Enrichment and physiological characterization of an anaerobic ammonium-oxidizing bacterium 'Candidatus Brocadia sapporoensis'.

We successfully enriched a novel anaerobic ammonium-oxidizing (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 produced 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 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 (IC50 =11.6mM) but not by formate and acetate. The major respiratory quinone was identified to be menaquinone-7 (MK-7). The enriched anammox bacterium shared nearly half of genes with 'Ca. Brocadia sinica' and 'Ca. Brocadia fulgida'. The enriched bacterium showed all known physiological characteristics of anammox bacteria and can be distinguished from the close relatives by its 16S rRNA gene sequence. Therefore, we proposed the name 'Ca. Brocadia sapporoensis' sp. nov.