Lecture 2
• 1.5 The Historical Roots of Microbiology
• 1.6 Microbial Diversity and the Advent of
Molecular Microbiology
• 2.1 Elements of Cell and Viral Structure
• 2.2 Arrangement of DNA in Microbial Cells
• 2.3 The Tree of Life
Also refer to Table 1.1
Louis Pasteur ~1860
Where do the microorganisms come from?
Spontaneous generation?
(Madigan et al., Fig. 1.11)
Heat was used to kill the microorganisms in the liquid
(Madigan et al., Fig. 1.11)
When dust was prevented from reaching the sterilized liquid, no
microorganisms grew in the liquid
(Madigan et al., Fig. 1.11)
Contact with dust resulted in growth of microorganisms in the liquid
→ disproved spontaneous generation
Robert Koch, 1870s: Proof that microorganisms can cause disease
-“germ theory of disease”
(Madigan et al., Fig. 1.12)
Anthrax, caused by Bacillus anthracis
Organism present in the blood of all diseased animals
- cause or result of the disease?
Pure culture
(Madigan et al., Fig. 1.12)
(Madigan et al., Fig. 1.12)
(Madigan et al., Fig. 1.12)
Conclusion - specific organisms cause specific disease
Koch’s postulates can be extended beyond disease-causing organisms
comparative structure of prokaryotic and eukaryotic cells:
(Madigan et al., Fig 2.1)
prokaryotic:
• nucleoid
• no organelles
eukaryotic:
• nucleus
• organelles
bacterial cell, 1 x 3 μm
(Heliobacterium
modesticaldum)
(Madigan et al., Fig. 2.2)
yeast cell, 8 μm dia
(Saccharomyces cerevisiae)
viruses:
• very small microorganisms (10s of nm dia), but not cells
• not dynamic open systems
• do not take nutrients or expel wastes
• static structure; behave as more-or-less as particles, except when infecting host
• possess genes but no biosynthetic machinery
• rely on host machinery to reproduce
• viruses known to infect all cells
• viruses of bacteria = bacteriophages
•see Madigan et al., Fig. 2.3a, b
relative sizes of different microorganisms:
ribosomal RNA (rRNA) gene sequencing and phylogeny:
(Madigan et al., Fig. 2.6)
• all organisms possess ribosomes → rRNAs useful molecules for assessing
relationships between organisms
• rRNA genes isolated
• gene sequences determined and compared
• phylogenetic tree depicts differences between organisms analyzed
The “Five Kingdoms” of Life
•
•
•
•
•
Plants
Animals
Fungi
Monera (prokaryotes)
Protists (slime molds, flagellates, Giardia)
• human-centric organization
The Three Domains of Life
Nomenclature
• Bacteria are named using the binomial system
used for other living things whereby each
species is given two names
• The first name is the Genus name (equivalent to
your surname) and the second name is the
species name (equivalent to your Christian
name)
• Bacteria belong to the one species if they have
90% similarity of all observed characteristics
• A group of similar species that have 80%
similarity is called a Genus
Names and morphology
• The genus name always start with a capital letter and the
species name is in lower case and in singular
• e.g. Staphylococcus aureus
• Such binomial species names are always underlined or written in
Italics
• e.g. Staphylococcus aureus
•
• e.g. not all streptococci are Streptococcus in fact some
streptococci are Leuconostoc
• And not all staphylococci are Staphylococcus in fact some
staphylococci are Micrococcus
• not all bacilli are Bacillus in fact some bacilli are Chlostridium etc
etc.
Criteria for Classification of Prokaryotes
Microscopic
Morphology
Cellular
Components
Growth
Characteristics
Metabolic
Pathways
Molecular
Genetics
Location in
Broth
Cell Shape
Cell Wall
Atmospheric
requirements
Carbon
requirements
DNA base
ratio
Colony
Appearance
Cell Size
Gram Stain
pH tolerance
Nitrogen
requirements
DNA
sequence
Pigmentation
Arrangement
Capsule
Temperature
requirements
Sulfur
requirements
RNA
sequence
Internal
Structures
Symbiotic
lifestyle
Fermentation
Probes
Accessory
Structures
Antibiotic
sensitivity
Respiration
PCR
Cultural
Morphology
End Products