In 1977, while Dr. Carl Woese and his colleagues at the University of Illinois were using a then new process
of DNA sequencing for studying relationships between bacteria, it was
discovered that there were two distinctly different groups. Those “bacteria”
that lived at high temperatures (extremophiles) or produced methane formed a
group quite different genetically from the usual bacteria. Because of this vast
genentic difference in makeup, Dr. Woese proposed that a new domain of life be
added…Archaea.
The scientific community was understandable shocked by this
proposal and for several years balked at accepting such a major revision in
century old thinking. Further research subsequently validated Dr. Woese’s
proposal and in 1990 the existing three domains of life (Bacteria, Archaea,
Prokaryote) were created.
Initially thought to exist only in extreme environments,
those devoid of oxygen and whose temperatures were near or above the boiling
point of water, microbiologists soon realized that Archaea are a large and
diverse group of organisms that are ubiquitous to all environments-terrestrial
and aquatic and significant contributors to the global carbon and nitrogen
cycles. It is the role of Archaea in the nitrogen cycle (specifically aquatic)
that is of interest and the focus of this document.
Since the acceptance of Archaea as a separate Domain of
life, research has been both intensive and massive, delving into all aspects of
this life form. Much of this research has been on the role of Archaea in the
Nitrogen Cycle with the results of this research simultaneously upending some
long held beliefs and yet clarifying other processes.
For Pondkeepers, maintaining the equilibrium of the Nitrogen
cycle is of the first order of importance. To be able to do so requires a
certain level of knowledge of how the involved biological processes work. Most
Pondkeepers know that Ammonia is oxidized by Nitrosomonas bacteria et.al. to
Nitrite which is oxidized by Nitrobacter bacteria et.al. to Nitrate which is
assimilated by algae and plants or reduced to Nitrogen gas by other bacteria.
Archaea do nothing to change this, but supplement the process, providing, shall
we say, more efficiency in the initial Ammonia oxidation stage.
AOA (Ammonia Oxidizing Archaea) and AOB (Ammonia Oxidizing
Bacteria) both occupy important niches in the Nitrogen cycle. In Oligotrophic
(low nutrient) waters, AOA are the predominant organisms and in Eutrophic (high
nutrient) waters AOB dominate.
In the world’s oceans, AOA are now known to be the primary
oxidizers of Ammonia, replacing AOB which for decades were believed to have
performed this function. The same has been found true in many freshwater lakes
and even in some soils. So what does this mean to a Pondkeeper?
Although no true research has been undertaken targeting
ponds specifically, there have been two (2) papers1,2 (2011 and
2014) addressing the roles of AOA and AOB in aquaria. Additionally, a Master’s thesis3 on this subject
was also written in 2014. The results of these three (3) documents can
logically be applied to garden ponds as both (ponds and aquaria) are closed
systems.
What was revealed in all of these research documents was
that in established and balanced aquaria, AOA were not only the
dominant, but in some cases, the only oxidizer present. This is not to imply
that AOB have lost their status as being an integral part of a pond’s Nitrogen
cycle, but that their role of importance is limited to establishing the initial
balance in a new pond when Ammonia levels are high.
This begs the question: Does this really change anything?
The simple answer is…No. It does, however, because of some
unusual characteristics of AOA, offer a different perspective on the Nitrogen
cycle process.
For instance, it has been shown that AOA are fully capable
of Ammonia oxidation in suboxic (low oxygen) conditions. They have been
isolated from the sludge at various Waste Water Treatment Plants which were
almost devoid of Oxygen. How Archaea are able to do this is still being
researched.
It has also been suggested by some, denied by others, that
AOA are still able to function at temperature approaching freezing. If proven
true it could make a difference to Pondkeepers in higher Latitudes.
As yet, Archaea have only been found that convert Ammonia.
None have been found that oxidize Nitrite. Considering the fact that research
into this amazing organism is really in its infancy, future surprising
discoveries can certainly not be ruled out.
For certain, with the newly acquired knowledge of AOA and
Anamox (a subject for another discussion), a new paradigm is required for the
Nitrogen Cycle.
References:
1. Temporal and Spatial Stability of Ammonia-Oxidizing
Archaea and Bacteria in Aquarium
Biofilters
Samik Bagchi1.¤,
Siegfried E. Vlaeminck1., Laura A. Sauder2,
Mariela Mosquera1,
Josh D. Neufeld2, Nico Boon1
2. Aquarium
nitrification revisited: thaumarchaeota are the dominant ammonia oxidizers in
freshwater aquarium biofilters
Laura A. Sauder,
Katja Engel, Jennifer C. Stearns¤, Andre P. Masella, Richard Pawliszyn, Josh D.
Neufeld
3. Ecology of Ammonia-oxidizing Archaea and Bacteria in
Freshwater Biofilters
Natasha
Alexandria Szabolcs
