Hydroxylamine-dependent anaerobic ammonium oxidation (anammox) by "Candidatus Brocadia sinica"

M. Oshiki, M. Ali, K. Shinyako-Hata, H. Satoh, S. Okabe
Environmental Microbiology, (2016)

Hydroxylamine-dependent anaerobic ammonium oxidation (anammox) by "Candidatus Brocadia sinica"


Anaerobic ammonium oxidation, Anammox bacteria


​Although metabolic pathways and associated enzymes of anaerobic ammonium oxidation (anammox) of 'Ca. Kuenenia stuttgartiensis' have been studied, those of other anammox bacteria are still poorly understood. NO2- reduction to NO is considered to be the first step in the anammox metabolism of 'Ca. K. stuttgartiensis', however, 'Ca. Brocadia' lacks the genes that encode canonical NO-forming nitrite reductases (NirS or NirK) in its genome, which is different from 'Ca. K. stuttgartiensis'. Here, we studied the anammox metabolism of 'Ca. Brocadia sinica'. 15N-tracer experiments demonstrated that 'Ca. B. sinica' cells could reduce NO2- to NH2OH, instead of NO, with as yet unidentified nitrite reductase(s). Furthermore, N2H4 synthesis, downstream reaction of NO2- reduction, was investigated using a purified 'Ca. B. sinica' hydrazine synthase (Hzs) and intact cells. Both the 'Ca. B. sinica' Hzs and cells utilized NH2OH and NH4+, but not NO and NH4+, for N2H4 synthesis and further oxidized N2H4 to N2 gas. Taken together, the metabolic pathway of 'Ca. B. sinica' is NH2OH-dependent and different from the one of 'Ca. K. stuttgartiensis', indicating metabolic diversity of anammox bacteria. 


DOI: 10.1111/1462-2920.13355


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