Evidence of Exponential Growth of an Anammox Population in an Anaerobic Batch Culture

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Twenty-five replicates of growth medium for anaerobic ammonium oxidation (anammox) containing ¹⁵N-labeled ammonium and non-labeled nitrite were inoculated into an anammox enrichment culture at low density, and anaerobically incubated batchwise. In the headspace, ²⁹N₂ partial pressure linearly increased via anammox in 25 vials, confirming that anammox populations were viable in all subcultures. On prolonged incubation, exponential increases in ²⁹N₂ were not observed in all but 13 subcultures, suggesting that the anammox population may not proliferate unless all conditions for growth are satisfied. The estimated first-order rate coefficients in those 13 subcultures varied from 0.0029 to 0.0048 h^-1.