Lecture 2Lecture 2

• 1.5 The Historical Roots of Microbiology1.5 The Historical Roots of Microbiology• 1.6 Microbial Diversity and the Advent of 1.6 Microbial Diversity and the Advent of

Molecular MicrobiologyMolecular Microbiology• 2.1 Elements of Cell and Viral Structure2.1 Elements of Cell and Viral Structure• 2.2 Arrangement of DNA in Microbial Cells2.2 Arrangement of DNA in Microbial Cells• 2.3 The Tree of Life2.3 The Tree of Life

Also refer to Table 1.1

Louis Pasteur ~1860Louis Pasteur ~1860Where do the microorganisms come from?Where do the microorganisms come from?Spontaneous generation?Spontaneous generation?

Heat was used to kill the microorganisms in the liquidHeat 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 When dust was prevented from reaching the sterilized liquid, no microorganisms grew in the liquidmicroorganisms grew in the liquid

(Madigan et al., Fig. 1.11)

Contact with dust resulted in growth of microorganisms in the liquidContact with dust resulted in growth of microorganisms in the liquid→→ disproved spontaneous generationdisproved spontaneous generation

(Madigan et al., Fig. 1.11)

Robert Koch, 1870s: Proof that microorganisms can cause diseaseRobert Koch, 1870s: Proof that microorganisms can cause disease--“germ theory of disease”“germ theory of disease”

Anthrax, caused by Anthrax, caused by Bacillus anthracisBacillus anthracisOrganism present in the blood of all diseased animalsOrganism present in the blood of all diseased animals

- - causecause oror resultresult of the disease? of the disease?

(Madigan et al., Fig. 1.12)

Pure culturePure culture

(Madigan et al., Fig. 1.12)

(Madigan et al., Fig. 1.12)

Conclusion - Conclusion - specific organisms cause specific diseasespecific organisms cause specific disease

Koch’s postulatesKoch’s postulates can be extended beyond disease-causing organisms can be extended beyond disease-causing organisms

(Madigan et al., Fig. 1.12)

comparative structure of prokaryotic and eukaryotic cells:

prokaryotic:• nucleoid• no organelles

eukaryotic:• nucleus• organelles

(Madigan et al., Fig 2.1)

bacterial cell, 1 x 3 μm(Heliobacteriummodesticaldum)

(Madigan et al., Fig. 2.2)

yeast cell, 8 μm dia(Saccharomyces cerevisiae)

viruses: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:

(Madigan et al., Fig. 2.6)

ribosomal RNA (rRNA) gene sequencing and phylogeny:

• 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 LifeThe “Five Kingdoms” of Life• Plants• Animals• Fungi• Monera (prokaryotes)• Protists (slime molds, flagellates, Giardia)

• human-centric organization

The Three Domains of LifeThe 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

 CulturalMorphology

Microscopic Morphology

CellularComponents

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 Nitrogenrequirements

DNAsequence

Pigmentation Arrangement Capsule Temperature requirements

Sulfurrequirements

RNAsequence

   Internal Structures

   Symbiotic lifestyle

Fermentation Probes

  AccessoryStructures

   Antibiotic sensitivity

Respiration PCR

    

  

  

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