| Special
Microbe Fact File
2541/ There are more
microbial cells in our bodies than there are human cells!
In fact 95% of all the cells in the body are bacteria, mainly
living in the digestive tract.
2542/ There are more
bacteria in the colon than the total number of people who
have ever lived.
2543/ Everyone has about
1 kg in weight of bacteria in their gut. Each gram of faeces
contains 100,000,000,000 microbes.
2544/ Human adults excrete
their own weight in faecal bacteria every year.
2545/ Without microbes
we could not digest our food properly. Thanks to the bacteria
inside the colon, which ferment about 100g of food each day,
this part of our digestive tract is probably the most active
organ in the body.
2546/ Microbes - bacteria,
fungi, algae, protozoa and viruses - affect every aspect of
life on earth. They have an amazing diversity of form and
can exist in a wide range of habitats from hot springs to
the icy wastes of Antarctica and inside the bodies of animals
and plants. Microbes cause diseases like 'flu or malaria,
but most are completely harmless. They are essential to the
cycling of nutrients in the ecosystems of the planet. Microbial
activity is exploited for the benefit of humankind in many
ways, such as the production of medicines, food and enzymes,
in the clean-up of sewage and other wastes and in the exciting
advances resulting from developments in molecular biology
techniques.
2547/ In the light of
recent advances in molecular biology, which allow the comparison
of the sequencing of ribosomal RNA of organisms, a new classification
system is preferred by scientists. It is based on three lines
of descent from a common ancestor. Each group is called a
Domain:
1. Bacteria (true bacteria) - prokaryotes
2. Archaea (archaebacteria) - prokaryotes
3. Eukarya - eukaryotes
2548/ The eukaryotes
include fungi, protozoa, algae, plants and all multicellular
animals. Prokaryotes include bacteria and the mysterious archaebacteria
which are prokaryotic in general structure but also share
some characteristics with eukaryotes. Viruses are akaryotic
because they are non-cellular. Prions are not micro-organisms
but they are studied by microbiologists.
2549/ We consume the
edible fruiting bodies of fungi when we eat mushrooms.
2550/ Lactic acid bacteria
are used in the fermentation of milk to produce many dairy
products such as yoghurt and cheese, vegetables to produce
sauerkraut as well as fermented meat products such as salami.
2551/ The microbial genome,
Deinococcus radiodurans, has the remarkable capacity to withstand
massive space-scale doses of over 1.5 million rads of radiation
- 3,000 times the dose that would kill a human in space.
2552/ C. acetobutylicum,
a nonpathogenic microbe that can convert starch into the solvents
acetone and butanol, enjoys an unusual place in history. Discovered
in 1915 by Chaim Weizmann, the microbe was used by Great Britain
during World War I for generating acetone to produce cordite
for artillery shells. In gratitude, the government offered
to honor Weizmann, but he asked instead for British support
of a Jewish homeland in Palestine. This led to the Balfour
Declaration of 1917, committing Britain to sanction what became
in 1948 the state of Israel, with Weizmann as its first president.
2553/ In the warm waters
of the Red Sea, and off the coast of Australia, the largest
bacteria ever seen have been discovered in the guts of a fish.
Epulopiscium fischelsoni is a bacterium of mammoth proportions.
It can sometimes grow as large five hundred micrometers, or
as about the size of the period at the end of this sentence,
which is a remarkable size for bacteria.
2554/ The small size
of most bacteria is owed to their limited abilities. Since
they have few ways to transport nutrients across their cell
membranes, they rely on diffusion to move food into their
cells, and wastes out of them. This process of diffusion is
limited by the surface area of a cell, which is the space
that a cell's surface would occupy if it were stretched out
flat. As a cell gets bigger, both its volume and surface area
increase, but its surface area increases more slowly than
its volume. Above a certain size, there is not enough surface
area to absorb all of the nutrients that the increasing cell
volume needs. So, the limit of a bacterium's size is related
to the proportion of its surface area to its volume.
2555/ Organisms that
use the earth's geomagnetic field have some type of internal
compass. The smallest organisms that use this navigational
method are called magnetotactic bacteria.
2556/ Magnetotactic bacteria
were discovered in 1975 by Richard P. Blakemore. Blakemore
noticed that some of the bacteria that he observed under a
microscope always moved to the same side of the slide. If
he held a magnet near the slide, the bacteria would move towards
the north end of the magnet. These bacteria are able to do
this because they make tiny, iron-containing, magnetic particles.
Each of these particles is a magnet with a north pole and
a south pole. The bacteria arrange these tiny magnets in a
line to make one long magnet. They use this magnet as a compass
to align themselves to the earth's geomagnetic field.
2557/ At the equator,
the geomagnetic north doesn't point up or down, so the magnetotactic
bacteria found there are a mixture of north-seeking and south-seeking
bacteria.
2558/ Deinococcus radiodurans
(said Din-o-coc-us rad-i-o-dew-ranz) was first found in food
in the 1950's - food supposedly sterilized by radiation treatments.
2559/ It has been discovered
that Deinococcus is as resistant to complete dehydration as
it is to radiation. In fact, the same response is elicited
by the organism when exposed to dry conditions as it is when
exposed to high radiation levels, leading researchers to conclude
that the organism evolved to survive long periods of dehydration,
and that the resistance to radiation is only incidental to
the discovery and development of radiation emitting technology
during the second half of this century.
2560/ The first person
to see microbes was a seventeenth century Dutch cloth merchant
named Antoni van Leeuwenhoek. Leeuwenhoek made his own microscopes
by grinding high-quality lenses, which he used to view drops
of blood, pondwater, bits of skin, scrapings from his teeth,
minerals, plant tissue and other samples. He called the tiny
creatures he observed "animalcules." Even before
we knew what they are, we were using microbes to do work for
us, such as leavening bread, turning grapes into wine and
curdling milk to make cheese. Now we have the means to manipulate
microbial genes so that they make industrial enzymes, vitamins
and many important medicines, as well as continue to perform
their centuries old functions in food processing.
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