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.