MARVEL AT DISCOVERY OF GIANT ORGANISM
July 14, 2013
Blue whales reach a length of 100 feet and are the biggest animals on
earth as far as scientists know. But several years ago you wrote about
some type of microorganism that got enormous as well. What was the story?
In 1999 a type of bacteria a hundred times larger than any other known
bacteria was discovered in the Atlantic Ocean off the coast of Namibia
in southwestern Africa. Compared to other bacteria, that would be equivalent
to a whale more than a mile long.
of the Max Planck Institute for Marine Microbiology in Germany reported
finding a new species that approached the enormous size (for bacteria)
of a period (like the one at the end of this sentence). Schulz and her
research team were amazed to find the previously unknown giant in samples
taken more than 300 feet deep in ocean sediments. "These giant
bacteria grow as a string of pearls," they said in Science magazine,
"which shine white ... and are large enough to be visible to the
naked eye." Yet each individual of the species has only one cell.
bacterium was given a big name - Thiomargarita namibiensis (which
means "sulfur pearl of Namibia"). The species belongs to a
group known as sulfur bacteria that thrive on sulfur compounds from
which they obtain energy. However, whereas some sulfur bacteria require
oxygen for the energy conversion process, the giant bacteria live in
sediments with little or no oxygen present. Thiomargarita rely
instead on nitrogen compounds. Thiomargarita live in deep waters
where both sulfur and nitrogen accumulations can be high, but both elements
may not always be abundant at the same time. Hence, the bacteria often
store one or the other until suitable levels of both are available.
The enormous size of Thiomargarita bacteria is explained as a
necessity for storage while the organism waits out periods when either
nitrogen or sulfur compounds are in short supply.
large size of the single cells of Thiomargarita was at first
a mystery in itself. For species such as bacteria that do not breathe
with lungs or gills, the factor limiting an increase in body size is
a phenomenon known as volume to surface ratio. That is, the maximum
volume of the organism is constrained by the ability of the organism's
surface to provide the necessary exchange of gases with the surrounding
to surface ratio results in a physical law in which the bulk of an object
increases at a proportionally greater rate than its surface. Thus, the
ultimate size the organism can reach is limited. The volume to surface
ratio is also one factor limiting the size of lungless animals like
insects, assuring that most must remain small because the required oxygen
must diffuse from the outside surface of the body to the inside.
size of Thiomargarita is accomplished as a result of a hollow
interior, where the sulfur and nitrogen compounds are stored. The actual
living matter of the cell forms a thin layer with a typical outside
surface area but also an inside surface area that is available for gas
exchange. Therefore, the volume to surface ratio differs from that of
the smaller bacteria that can only use the outer surface.
of such a bacterium offers prospects for controlling certain forms of
water pollution. A bacterial species that thrives on high levels of
nitrates and sulfides that are harmful to most animal species could
be very useful. The bacteria convert the harmful compounds into harmless
sulfur and nitrogen, thus cleansing the habitat. Such systems of biological
control are seldom understood and developed overnight, but research
directed at such a problem could result in major strides in environmental
cleanup technology, which is encouraging news.
even greater interest is the fact that the existence of such a phenomenal
organism was unknown until the last decade of the millennium. What else
is out there that we still know nothing about?
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