study, we successfully enriched a novel anammox bacterium affiliated with the genus ‘Candidatus Brocadia’ with high purity (>90%) in a membrane bioreactor (MBR). The enriched bacterium was distantly related to the hitherto characterized ‘Ca. Brocadia fulgida’ and ‘Ca. Brocadia sinica’ with 96% and 93% of 16S ribosomal RNA gene sequence identity, respectively. The bacterium exhibited the common structural features of anammox bacteria and the production of hydrazine in the presence of hydroxylamine under anoxic conditions. The temperature range of anammox activity was 20 − 45°C with a maximum activity at 37°C. The maximum specific growth rate (μmax) was determined to be 0.0082h−1 at 37°C, corresponding to a doubling time of 3.5 days. The half-saturation constant (KS) for nitrite was 5±2.5μM. The anammox activity was inhibited by nitrite with 11.6mM representing the 50% inhibitory concentration (IC50) but no significant inhibition was observed in the presence of formate and acetate. The major respiratory quinone was identified to be menaquinone-7 (MK-7). Comparative genome analysis revealed that the anammox bacterium enriched in present study shared nearly half of genes with ‘Ca. Brocadia sinica’ and ‘Ca. Brocadia fulgida’. The bacterium enriched in this study showed all known physiological characteristics of anammox bacteria and can be distinguished from the close relatives by its rRNA gene sequences. Therefore, we proposed the name ‘Ca. Brocadia sapporoensis’ sp. nov.