Until now, anaerobic ammonium oxidation
(anammox) has been widely applied as an alternative
method to the conventional nitrification–denitrification
pathway for biological nitrogen removal from wastewater.
Since their discovery in a denitrifying fluidized bed reactor
in the Netherlands in the early 1990s, anammox bacteria
have also been detected in natural environments. Anammox
is one of the newly found drivers known to contribute
to the biogeochemical nitrogen cycle. In the marine environment,
more than 50% of nitrogenous compounds are
reportedly converted into nitrogen gas via the anammox
pathway. These observations were made using state-of-theart
techniques for detecting anammox bacteria based on
their lipids, small-subunit ribosomal RNA genes, functional
genes, and unique reaction pathways. The research
objectives for anammox bacteria are quite diverse, ranging
from the application of anammox processes to various
wastewater types, to anammox biochemistry and phylogeny,
to elucidating how anammox bacteria have evolved.
Since the genome of the anammox bacterium Kuenenia
stuttgaritiensis was deciphered, anammox bacteria have
proved to be quite versatile. The next challenge is to enrich
knowledge of anammox bacterial physiology and phylogeny
to improve their use in engineered and natural environmental
systems and minimize nitrogen loads to
downstream water bodies. Furthermore, rapid startup of the
anammox process for engineered systems is required to
broadly harness the benefits of anammox bacteria. This
review article summarizes the physiology and phylogeny