Growth kinetics of Candidatus 'Methanoperedens nitroreducens' enriched in a laboratory reactor

Recently it has been shown that Candidatus 'Methanoperedens nitroreducens', an anaerobic methanotrophic archaea (ANME), can reduce nitrate to nitrite using electrons derived from anaerobic oxidation of methane. In this study, the growth kinetics of 'M. nitroreducens' enriched in a laboratory reactor were studied. In the experimental concentration range (up to 16 mg CH₄ L^-1), anaerobic oxidation of methane by 'M. nitroreducens' was found to comply with first order kinetic model with a rate constant of 0.019 ± 0.006 h^-1 and a biomass-specific rate constant of 0.04-0.14 L h^-1 g^-1VSS. Meanwhile, the nitrate reduction to nitrite was well described by the Monod-type kinetic model with an affinity constant for nitrate of 2.1 ± 0.4 mg N L^-1, which is slightly higher than, but comparable to, that of most known denitrifying bacteria. This is the first time that the growth kinetics of 'M. nitroreducens' have been experimentally studied. The applicability of the kinetic model reported herein to this organism or similar organisms in natural or engineering systems requires further investigation.