Biol 3400
Tortora et al - Chap. 1
An Overview of Microbiology
Microbiology - The study of microscopic life - microorganisms
Why study microorganisms?
What are microorganisms?
I.
What is a cell?
Cells are highly organized structures
An organism’s basic unit of structure and function.
Cell provides for the following essential characteristics of life
• Order
• Reproduction
• Heredity
• Evolutionary adaptation
• Growth and development
• Metabolism
• Response to environment
• Homeostasis
All cells are separated from the external environment by a plasma membrane
All cells contain DNA at some stage in their lifetime. They are storehouses of
information. Cells are also capable of interpreting this information
Where did the first cells come from?
All present day cells have apparently evolved from the same ancestor.
1
Biol 3400
Tortora et al - Chap. 1
II.
Cellular Organization
Unicellular - single cell
e.g., - bacterium
Multicellular - cellular associations and differentiation but lack tissues (next level in the
hierachy of biological organization)
e.g., - filamentous blue green algae
- mushrooms - fungal fruiting bodies
i) Variation in cell size
 Smallest cell - mycoplasma (0.1 to 1.0 µm in diameter)
 Typical bacterial cells - 10 x larger (1 to 10 µm in diameter)
 Eukaryotic cells - 10 x larger than bacteria (10 - 100 µm)
 Largest cell - Ostrich egg yolk - the size of a small orange (5 - 10 cm in diameter)
Notable Exceptions
 Epulopiscium fishelsoni - Bacterial cell 60 X 800 µm
 Thiomargarita namibiensis - Bacterial cell up to 0.75 mm in diameter
 Nanochlorum eukaryotum - eukaryotic algae - cells 1 to 2 µm in diameter
ii) Cell types
Prokaryotic cell
least complex
Eukaryotic cell
most complex
no membrane bound nucleus
membrane bound nucleus
no membrane bound organelles
membrane bound organelles
Domains:
Bacteria and Archaea
Domain
Eukarya
generally smaller
generally larger
2
Biol 3400
Tortora et al - Chap. 1
iii) Viruses
 exception to the rule - acellular
 composed predominantly of protein and nucleic acid - lack cell or plasma membrane
 Not a dynamic open system like a cell
 They have no means of independent life support, rely on host's metabolic machinery
 if infect host they are capable of directing viral reproduction
 infect virtually all living cells
 Smallest virus is 10 nm in diameter; Largest viruses ~ 300 nm in diameter
III
Diversity of Life & Evolutionary Relationships
> 1.8 million species have been identified.
Taxonomy - The branch of biology concerned with the naming (nomenclature) and
classification of organisms.
Systematics - The study of biodiversity in an evolutionary context
Taxonomic Hierarchies
Organizational levels taxon (pl. - taxa)
Ideally
 Represent a coherent degree of homology i.e., genetic and evolutionary similarity
 Members of each taxon should be monophyletic (i.e., same evolutionary history; members of a
genus had a common ancestor)
Taxa
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Species
Scientific Names
3
Biol 3400
Tortora et al - Chap. 1
IV.
Diversity of microorganisms
 Prokaryotes & Eukaryotes
 Metabolism
 Tolerance for extreme environments
V.
Ecology and Microorganisms
 An important consideration is that "populations of cells rarely live alone in nature"
 They usually live in association with other populations - microbial communities
Population - an assemblage of a single type of cells (single species). May be clones of
an original parental cell.

Interactions occur within and between populations and also between the organisms
and their physical and chemical environments (ecosystem)
VI.
Laboratory Culture
 We often grow microorganisms in the laboratory and in order to do this must provide
the appropriate conditions for growth
Culture medium (plural = media) - aqueous solution containing necessary nutrients
 Semisolid medium  agar
Pure culture - a culture containing a single cell type
Sterilization –
Microbes are ubiquitous
 How can you produce a pure culture from a heterogeneous mixture?
Aseptic technique - used to prevent contamination during manipulation of cultures and
sterile media
 Sterilize all media and implements for handling materials of interest
 Clean working area
 Limit exposure to potential sources of contamination
4
Biol 3400
Tortora et al - Chap. 1
Preparation of Pure Cultures
Streak plate technique
 Dilution  Deposition of individual cells or clumps of cells (known as colony forming
units or CFU) on agar medium
 Cell growth  multiplication  resulting in the production of colonies (visible mass
of cells)
 each isolated colony on the streak plate is assumed to have originated from a
single CFU (It is unknown whether the cells in the colony came from a single cell or
a clump of cells)
VII
History
i) First observations of microorganisms
Robert Hooke (1665)
Anton van Leeuwenhoek - 1674 - 1723
Cell Theory
Matthias Schleiden (botanist; 1838) & Theodor Schwann (zoologist; 1839)
i) all living things consist of cells.
ii) all cells come from preexisting cells.
ii) Birth of Microbiology - Late 19th century
Ferdinand Cohn (1828-1898) – founder of bacteriology – mid 1800s
 Discovered genus Bacillus and endospore formation
 Simple methods for preventing contamination of sterile culture media
Louis Pasteur (1822-1895) - father of microbiology – mid to late 1800's
Important discoveries
 Anaerobic life - life without oxygen
 Industrial Microbiology
Ethanol fermentation
Pasteurization
 Vaccines – rabies, anthrax
 Disproved the theory of spontaneous generation
5
Biol 3400
Tortora et al - Chap. 1
Robert Koch (1843-1910)
 Germ theory of disease
Koch's Postulates (Fig 14.3)
• used to prove that a specific type of organism is the cause (etiological agent) of a
specific disease (i.e., Bacillis anthracis and anthrax)
1. The causative agent must be present in all "animals" with the disease and absent
from healthy "animals".
2. The agent of disease can be isolated from the diseased "animal" and can be
cultivated in pure culture in the laboratory
3. The disease can be reproduced by inoculating a portion of the laboratory culture into
healthy "animals".
4. The agent of disease can be re-isolated from the infected "animal" and again
cultivated in the laboratory.

Pure culture technique
iii) Vaccination
Edward Jenner
 Used cowpox virus to vaccinate against smallpox virus
 Vaccines now produced against many infectious agents – vaccines may be live
attenuated or avirulent strains of microorganisms, killed microorganisms or specific
components of the etiologic agents
iv) Chemotherapeutic Agents
 Antimicrobial compounds may be synthetic or isolated from natural sources
(antibiotics)
Antibiotics - substances produced by microorganisms that kill (bacteriocidal) or prevent
the growth (bacteriostatic) of other microorganisms.
Alexander Fleming (Scottish bacteriologist) discovered antibiotics in 1928 with the
discovery of penicillin produced by a fungus called Penicillium chrysogenum
Selman Waksman - early 1940's discovered streptomycin - Streptomyces griseus
6
Biol 3400
Tortora et al - Chap. 1
iv
Microbial Ecology
Early 1900's
Martinus Beijerinck (1851 – 1931)
 nitrogen fixation
 sulfur cycling
 enrichment technique - use of specific culture media and incubation conditions that
favour growth of one type of microorganism while constraining the growth of others.
Sergei Winogradsky (1856 -1953)
 nitrifying bacteria (NH4+  NO2-)
 chemoautotrophs
 The role of microbes in biogeochemical processes
v) Microbial Genetics and Molecular Biology
One Gene - One Enzyme Hypothesis
Beadle and Tatum (1941) Neurospora
DNA - Hereditary Molecule
Bacterial transformation
 Griffith (1928) Streptococcus pneumoniae - transforming principle
 Avery, McCarty, and MacLeod (1944) identified DNA as transforming principle
Transduction
 Alfred Hershey and Martha Chase (1952) - Labelled T2 phage protein or DNA
DNA Structure
 Watson and Crick (1953)
Biotechnology & Recombinant DNA Technology
 Late 1970's until present
7
Biol 3400
Tortora et al - Chap. 1
VII
What is the impact of microorganisms on humans?
1) Environment
 A number of microorganisms are essential for the cycling of nutrients
 We use these microbial processes to treat sewage and remove toxic compounds
from the environment (bioremediation)
2) Disease Agents
 Our bodies are colonized by many different microbial species - normal microbiota
 Diseases are caused by pathogens and diseases caused by microorganisms are
called infectious diseases
 Emerging infectious diseases 3) Agriculture
 Microorganisms affect agricultural productivity in a number of ways
o cause diseases of crop plants and livestock
o may also be beneficial to crop plants and animals
o Biotechnological applications
4) Food Industry
 Microorganisms cause spoilage of food
 Microorganims are also used in the production of a number of food and beverages
5) Biotechnology
 "The industrial use of living organisms or their components to improve human health
and food production" (Campbell et al., 1999)
 "Those processes in which living organisms are manipulated, particularly at the
molecular genetic level, to form useful products" (Prescott et al., 1999)

Biotechnology/Molecular genetics has been used to produce genetically modified
organisms (GMO) for the following applications
o Transgenic crop plants and livestock
o Production of industrial chemicals and enzymes
o Production of pharmaceutical compounds (i.e., insulin)
o Medical treatments (gene therapy)
8