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?