Summary
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.
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’.
15
N‐tracer experiments demonstrated that ‘
Ca
. B. sinica’ cells could reduce
to NH
2
OH, instead of NO, with as yet unidentified nitrite reductase(s). Furthermore, N
2
H
4
synthesis, downstream reaction of
reduction, was investigated using a purified ‘
Ca
. B. sinica' hydrazine synthase (Hzs) and intact cells. Both the ‘
Ca
. B. sinica’ Hzs and cells utilized NH
2
OH and
, but not NO and
, for N
2
H
4
synthesis and further oxidized N
2
H
4
to N
2
gas. Taken together, the metabolic pathway of ‘
Ca
. B. sinica’ is NH
2
OH‐dependent and different from the one of ‘
Ca
. K. stuttgartiensis’, indicating metabolic diversity of anammox bacteria.