In an earlier posted article, Archaea The not-so-new-kids-on-the-block,
we briefly discussed the emergence of certain species of the Domain
Archaea as the prime ammonia oxidizing organisms in both terrestrial and
aquatic environments world-wide.
Over the past several years there has been increasing evidence that a
similar altering of perceived role dominance is extant in Nitrite
oxidation.
Some bacterial and archaeal species defy replication under lab condition
and have also defied easy identification by past known means. The
bacterium Nitrospira is one such micro-organism. Only recently has a
method been developed allowing for somewhat better identification. As a
result, what has been discovered has changed the paradigm not only as
relates to Nitrite oxidation but also, to a point, Ammonia oxidation.
Enough evidence has been amassed to date to confirm that in many aquatic
environments Nitrospira is the dominant Nitrite oxidizing specie
instead of Nitrobacter. This is most noticeable in waters that have an
elevated Ammonia level. These elevated Ammonia levels inhibit the
Nitrite oxidizing process in Nitrobacter but has no effect on the
efficiency of Nitrospira. This means in an aquatic habitat where the
Nitrogen cycle is not established or balanced Nitrospira will likely be
the dominant Nitrite oxidizer with Nitrobacter increasing in numbers
only when Ammonia levels have been reduced. This does not mean that
Nitrospira’s role becomes diminished. Nitrospira has the almost unique
ability to also convert Urea into Ammonia. It forms a quasi-symbiotic
relationship with Nitrosomonas and, it is suspected, Archaea, supplying
Ammonia in ezchange for Nitrite. So even in an established well-balanced
aquatic habitat the Nitrite oxidizing duties are at least shared by
Nitrobacter and Nitrospira.
In addition, Nitrospira remain active in anoxic conditions.
No longer are certain processes relegated exclusively to certain
micro-organisms, but rather new organisms have emerged as the dominant
players that are capable of performing multiple processes in the
Nitrogen cycle.
The paradigm continues to shift.
