Introduction
• Microbes, or microorganisms, are minute
living things that are too small to be seen
individually without a microscope
• The group includes bacteria, fungi (moulds
and yeasts), protozoa and microscopic algae
• Viruses are also microorganisms (non cellular
– alive or not?)
Majority are beneficial
• The vast majority of microorganisms are
beneficial eg
– Marine and freshwater microorganisms
– Soil microbes
– Photosynthesis
– Gut bacteria
– Commercial applications – medicines, plastics,
food industry
Minority are pathogenic
• Pathogenic = disease producing
• Many diseases caused by microorganisms
• Some only affect some groups (elderly, sick,
immune compromised)
• Most are treatable
• Some diseases and epidemics and pandemics
have changed the world
Naming and classifying
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Binomial classification
Genus name and specific epithet
Both names underlined or italicised
By custom, after a scientific name has been
mentioned once it can be abbreviated with
the initial of the genus followed by the specific
epithet
• eg Staphylococcus aureus = S. aureus
Types of microorganisms
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Bacteria
archaea
fungi
protozoa
algae
viruses
Bacteria
• Singular = bacterium
• Relatively simple single celled (unicellular)
organisms
• Genetic material not enclosed in a special
nuclear membrane = prokaryotes
• Shapes include rods (bacillus), coccus
(spheres) or spiral or even stars or squares
Bacteria
• May form pairs, chains, clusters or other shapes
• Enclosed in peptidoglycan (protein +
carbohydrate) cell walls
• Generally reproduce by dividing into two equal
cells = binary fission
• Most use organic chemicals as food
• Some can manufacture their own food by
photosynthesis
• Some ‘eat’ inorganic substances
• Many can ‘swim’ using flagella
Archaea
• Archaea consist of prokaryotic cells but cells
walls (if they have them) are not
peptidoglycan
• Archaea are often found in extreme
environments
• Archaea are divided into three main groups
– Methanogens
– Extreme halophiles
– Extreme thermophiles
Fungi
• Fungi are eukaryotes = have a distinct nucleus
containing the cell’s genetic material
surrounded by a special envelope called the
nuclear membrane
• Fungi may be unicellular or multicellular
• Do not photosynthesise
• Cell walls comprised of chitin
• Yeasts are unicellular forms of fungi
Fungi
• Molds are funig that form visible masses
called mycelia composed of long filaments
(hyphae)
• Funig can reproduce sexually or asexually
• They get nutrients by absorbing solutions of
organic material from their environment
• Organisms called slime molds have
characteristics of both fungi and amoebas
Protozoa
• Unicellular eukaryotic microbes
• Protozoa move by pseudo pods, flagella or
cilia
• Protozoa have a variety of shapes and live
either as free entities or parasites
• Protozoa can reproduce sexually or asexually
Algae
• Algae are photosynthetic eukaryotes with a
wide variety of shapes and both sexual and
asexual reproductive forms
• Many algae have cell walls made of cellulose
• Found in fresh and salt water, in soli and in
association with plants
• As they photosynthesise they need light,
water and carbon dioxide
• They produce oxygen and carbohydrates
Viruses
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Viruses are different to the other microorganisms
Very small (electron microscope needed)
Acellular (not cellular)
Virus particle has a core made up of one type of
nucleic acid (RNA or DNA)
• The core is covered with a protein coat
• Sometimes the coat is covered with an extra lipid
layer (called envelope)
Why is this strange?
• All living cells have RNA and DNA and can carry
out chemical reactions and can reproduce as self
sufficient units
• Viruses can only reproduce by using the cellular
machinery of other
Whyorganisms
is this strange?
• Thus viruses are considered to be living when
they multiply within the host cells they infect
• In this sense viruses are parasites
• Viruses are not considered to be living because
outside cells they are inert
Classification
• Before the existence of microorganisms was
known, all organisms where grouped into
either the animal kingdom or the plant
kingdom
• When microorganisms were discovered a new
system was required
• In 1978 Carl Woese devised a system of
classification based on the cellular
organisation of organisms
Three domains
1. Bacteria (cell walls peptidoglycan)
2. Archaea (cell walls, if present, lack peptidoglycan)
3. Eukarya- includes:
– Protists (slime molds, protozoa and algae)
– Fungi (unicellular yeasts, multicellular molds,
mushrooms)
– Plants (includes mosses, ferns, conifers, and
flowering plants)
– Animals (includes sponges, worms, insects and
vertebrates)