New bacteria show ‘wonder upon wonder’
by David Demick
A recently discovered new type of bacteria is raising eyebrows among microbiologists,
organic chemists and environmental scientists. Their unique properties are creating
research challenges in nitrogen chemistry and membrane structure. They efficiently
perform a chemical operation that was thought to be impossible—conversion
of ammonia to pure nitrogen in the absence of oxygen (see figures 1 and 2). These
bacteria are named after their distinctive metabolism as ‘anammox’,
which is short for ‘anaerobic ammonia oxidation’. It is being suggested
that they show how life evolved in the early earth by providing a link between prokaryotes
and eukaryotes. However, on closer inspection, their unique features make them fit
in better with a creationist view of the microbial world.
Figure 1. Anaerobic ammonium oxidation (anammox) carried out by
anammox bacteria, where ammonium and nitrite are converted into dinitrogen gas.
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here for larger view
Waste tanks and deep waters
The story of their discovery begins with different but related observations. In
two very different environments (deep anoxic areas in natural water bodies, and
sealed oxygen-free organic waste tanks), ammonia content was noticed to be less
than expected. In addition, the waste tanks also showed production of nitrogen gas.
This anaerobic ammonia consumption coupled with nitrogen production was suspected
to the work of bacteria, but the chemical reactions involved were unknown in nature.
There was considerable skepticism until a Dutch microbiologist, Gijs Kuenen, succeeded
in isolating the responsible organism from the waste tanks. It was verified that
the new bacteria perform the hypothesized anammox reaction, converting ammonia and
nitrite to nitrogen and water under anaerobic conditions. However, this was only
the beginning of surprises to come from these newly recognized organisms.
A rocket-science puzzle
The new bacteria were provisionally named Brocadia anammoxidans, after
their bright red colour and distinctive chemistry. Electron microscopy revealed
something else unexpected—unlike most other bacteria, these had an internal
membrane-bound organelle. Furthermore, this organelle was unique. It appeared to
be crucial for the nitrogen-metabolizing process, and was accordingly named an ‘anammoxosome’.
For still another surprise, it was found to contain hydrazine, a highly toxic and
explosive nitrogen compound used in rocket fuel. Hydrazine’s hydrophobic structure
is such that it should diffuse easily through most biological membranes, and hence
it should kill the surrounding bacterium. How could these little organisms contain
and store such a dangerous substance?
Figure 2. The stoichiometry (quantities of reactants and products)
of anammox (from Strous et al).5
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here for larger view
A new molecule that looks like a ladder
The answer was found to lie in a novel organelle membrane structure, which provoked
such praise from organic chemists as ‘extraordinary’ and even ‘impossible’.
The membrane turned out to owe its remarkable impermeability to a tight, ladder-like,
carbon-rich, multi-ring structure made of linked cyclobutanes, and descriptively
termed ‘ladderane’ (see figure 3). It is still not clear just how the
microbes make this remarkable and unique membrane material, or why they use it to
contain hydrazine. It is thought that the hydrazine may function as a nitrogen-containing
intermediate form, and that its high energy content may drive the necessary nitrogen-forming
reactions. It is clear that the anammox bacteria will keep researchers busy for
some time to come. In the meantime, a synthetic process for making ladderane has
been patented, and it is hoped to eventually have applications in the electronics
field.1
Evolutionary headache
What of the origin of these strange organisms? The anammox bacteria have been classified
with the bacterial phylum Planctomycetes. This is a recently recognized group of
bacteria which have internal membrane structure, unlike most prokaryotes. Some have
an internal membrane that surrounds the genome, termed a ‘nuclear body’
or ‘nucleoid’. Other internal structures, such as the anammoxosome,
seem to be ‘primitive’ organelles. This gives them features similar
to eukaryotes (although the nucleoid is not a true nucleus). They also have a protein-rich
cell membrane that is free of peptidoglycan, a feature which they share with the
Archaea (a different group of bacteria-like organisms). On the other hand, their
genome structure is closest to the true bacteria, so they have some features in
common with three great domains of living things. Hence, evolutionists hope that
some of the Planctomycetes, including their newest anammox members, will qualify
as links between hypothetical earliest forms of life and subsequent diversifying
organisms.
However, attempts to fit these novel prokaryotes into an evolutionary scheme are
proving elusive.
However, attempts to fit these novel prokaryotes into an evolutionary scheme are
proving elusive.2 Similarities
are overshadowed by complex and crucial differences. For example, the anammoxosome
is completely unique, both in membrane structure and metabolic chemistry. It can’t
be called a stepping stone toward or from other organelles. The anammox microbes
fit better into a creationist view of bacteria, in which these tiny creatures are
a multitude of distinct and unique organisms, without evolutionary relationships,
created to reproduce after their own kind. Their God-given purpose is to maintain
a chemically livable biosphere—specifically, in this case, to help regulate
nitrogen balance and availability.
Figure 3. Ladderanes X and Y found in anammox lipids (above), and
an example of the chemical structure of ladderane Y (below).
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here for larger view
‘Millions of years’—or a superintelligent creator?
Origins questions aside, scientists are scrambling to exploit these bacteria in
sewage-treatment facilities and similar sites for detoxifying ammonia-rich waste,
where they are expected to greatly improve efficiency and lower toxicity. They are
also being found to be much more widespread in the biosphere than previously thought.
They appear to play a previously unsuspected and important role in the global nitrogen
cycle, especially in the oceans.3
This eagerness to exploit the anammox bacteria is part of a growing trend in technology
to look to nature for efficient solutions. Scientists are realizing that living
things are full of high-tech surprises, just waiting to be copied and used. In areas
as diverse as weak or strong adhesives (gecko feet and mussels) and streamlining
of motor vehicles (boxfish design), engineers are finding unexpected but highly
useful inventions ready-made for them. Janine Benyus, co-founder of the Biomimicry
Guild, comments:
‘If you have a design problem, nature’s probably solved it already.
After all, it’s had 3.8 billion years to come up with solutions ….
The truth is, natural organisms have managed to do everything we want to do without
guzzling fossil fuels, polluting the planet, or mortgaging the future.’4
Sadly, as this comment illustrates, ‘millions of years’ often takes
the credit for these ingenious natural designs away from the Creator.4
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Related resources
References
- News feature, Nature 437:1227–1228,
2005; Pilcher, H., Microbiology:Pipe dreams;
www.nature.com/nature/journal/v437/n7063/full/4371227a.html.
Return to Text.
- Fuerst, J.,
Planctomycetes: a phylum of emerging interest for microbial evolution and ecology,
Department of Microbiology and Parasitology, University of Queensland, Brisbane,
Australia. Return to Text.
- Dalsgaard, T., Canfield, D.E., Petersen, J. et al.,
N2 production by the anammox reaction in the anoxic water column of Golfo Dulce,
Costa Rica, Nature 422:606–608, 2003.
Return to Text.
- Underwood, A., Nature’s design workshop: engineers turn
to biology for inspiration, Newsweek 146(13):55, 2005.
Return to Text.
- Based on mass balances over anammox enrichment cultures; Strous
M., Heijnen J.J., Kuenen J.G. and Jetten M.S.M., The sequencing batch reactor as
a powerful tool for the study of slowly growing anaerobic ammonium-oxidizing microorganisms,
Appl. Microbiol. Biotechnol. 50:589–596, 1998. Return to Text.
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