The present study investigated the phylogenetic affiliation and physiological characteristics of bacteria responsible for anaerobic ammonium oxidization (anammox); these bacteria were enriched in an anammox reactor with a nitrogen removal rate of 26.0 kg N m −3 day −1 . The anammox bacteria were identified as representing ‘ Candidatus Brocadia sinica’ on the basis of phylogenetic analysis of rRNA operon sequences. Physiological characteristics examined were growth rate, kinetics of ammonium oxidation and nitrite reduction, temperature, pH and inhibition of anammox. The maximum specific growth rate (μ max ) was 0.0041 h −1 , corresponding to a doubling time of 7 days. The half-saturation constants ( K s ) for ammonium and nitrite of ‘ Ca. B. sinica’ were 28±4 and 86±4 µM, respectively, higher than those of ‘ Candidatus Brocadia anammoxidans’ and ‘ Candidatus Kuenenia stuttgartiensis’. The temperature and pH ranges of anammox activity were 25–45 °C and pH 6.5–8.8, respectively. Anammox activity was inhibited in the presence of nitrite (50 % inhibition at 16 mM), ethanol (91 % at 1 mM) and methanol (86 % at 1 mM). Anammox activities were 80 and 70 % of baseline in the presence of 20 mM phosphorus and 3 % salinity, respectively. The yield of biomass and dissolved organic carbon production in the culture supernatant were 0.062 and 0.005 mol C (mol <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:ali="http://www.niso.org/schemas/ali/1.0/" id="ieq1" overflow="scroll"><mml:mrow><mml:msubsup><mml:mtext>NH</mml:mtext><mml:mtext>4</mml:mtext><mml:mtext>+</mml:mtext></mml:msubsup></mml:mrow></mml:math> ) −1 , respectively. This study compared physiological differences between three anammox bacterial enrichment cultures to provide a better understanding of anammox niche specificity in natural and man-made ecosystems.

Physiological characteristics of the anaerobic ammonium-oxidizing bacterium ‘Candidatus Brocadia sinica’