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ALGAE IN DARKNESS Posted by AlgaeNova on Wed March 16 2011 10:19:50 AM 33

The
world’s oceans teem with unicellular algae that carry out
photosynthesis in the sunlight. It has been known for a while that the
particularly abundant diatoms (unicellular algae with a silicate
frustule) are also able to survive in the dark bottom of the ocean,
where neither photosynthesis nor respiration with oxygen is possible.
Scientists of the Max Planck Institute for Marine Microbiology now
disclose this artifice of the algae in the journal Proceedings of the
National Academy of Sciences: In darkness, the diatoms breathe with
nitrate in place of oxygen.
Microalgae
often measure only a few hundredths of a millimeter, but due to their
vast abundance in the world’s oceans they are responsible for about 40%
of the marine primary production, i.e., the biomass production via
carbon dioxide fixation in the sunlight. They often appear as massive
blooms near the sea surface or as greenish-brownish meadows on the sea
floor, if still reached by sunlight. However, diatoms (unicellular algae
with a silicate frustule) are also able to survive in the absence of
sunlight and oxygen, for instance, buried in the sea floor. Anja Kamp,
Dirk de Beer, Jana L. Nitsch, Gaute Lavik, and Peter Stief, scientists
at the Max Planck Institute for Marine Microbiology in Bremen cultivated
several diatom species in the laboratory to explore the metabolic
process that allows the tiny algae to survive in darkness. A correlation
was found between the nitrate that is stored by a diatom cell and its
ability to survive in the absence of sunlight and oxygen. The more
nitrate the cell contained, the longer it could survive in darkness
where the cell does not have the possibility to produce oxygen via
photosynthesis for its own respiration. In experiments with the
coffee-bean-shaped diatom Amphora coffeaeformis, the scientists proved
that diatoms use the nitrate stored in their cells for respiration in
the absence of oxygen. Within just one day, most of the stored nitrate
is used up, converted to ammonium, and excreted by the cell. A key
finding of the Max-Planck scientists was that diatoms use nitrate just
for respiration rather than for biomass production, as would be the case
in sunlight. Anja Kamp says: “The rapid consumption of nitrate and the
absence of biomass production tell us that nitrate respiration in
diatoms is a metabolic process that only serves to prepare the cell for a
resting stage and therefore nitrate respiration is not sustained for
longer time periods.”

In bacteria, nitrate respiration in the absence of oxygen is nothing
exceptional, as many of the bacteria studied at the Max-Planck-Institute
are able to breathe with nitrate, sulfate, or even iron compounds. It
is more spectacular to discover that algae, i.e., organisms with a cell
nucleus, are able carry out both photosynthesis and nitrate respiration,
each under different environmental conditions. These results have just
been published in the renowned interdisciplinary journal Proceedings of
the National Academy of Sciences.

For more information follow this link: http://idw-online.de/en/news413265