Simultaneous Nitrite-Dependent Anaerobic Methane and Ammonium Oxidation Processes

<jats:title>ABSTRACT</jats:title> <jats:p> Nitrite-dependent anaerobic oxidation of methane (n-damo) and ammonium (anammox) are two recently discovered processes in the nitrogen cycle that are catalyzed by n-damo bacteria, including “ <jats:named-content content-type="genus-species">Candidatus</jats:named-content> Methylomirabilis oxyfera,” and anammox bacteria, respectively. The feasibility of coculturing anammox and n-damo bacteria is important for implementation in wastewater treatment systems that contain substantial amounts of both methane and ammonium. Here we tested this possible coexistence experimentally. To obtain such a coculture, ammonium was fed to a stable enrichment culture of n-damo bacteria that still contained some residual anammox bacteria. The ammonium supplied to the reactor was consumed rapidly and could be gradually increased from 1 to 20 mM/day. The enriched coculture was monitored by fluorescence <jats:italic>in situ</jats:italic> hybridization and 16S rRNA and <jats:italic>pmoA</jats:italic> gene clone libraries and activity measurements. After 161 days, a coculture with about equal amounts of n-damo and anammox bacteria was established that converted nitrite at a rate of 0.1 kg-N/m <jats:sup>3</jats:sup> /day (17.2 mmol day <jats:sup>−1</jats:sup> ). This indicated that the application of such a coculture for nitrogen removal may be feasible in the near future. </jats:p>