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

Twenty-five replicates of growth medium for anaerobic ammonium oxidation (anammox) containing (15)N-labeled ammonium and non-labeled nitrite were inoculated into an anammox enrichment culture at low density, and anaerobically incubated batchwise. In the headspace, (29)N(2) partial pressure linearly increased via anammox in 25 vials, confirming that anammox populations were viable in all subcultures. On prolonged incubation, exponential increases in (29)N(2) 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).