Abstract

Anaerobic ammonium oxidizing (anammox) bacteria are detected in many natural ecosystems and wastewater treatment plants worldwide. This study describes the enrichment of anammox bacteria in the presence of acetate. The results obtained extend the concept that the anammox bacteria can be enriched to high densities in the presence of substrates for heterotrophic growth. Batch experiments showed that among the tested biomass, the biomass from the Candidatus 'Brocadia fulgida' enrichment culture oxidizes acetate at the highest rate. Continuous cultivation experiments showed that in the presence of acetate, ammonium, nitrite and nitrate, Candidatus 'Brocadia fulgida' out-competed other anammox bacteria. The results indicated that Candidatus 'Brocadia fulgida' did not incorporate acetate directly into their biomass. Candidatus 'Brocadia fulgida' exhibited the common characteristics of anammox bacteria: the presence of an anammoxosome and ladderane lipids and the production of hydrazine in the presence of hydroxylamine. Interestingly, the biofilm aggregates of this species showed strong autofluorescence. It is the only known anammox species exhibiting this feature. The autofluorescent extracellular polymeric substance had two excitation (352 and 442 nm) and two emission (464 and 521 nm) maxima.