Chapter 1 Lecture Outline Microbial Life: Origin and Discovery

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. What Is a Microbe? Microbes are microscopic Through most of their lifespan Can only be seen through a microscope Less than about 1 mm across 10-7 m to 10-3 m Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. What Is a Microbe? 6 major groups studied by microbiologists Prokaryotes Bacteria Eukaryotes Algae Viruses Archaea Protists Fungi Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. What Is a Microbe? Microbes are living creatures Except for viruses, which are noncellular Metabolize food, grow, reproduce Have proteins, sugars, nucleic acids Microbial genomes are sequenced Genome = organism’s total genetic content Complete gene sequence known for many species Over 1000 bacteria, over 1000 archaea Tens of thousands of viruses Microbes have greatest diversity of genomes Important for understanding evolution Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbes Shape Human History Microbes affect food availability Destroy crops, but preserve food Bread, wine, cheese Chocolate! Microbial diseases change history Black plague in Europe Smallpox in Americas Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Discovery of Microbes Light microscope invented in 1600s Quality improved continuously Mid-1600s: Robert Hooke observes small eukaryotes 1676: van Leeuwenhoek discovers bacteria Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbes Are Living Organisms Microbes arise only from other microbes No spontaneous generation 1688: Redi shows that flies do not spontaneously generate 1861: Pasteur shows that microbes do not grow in liquid until introduced from outside Flask neck broken, bacteria fall into and grow in medium No growth Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Germ Theory of Disease Observations: Germs can infect and grow on food. Hypothesis: Can germs infect and grow on people? That is, do germs cause disease? Hypothesis is testable: Are germs found in infected tissue? Can transmission of germs cause disease? Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Germ Theory of Disease Pasteur’s Theory: Transmission of germs causes disease All Scientific Theories: Explain many known observations For example, transmission of rabies Provide framework for understanding Where do diseases come from? Can be tested further Do germs cause anthrax? A scientific theory is NOT a “guess” Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Koch’s Postulates Provides means of testing hypothesis: “Does this germ cause that disease?”

Corollary to Germ Theory Stop germ transmission, stop disease spread Stop spread of germs Epidemiology, public health measures Resistant individuals prevent spread of germs 1798: Vaccination with cowpox prevents smallpox Turkish physicians, Lady Montagu, Edward Jenner Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Corollary to Germ Theory Stop germ transmission, stop disease spread Kill germ, prevent disease Antiseptics 1865: Antiseptic surgery Joseph Lister Antibiotics 1929–1941: Penicillin Alexander Fleming Many newer antibiotics Bacteria become resistant Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Microbial Ecology Most microbes don’t grow on typical medium Many live in varied conditions Anaerobic Bottom of swamp, in our gut High pressure Bottom of ocean Hot or cold temperatures Below 0°C to 113°C No organic carbon Use light for energy, CO2 for carbon Microbes existed before animals or plants There was no oxygen in Earth atmosphere Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Microbial Ecology Culture some microbes in natural mud environment Winogradsky column Layers grow different species Reflecting different conditions Can see variations in nature Yellowstone geyser runoff Colors reflect different species Different growth temperatures >56°C <50°C Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Microbial Ecology Microbes cycle most elements on earth Nitrogen cycle Bacteria fix N2 to NH4 Nitrify NH3 to NO3- Carbon cycle Photosynthetic microbes fix most carbon Many other conversions Sulfur cycle Phosphorus cycle Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

The Microbial Family Tree Microbial species are difficult to classify Difficult to distinguish by shape Often reproduce asexually Pass DNA to each other without reproduction Use biochemical properties to classify Gram stain Ability to metabolize different substrates Use DNA sequence to classify Bacterial genomes are relatively small Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

The Microbial Family Tree Archaea are not bacteria Similar size, shape Very different biochemistry Different membranes Archaeal ribosomes similar to eukaryotic ribosomes Many archaea live in harsh environments 16s rRNA gene sequence Found in all creatures Archaea are a separate domain Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Endosymbiont Theory How did eukaryotes arise? DNA similar to archaea’s Mitochondrial, chloroplast DNA Similar to bacterial DNA Endosymbiont theory: Mitochondria WERE bacteria Chloroplasts WERE cyanobacteria Infected or eaten by other species Ended up living together inside Endo-sym-biosis Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Concept Quiz Microbes include members of the following groups: bacteria, animals, protozoa, fungi bacteria, archaea, fungi, viruses archaea, viruses, plants, fungi Answer: B Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Concept Quiz The Germ Theory of Disease provided a framework for understanding how disease could be passed from one individual to another. how mitochondria are descended from bacteria. how microbes regulate global geochemical cycles. Answer: A Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.

Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc. Concept Quiz Analysis of 16s rRNA sequences showed that plants and animals are as distant from bacteria as they are from each other. all microbes are only distantly related to the eukaryotes. archaea are as distant from bacteria as from eukaryotes. Answer: C Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.