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Introduction to microbiology
Ian Collacott
What is microbiology?
“Microbiology is the study of all living
organisms which are too small to be
visible with the naked eye”
(Microbiology Society:
https://microbiologysociety.org/why-
microbiology-matters/what-is-
microbiology-.html )
• What is science?
• “Science is the pursuit and application of
knowledge and understanding of the natural
and social world following a systematic
methodology based on evidence.”
(https://sciencecouncil.org/about-science/our-
definition-of-science/)
• Evidence is obtained by observation,
experimentation and measurement.
• Scientific knowledge is constantly subject to
amendment and change as new evidence is
accumulated through the scientific method.
Some basic biology… All living organisms are made up of cells.
Biology makes some fundamental and
important classifications.
All species can be classified as either
unicellular (organisms which consist only of
one cell), or multicellular (organisms which
consist of more than one, and usually many,
cells).
Microbes, or micro-organisms, are (mainly)
single-celled life forms.
Taxonomy (classification)
• To make sense of most things in life, a
system of classification is needed. Science in
general, and biology in particular, is no
different.
• First biological system was proposed by the
Swedish botanist Carolus Linnaeus in works
between 1735 and the 1750s. This binomial
system is still in use today.
• Each organism has two (Latin) names, written
in italics. The first is the genus, the second
the species name.
Some more basic taxonomy…
The most fundamental division in biology is
between eukaryotes and prokaryotes.
Eukaryotic cells make up the bodies of all
multicellular organisms, as well as some
single-celled microorganisms. Eukaryotic cells
have a nucleus (and other organelles) which
are enclosed by membranes.
Prokaryotic cells are unicellular organisms.
The cells are very simple, and their “nucleus”
and other organelles are not surrounded by
membranes.
Heirarchical classification
The “tree of life”
Viruses and the “Tree of life”
Note that the previous slides hold no place for
viruses. This is for several reasons.
•Our classification system covers all cellular
life, and a common ancestor for all life forms
is implicit in the system.
•Viruses evolved from cellular life, rather than
the other way round.
•Are viruses “alive”? They do nothing when
outside a host cell.
•However, they can evolve within host cells,
and can be “killed” by heat, disinfectants etc.
Microorganisms
Current classification divides microorganisms
into 7 groups.
•Eukaryotic organisms: algae, fungi, protozoa
and helminths
•Prokaryotic organisms: archaea, bacteria and
viruses
•Study of microorganisms has mainly been
done for practical purposes – diagnosis and
treatment of human and animal/plant
diseases, and industrial use e.g. brewing
• Microorganisms are the oldest forms of life on
earth.
• The first microorganisms probably date to
between 3 and 4 billion years ago (Gya). The
age of earth is approximately 4.54 billion
years. All life forms were microorganisms until
around 1.5 Gya ago. Well preserved bacterial
fossils dating to around 3.5 Gya have been
found in Australia.
• Microorganisms account for much more of
the earth’s total biomass than all animals.
• Microorganisms may be free-living.
• They may be mutualists (microorganism and
host benefit e.g. fungi + plants).
• They may be commensal (the
microorganism benefits, but no benefit or
damage is caused to the host e.g. skin
bacteria).
• They may be pathogens or parasites (the
microorganism benefits, and the host is
harmed – e.g. influenza virus, tuberculosis,
tapeworms).
Algae • Are eukaryotic, may be unicellular or
multicellular, and are a very diverse group.
• A common characteristic is that they are all
able to photosynthesise (use light energy to
produce chemical energy, as plants do).
Fungi
• Are eukaryotic, may be unicellular or
multicellular, and are a very diverse group
(from yeasts to mushrooms).
• A unique feature is that their cell walls contain
chitin (a polymer of a simple sugar).
Protozoa
• Are eukaryotic, unicellular, and are a diverse
group. One definition is “any eukaryotic
organism which is not a plant, animal or
fungus”.
• They may be free-living or parasites.
Helminths • Are eukaryotic, multicellular parasitic worms.
Adults of some species are visible with the
naked eye. Eggs are usually invisible. Many
are common parasites in tropical regions.
• Threadworm infections are common in the
UK.
Archaea
• This group of prokaryotic organisms was only
recognised to be separate from the bacteria
in the 1970s. They differ from bacteria in
some metabolic pathways, and chromosome
expression.
• Many are extremophiles.
Bacteria
• Are prokaryotic, unicellular organisms, and
the simplest life form capable of independent
life. They form a hugely diverse group, living
in all environments.
• They may cause significant illness.
Viruses • The simplest known life form, no independent
metabolism. A hugely diverse group, infecting
(probably) all species. Outcome of infection
ranges from no symptoms to death.
Rabies virus Influenza virus
Summary • Specific terminology, and classification
systems are required to make sense of
biology.
• Microorganisms are the most ancient life
forms on earth.
• They are classified into 7 main groups, 6 of
which are cellular life forms. They are hugely
diverse, and in evolutionary terms highly
successful.
• Despite their tiny size, they have a huge
impact on human life (and are a fascinating
topic for study).
Possible future topics:
• Further discussion of each main microbial
type
• Further discussion of infectious nature of
microorganisms and the diseases they cause
• Discussion of the non-medical/healthcare
related aspects of microbiology
• Non-microbiological topics?
• Thoughts?