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Transcript
Chapter 1 Microbial Life: Origin and Discovery What Is a Microbe? Microbes are microscopic organisms Through most of its lifespan Can only be seen through a microscope mm (10-3 m) to 0.2 μm (2x10-7 m) Usually single-celled Self-contained genome Capacity to reproduce What Is a Microbe? Exceptions exist 1. Super-sized microbial cells Thiomargarita namibiensis “sulfur pearl of Namibia” Caulerpa taxifolia “killer algae” with acres of single cell 2. Microbial communities multicellular assemblages: biofilm, mushrooms microscopic worms and arthropods NOT microbes 3. Living? viruses viroids prions What Is a Microbe? 6 major groups studied by microbiologists Prokaryotes Bacteria Archaea Eukaryotes Algae Viruses Protists Fungi What Is a Microbe? Microbial genomes are easily sequenced Genome = organism’s total genetic content Complete gene sequence known for many species Over 1000 bacteria, archaea Tens of thousands of viruses First sequenced genomes Bacteriophage ΦX174 (1977) Haemophilus influenzae (1995) Saccharomyces cerevisiae (1996) Microbes have greatest diversity of genomes Important for understanding evolution Comparative genomics shows core genes Why study microorganisms? Microbes Shape Human History Microbes affect food availability Destroy crops, preserve food bread, wine, cheese Chocolate! Microbial diseases change history Black plague in Europe Smallpox in Americas HIV/AIDS worldwide Discovery of Microbes Light microscope invented in 1600s Quality mid-1600s: Robert Hooke observes small eukaryotes (mold) Saw improved continuously “cells” in cork 1676: Antoni van Leeuwenhoek discovers bacteria First to see single-celled microbes Microbes Are Living Organisms Microbes arise only from other microbes No spontaneous generation 1688: Francesco Redi shows that maggots do not spontaneously generate 1861: Louis Pasteur shows that microbes do not grow in liquid until introduced from outside Contradiction by John Tyndall: Boiled broth still spoil Contaminated with endospores Germ Theory of Disease Observations: Germs can infect and grow on food. Hypothesis: Can germs infect and grow on people? i.e. Do germs cause disease? Hypothesis is testable: Are germs can be found in infected tissue? Can transmission of germs cause disease? Germ Theory of Disease Pasteur’s Theory: Transmission of germs causes disease All Scientific Theories: Explain e.g. Transmission of rabies Provide framework for understanding Where do diseases come from? Can many known observations be tested further Do germs cause anthrax? A scientific theory is NOT a “guess” Koch’s Postulates Provides means of testing hypothesis: “Does this germ cause that disease?” Organism must meet 4 criteria: 1. 2. 3. 4. Microbe always present in diseased Absent in healthy Microbe is grown in pure culture No other microbes present. Introduce pure microbe into healthy individual Individual becomes sick Same microbe re-isolated from now-sick individual 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 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 Microbial Ecology Most microbes don’t grow on typical medium Many Anaerobic Bottom of ocean Hot or cold temperatures bottom of swamp, in our gut High pressure live in varied conditions Below 0°C to 113°C No organic carbon Use light for energy, CO2 for carbon Microbes existed before animals, plants Early earth contained mainly reduced compounds, such as ferrous iron, methane, ammonia Microbial Ecology Culture some microbes in natural mud environment Winogradsky column Layers grow different species Reflects different conditions Can see variations in nature Yellowstone geyser runoff Colors reflect different species Different growth temperatures >56°C <50°C Microbial Ecology Microbes cycle most elements on earth Nitrogen cycle Bacteria fix N2 to NH4+ Nitrify NH4+ to NO3 Carbon cycle Photosynthetic microbes fix most carbon Many other conversions Sulfur cycle Phosphorus cycle 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 relatively small 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 is a separate domain Endosymbiont Theory How did eukaryotes arise? DNA similar Mitochondrial, chloroplast DNA Similar to archaea’s 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 Cell Biology Techniques Electron microscopy Observation of cell components Eukaryotic organelles Membranes Ultracentrifuge Separation of cell components Study of biochemistry of organelles Fluorescence microscopy Identification of cell components Subcellular location of individual proteins Genetics and DNA Revolution Molecular genetics depends on bacteria Concept of “gene” proposed for bacteria DNA structure Genetic code Transcription, translation Restriction enzymes Recombinant DNA Cloning PCR reaction E. coli has best understood genome