Nitrosomonas europaea, the model AOB, is an obligate chemolithoautotroph
deriving its energy for growth and activity from
the oxidation of NH3 to nitrite (NO
2 ). Utilizing a two-step process
in which the ammonia monooxygenase enzyme (AMO) oxidizes
NH3 to hydroxylamine (NH2OH) which is further oxidized to NO
2
via the hydroxylamine oxidoreductase enzyme (HAO), N. europaea
generates a net gain of 2 mol of electrons for every mol of NH3 oxidized
to NO
2 . These electrons are shuttled further down the electron
transport chain for cell growth and maintenance (Arp et al.,
2002). N