II. Pathways of Discovery in Microbiology. 1.6 The Historical Roots of Microbiology. Robert Hooke and Early Microscopy

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1 II. Pathways of Discovery in Microbiology 1.6 The Historical Roots of Microbiology 1.6 The Historical Roots of Microbiology 1.7 Pasteur and the Defeat of Spontaneous Generation 1.8 Koch, Infectious Disease, and the Rise of Pure Culture Microbiology 1.9 Microbial Diversity and the Rise of General Microbiology 1.10 The Modern Era of Microbiology The Historical Roots of Microbiology Robert Hooke ( ) was the first to describe microbes Illustrated the fruiting structures of molds (Figure 1.9b) Anton van Leeuwenhoek ( ) 1723) was the first to describe bacteria (Figure 1.10b) Further progess required development of more powerful microscopes Ferdinand Cohn ( ) founded the field of bacteriology and discovered bacterial endospores Robert Hooke and Early Microscopy Robert Hooke and Early Microscopy Figure 1.9a Figure 1.9b The van Leeuwenhoek Microscope 1.7 Pasteur and the Defeat of Spontaneous Generation Louis Pasteur ( ) Discovered that living organisms discriminate between optical isomers Discovered that alcoholic fermentation was a biologically mediated process (originally thought to be purely chemical) Disproved theory of spontaneous generation (Figure 1.13) Led to the development of methods for controlling the growth of microorganisms Developed vaccines for anthrax, fowl cholera, and rabies Figure 1.10 Pasteur s Experiment 1

2 The Defeat of Spontaneous Generation: Pasteur s Experiment The Defeat of Spontaneous Generation: Pasteur s Experiment ~1860: Where do microorganisms come from? Spontaneous generation? Heat was used to kill the microbes in liquid Figure 1.13a When dust was prevented from reaching the sterilized liquid, no microbes grew in the liquid Figure 1.13b The Defeat of Spontaneous Generation: Pasteur s Experiment 1.8 Koch, Infectious Disease, and the Rise of Pure Cultures Robert Koch ( ) Definitively demonstrated the link between microbes and infectious diseases Identified causative agents of anthrax and tuberculosis Koch s postulates (Figure 1.15) 15) Developed techniques (solid media) for obtaining pure cultures of microbes, some still in existence today Awarded Nobel Prize for Physiology and Medicine in 1905 Contact with dust resulted in growth of microbes in the liquid disproved spontaneous generation Figure 1.13c Koch s Postulates Koch s Postulates Anthrax, caused by Bacillus anthracis Organism present in blood of all diseased animals cause or result of the disease? Figure 1.15 Conclusion specific organisms cause specific diseases Koch s postulates can be extended beyond disease-causing organisms Figure

3 1.9 Microbial Diversity and the Rise of General Microbiology 1.9 Microbial Diversity and the Rise of General Microbiology General Microbiology Field that focuses on non-medical aspects of microbiology Roots in 20th century Martinus Beijerinck ( ) Developed Enrichment Culture Technique Microbes isolated from natural samples in a highly selective fashion by manipulating nutrient and incubation conditions e.g., Nitrogen-fixing bacteria Sergei Winogradsky ( ) and the Concept of Chemolithotrophy Demonstrated that specific bacteria are linked to specific biogeochemical transformations (e.g., S & N cycles) Proposed concept of chemolithotrophy Oxidation of inorganic compounds linked to energy conservation (Figure 1.19) Major Concepts Conceived by Sergei Winogradsky Major Concepts Conceived by Sergei Winogradsky Figure 1.19a Figure 1.19b Some Landmarks in Molecular Microbiology since 1985 Brock Biology of Microorganisms Twelfth Edition Madigan / Martinko Dunlap / Clark Ch hapter 2 A Brief Journey to the Microbial World Figure 1.20 Lectures by Buchan & LeCleir 3

4 II. Cell Structure and Evolutionary History 2.5 Elements of Cell and Viral Structure Elements of Cell and Viral Structure Arrangement of DNA in Microbial Cells The Evolutionary Tree of Life All microbial cells have the following in common: Cytoplasmic membrane Cytoplasm Ribosomes Internal Structure of Prokaryotic Cell Internal Structure of Eukaryote Cell No organelles Figure 2.11a Figure 2.11b 2.5 Elements of Cell and Viral Structure Electron Micrographs of Sectioned Cells Eukaryotic vs. Prokaryotic Cells Eukaryotes DNA enclosed in a membrane-bound nucleus Cells are generally larger and more complex Contain organelles Prokaryotes No membrane-enclosed organelles No nucleus Generally smaller than eukaryotic cells Figure 2.12a and b 4

5 Electron Micrographs of Sectioned Cells 2.5 Elements of Cell and Viral Structure Viruses Not considered cells No metabolic abilities of their own Rely completely on biosynthetic machinery of infected cell Infect all types of cells Smallest virus is 10 nm in diameter Viruses of bacteria = bacteriophages Yeast cell, 8 μm diameter Figure 2.12c Virus Structure and Size Comparison of Viruses and Cells 2.6 Arrangement of DNA in Microbial Cells Genome A cell s full complement of genes Prokaryotic cells generally have a single, circular DNA molecule called a chromosome DNA aggregates to form the nucleoid region Prokaryotes also may have small amounts of extrachromosomal DNA called plasmids that confer special properties ( i.e., antibiotic resistance) Figure Arrangement of DNA in Microbial Cells The Nucleoid Eukaryotic DNA is linear and found within the nucleus Associated with proteins that help in folding of the DNA Usually have more than one chromosome oso Typically have two copies of each chromosome [Insert Fig. 2.14] Figure

6 2.6 Arrangement of DNA in Microbial Cells The Tree of Life Defined by rrna Sequencing Escherichia coli Genome 4.68 million base pairs 4,300 genes 1,900 different kinds of protein 2.4 million protein molecules Human Cell 1,000X more DNA per cell than E. coli 7X more genes than E. coli Figure The Evolutionary Tree of Life Ribosomal RNA (rrna) Gene Sequencing and Phylogeny Evolution The process of change in a line of descent over time that results in new varieties and species of organisms Phylogeny Evolutionary relationships between organisms Relationships can be deduced by comparing genetic information (nucleic acid or amino acid sequences) in the different specimens Ribosomal RNA (rrna) are excellent molecules for determining phylogeny Can visualize relationships on a phylogenetic tree Figure The Evolutionary Tree of Life 2.7 The Evolutionary Tree of Life Comparative rrna sequencing has defined three distinct lineages of cells called domains. Bacteria (prokaryotic) Archaea (prokaryotic) Eukarya (eukaryotic) Archaea and Bacteria are NOT closely related. Archaea are more closely related to Eukarya than Bacteria. Eukaryotic microorganisms were the ancestors of multicellular organisms Mitochondria and chloroplasts also contain their own genomes (circular, like prokaryotes) and ribosomes These organelles are ancestors of specific lineages of Bacteria Mitochondria and chloroplasts took up residence in Eukarya eons ago This arrangement is known as endosymbiosis 6

7 The Tree of Life Defined by rrna Sequencing Figure