you ever wondered about how small germs are?
And what are germs anyway?
Are you always being
told to wash your hands? Do you know why?
is a microbiology?
means very small and biology
is the study of living things, so microbiology is the study of very
small living things normally too small tobe seen with the naked
science of microbiology started with invention of the microscope
and the English scientist, Robert Hooke,
takes the credit for this.
burnetii bacteria © 1994, The Centre for Microscopy and
microbes are bad for us, aren't they?
It is true that some microbes cause disease and others cause decay
and damage to inanimate objects, but without microbes we would not
be able to exist. Microbes are everywhere and the more we
look the more we find, sometimes in the most unlikely
body is infested with microorganisms and most of them are essential
for our survival. They assist in food digestion in our digestive
system, for instance.
microbes that cause decay are useful
for they breakdown dead matter into simple chemicals, so the matter
can be recycled and used by other - probably more complex - life
forms. Without the decay process, the world would soon be
covered in dead creatures and plants.
have different functions for different purposes and to occupy different
niches in the biology of the planet. They have evolved when
and where they had the opportunity, without any moral imperative.
But as humans, we find that some are useful to us and others are
dangerous to us. So we view them as either good or bad.
microorganisms include those that are necessary to maintain our
environment, in a way that will support our existence. Then
there are our very own microorganisms that our body uses as part
of its internal defense system, to fight infection from outside.
microorganisms enter the body in a number of different ways, but
most commonly by the respiratory and digestive system, or by damaged
skin. They cause problems to the body because they destroy
body tissue and release toxic substances. This upsets the
normal running of the body, which has to divert energy to its internal
defense system in order to fight the invader.
that cause disease include:
examples see Rainforest Diseases and
the Bad Bug Book.
do microbes work?
it should be understood that all living things "work" in the same
way at the most basic level. There are certain structures
and functions that are common to all
living organisms. Likewise all living things use similar chemical
processes to work - this is known as organic chemistry. One
chemical element above all others dominates organic chemistry -
carbon. This has some unique properties that allow trillions
of different chemicals to be made from a few chemical elements.
An account of why carbon is the basis of life is shown here.
us look at some of the key structural and chemical components of
living organisms in general and microbes in particular.
All living organisms are made from cells.
They are the basic unit from which living things are constructed
and the smallest part of an animal or plant that can function independently.
All cells have an outer coat or membrane that is resilient to the
external environment. It is tough and resists damage to the
cell, physically, chemically and biologically. It also provides
a good internal environment with a boundary where life processes
can be performed by the organic chemicals inside the cell.
The boundary is important, too, because that stops the contents
of the cell from being dispersed.
types of cell structure exist Prokaryote
lack a nucleus, and consist of a cell membrane in which several
distinct components function. Typically these are:
- A coiled strand of DNA
Ribosomes - Factory-like elements of a cell, where messenger
RNA is turned into proteins - building blocks and enzymes - the
Cytoplasm - The general cell contents
Glycogen granules - to provide energy
often also possess flagella,
which help them move.
cells have additional internal components, notably a
nucleus and mitochondria.
- Contains the cell's DNA in threads of chromatin
Mitochondria - the cells' powerhouse where energy is released
by aerobic respiration
Choroplasts - cells that contain pigment, such as
chlorophyll, which may play a major role in producing food for the
Plastids - A tiny structure within a plant cell that
performs a particular function. Apart from the nucleus, plastids
are the largest components in the cell.They may containing pigments
in which case they are called chromoplasts,
or they may be colorless (leucoplasts).
They can changes from one type to the other. Both the mitachondria
and the chloroplasts in plants are types of plastid.
© 1999 The Centre for Microscopy and Microanalysis
of Cell Biology
The origins of Mitochodria and Chloroplasts
Ribonuclease Single Crystal © 1995-2000
by Michael W. Davidson and The Florida State University.
are organic catalysts which speed-up an organism's chemical reactions,
without changing themselves. Chemical reactions can often
be speeded up by heating, but in the case of living organisms this
can damage them. The enzyme, which is usually protein with
a specific shape for each purpose, controls the chemical reactions
in the cell and thus allows the organism to metabolize.
are two groups of enzymes: intracellular and extracellular.
The former exist inside cells, controlling the metabolic rate.
The latter are produced by cells, but work outside of these.
For instance, digestive enzymes are used by the body to break down
food in the digestive system.
speed up reactions, without being destroyed by the reaction itself.
They will not work in high temperatures, or at the wrong pH
balance. Each enzyme has a specific function, but it
can work in either direction of the chemical reaction.
enzymes may be used repeatedly almost indefinitely, however organic
enzymes do need to be replenished by the organism at intervals.
is a complex molecule containing instructions for all the functions
of the cells of an organism, its "genetic information". It
replicates itself by separating its two interwoven strands (the
helix) like a zip fastener and attracting free nucleotides (simpler
molecules of nucleic acid) in the same order as the original.
DNA molecule is a double helix made of four types of nucleotide.
These are aligned in a ladder formation, which is twisted like a
screw. On opposite sides of the double helix are companion
nucleotides. Adenine (A)
and Thymine (T) are always
located opposite other, and so are Guanine
(G) and Cytosine (C).
So, each strand of the double helix is a "mirror image" of the other.
This is why A, T, G and C are the four letters associated with the
is the "master copy" for all the instructions for the cells of the
image shows the double helix structure of the DNA, which consists
of two strands with the cross links at intervals joined be hydrogen
bonds. There are ten crosslinks for every complete twist of
the double strand. The lower image shows a section of the
DNA helix, untwisted. It shows the main components of the
strand: Sugars (pentagonal shapes), phosphates (spheres) and organic
bases (A, C, G and T).
replicate, the DNA unzips along the center of the rungs of the ladder.
The exposed free ends can then form two new DNA strands by allowing
"partner" molecules to link at the exposed rungs. A can only
pair with T, and C with G.
the replication process is not perfect. Stands break, or additional
pieces of DNA become inserted, for instance. This is how mutations
occur and evolution happens.
ribonucleic acid, is
a much smaller molecule than DNA, which copies the information and
takes part in the process of protein synthesis in cells.
It differs from DNA in that Uracil (U)replaces
Unlike DNA it can interact with other molecules, specifically ribosomes.
The RNA copy of the DNA information is transcribed from the DNA
template, this is known as transcription
RNA, this is the copied message
of the DNA.
messenger RNA, is a further
copy of the RNA transcript which has been spliced and modified.
It carries the information from the DNA which specifies an amino
acid sequence of proteins. In a eukaryote it then moves out
of the nucleus into the cytoplasm, where it attaches to the ribosome.
In a prokaryote, which does not have a nucleus wall, the next process
takes place on-site. mRNA is the
new message of instructions from the DNA.
the adapter molecule which allows the mRNA nucleotide sequences
to be translated into protein amino acid sequences. The
anticodons link up to their corresponding codons of the mRNA, one
at a time, as the mRNA moves through the ribosome. This
tRNA is the receiver of the message.
occurs with proteins to make up the ribosome
which provides the site for translation to occur. Ribosomes
can be be located in clusters, or as free individuals, depending
upon the final purpose of the altered proteins. Ribosomes
are the "factories" that use the message to make essential
chemicals for a cell to function.
and Genes are very long thread-like structures in the
nucleus of eukaryotic cells, that carry the hereditary information
of the cell. They contain a long length of double-stranded
DNA coiled up - the famous Double Helix,
along with some RNA and special proteins. Bacteria
or prokaryotic cells, only have one chromosome
each, which is not in the nucleus.
are units or factors of inheritance, each one being a length of
DNA containing a particular instruction. For instance your
eventual height is determined by a particular gene.
and Anaerobic Respiration and Fermentation
and animals are strict aerobes, which means they need oxygen to
respire. In simple terms aerobic
respiration is breathing using oxygen. Aerobic
respiration in the cell is a chemical reaction whereby organic compounds
such as glucose, are converted into energy for the cell, using oxygen
from the environment as the final electron acceptor (linking to
hydrogen). The by-products of carbon-dioxide and water are
released back into the environment. (When plants photosynthesize
they use light for their energy and to fix carbon for their own
use from the carbon-dioxide, releasing oxygen as a by-product).
right) Campylobacter: aerobic,
gram-negative bacteria that can cause food poisoning.
© Neal Chamberlain
respiration by contrast is a process whereby
respiration takes place without oxygen. This
occurs only in some groups of bacteria,
living in anaerobic environments such as in soil and stagnant water.
These strict (obligate) anaerobes use
a substance other than oxygen - eg. sulfate, nitrate, carbonate -
as the final electron acceptor.
left) Clostridium difficile:
anaerobic bacteria that can infects the large intestine.
© Neal Chamberlain
Escherichia coli is glucose-fermenting Gram-negative bacteria
© 1994, The Centre for Microscopy and Microanalysis
|Facultative anaerobes, such
as yeasts and many bacteria, can
use either fermentation or aerobic respiration depending on the
availability of oxygen. In fermentation
the cell uses an organic molecule, such as ethanol or lactate, as
the electron acceptor. In the case of alcohol fermentation,
carbon-dioxide is released. Fermentation is less productive
than aerobic respiration as an energy source for cells.
(When animal muscle tissue is required to function without an adequate
oxygen supply there is a build up of lactic acid, which is an example
of lactic acid fermentation - this does not release carbon-dioxide.)
Comparison of relative efficiencies
of different types of respiration:
+ 2880 kJ
sugar + oxygen > water + carbon dioxide
Anaerobic respiration with
ethanol formation (alcohol fermentation):
+ 210 kJ
ethanol + carbon dioxide + energy
Anaerobic respiration with
lactic acid formation (fermentation):
+ 150 kJ
lactic acid + energy
more information use the on-line glossaries for Glycolysis, ATP, Krebs
Cycle and Calvin Cycle
of Microbiolgy - Glossary
of association between and among life forms:
- a relationship between two different
species of organisms, living together in direct contact.
a relationship between two symbionts
that is of mutual benefit, eg lichen (which is not
an individual organism but the symbiosis of cyanobacteria and a
- a symbiotic relationship which
benefits the symbiont
, but has no effect on the host,
eg many of the bacteria living inside and on the surface of the
- absorbing nutrients from a living
organism the symbiont benefits,
but harms the host
- endoparasites live within the host, eg tapeworm;
ectoparasites live outside the host, eg flea.
absorbing nutrients from dead organic matter and decomposing it
in the process, eg methanogens - an anaerobic sub-group
of archaebacteria, used as decomposers for sewage treatment.
Host & Symbiont:
Host - participant
which is exploited by the symbiont.
Symbiont - participant
living in or on the host.
mold spores © 1994, The Centre for Microscopy and Microanalysis
do Microbes Eat?
have many different ways of metabolizing - getting the energy they
need to live, known as nutrition.
means the way an organism acquires two resources - energy and carbon
- with which it synthesizes organic compounds for it to function,
grow, and repair itself. If the species uses light as its
energy source it is called a phototroph,
if it uses energy from chemicals it is a chemotroph.
are organisms that only require
inorganic compounds such as carbon-dioxide for their source of carbon.
are organisms which require at
least one organic nutrient from organisms, or their by-products,
as a carbon source for producing their own organic compounds.
to their sources of carbon and energy, bacteria can be divided into
four major groups: photoautotrophs,
photoheterotrophs, chemoautotrophs and chemoheterotrophs.
are photosynthetic bacteria and cyanobacteria
up carbon-dioxide and water into organic cell materials using energy
from sunlight. One product of this process is starch, which
is a storage or reserve form of carbon, which can be used when light
conditions are too poor to satisfy the immediate needs of the organism.
Photosynthetic bacteria have a substance called bacteriochlorophyll,
live at the bottom of lakes and pools, and use the hydrogen from
hydrogen-sulphide instead of from water, for the chemical process.
pigment absorbs light in the extreme UV and infra-red parts of
the spectrum which is outside the range used by normal chlorophyll).
and green sulfur bacteria
use light, carbon-dioxide and hydrogen-sulphide from anaerobic decay,
to produce carbohydrate, sulfur and water. Cyanobacteria
live in fresh water, seas, soil and lichen, and use a plant-like
photosynthesis which releases oxygen as a by-product.
© 1997, Microbial Diversity
light, but obtain their carbon in organic form. Only certain
types of prokaryotes can do this. The first life on Earth
may have been of this type, using organic material such as amino
acids not produced by biological activity.
include many bacteria. They use special chemical processes
instead of sunlight to produce organic material from inorganic.
Usually compounds other than sugar are oxidized for the chemical
process. Colorless sulfur bacteria
which live in decaying organic matter where they are unable to use
sunlight, oxidize the hydrogen-sulphide given off, to form water
and sulfur. Iron bacteria,
which live in streams that run over iron-rich rocks, oxidize the
iron salts. Hydrogen bacteria
can oxidize hydrogen with the formation of water.
Nitrifying bacteria are
important for enriching soil with nitrogen in a form that can be
used by plants. (See nitrification and denitrification).
need organic molecules for providing
energy and carbon. They are most commonly bacteria, but also
protists, fungi, animals and some plants. Chemoheterotroph
bacteria can be saprobes
which absorb their nutrients from from dead organic matter, thus
decomposing it, or mutualists
which absorb their nutrients from the body fluids of living hosts.
is a chemoheterotroph.
saprophytic species of penicillium - mold on orange
and de-nitrification: Most
of the ammonia from decayed animal and plant proteins in the
soil is used by bacteria such as nitrosomonas and
nitrococcus as an energy source. This activity oxidizes
ammonia to nitrite whereupon other bacteria, nitrobacter,
oxidize the nitrite to nitrate in a process called nitrification.
Nitrate released from this process can be assimilated by plants
through their roots and converted to organic form such as amino
acids and proteins. Animals, however, can only assimilate
organic nitrogen by eating other animals or plants.
bacteria obtain the oxygen they need for metabolism from nitrate
instead of oxygen. This results in the denitrification
process, whereby some nitrate is converted back to nitrogen and
returned to the atmosphere.
Food Chain or Food Web: is
the process by which biomass is recycled. This involves the
movement or cycling of organic chemicals through the environment,
ie the movement of carbon, nitrogen, oxygen and water, through plants,
animals, fungi, bacteria, etc by respiration
and metabolism. For the processes involved, see
Cycling Chemicals and Rainforest
© 1999 The Centre for Microscopy and Microanalysis
small are microbes?
are extremely small but how small? They are so small that
we cannot normally see them. You could fit many thousands
on this full stop .
us consider a typical bacterium. How big is it and what would
would be something like 0.003 mm long and it would weigh
are even smaller and recently nanobacteria
a hundred times smaller than common bacteria, have been found.
At the other end of the scale, giant bacteria are known. One,
is 0.06 mm long and 0.008 mm wide.
visit the Size comparison page.
do we see them if they are so small?
use microscopes to see individual microorganisms,
but it is possible to see colonies with the naked eye. Yeasts
and molds are easy to see, as are the matted strands of algae.
But in such instances you will be looking at thousands of individuals.
to see microbes. It is possible
to detect individual microbes with the naked eye by employing a
little trick. Look at a well-lit blank space - the sky or
a white wall, for instance. Close one eye and partly close
the other. De-focus and you should be able to see faint stringy
strands on the surface of the eye that look like beads. Some
of these are almost certainly bacteria such as streptococci.
Space Station Biomedical
1999 Satellite Events Enterprises Inc.