chapter 1 microbial life: origin and discovery. what is a microbe? microbes are microscopic...
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Chapter 1
Microbial Life: Origin and Discovery
What Is a Microbe? Microbes are microscopic organisms
Through most of its lifespanCan only be seen through a microscope
mm (10-3 m) to 0.2 μm (2x10-7 m)
Usually single-celledSelf-contained genome
Capacity to reproduce
What Is a Microbe? Exceptions exist1. Super-sized microbial cells
Thiomargarita namibiensis
“sulfur pearl of Namibia” Caulerpa taxifolia
“killer algae” with acres of single cell
2. Microbial communitiesmulticellular 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
Eukaryotes Algae
Viruses
Archaea
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
© 2008 W.W. Norton & Company, Inc. MICROBIOLOGY 1/e
Why study microorganisms?
Microbes Shape Human History Microbes affect food availability
Destroy crops, preserve food bread, wine, cheese Chocolate!
Microbial diseases change historyBlack plague in EuropeSmallpox in AmericasHIV/AIDS worldwide
Discovery of Microbes Light microscope invented in 1600s
Quality improved continuously
mid-1600s: Robert Hooke observes small eukaryotes (mold) Saw “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 generation1688: Francesco Redi shows that maggots do
not spontaneously generate1861: 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 many known observations e.g. 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”
Koch’s Postulates Provides means of testing hypothesis:
“Does this germ cause that disease?” Organism must meet 4 criteria:
1. Microbe always present in diseased Absent in healthy
2. Microbe is grown in pure culture No other microbes present.
3. Introduce pure microbe into healthy individual Individual becomes sick
4. 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 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, plants Early earth contained mainly reduced compounds,
such as ferrous iron, methane, ammonia
Microbial Ecology Culture some microbes in
natural mud environmentWinogradsky column
Layers grow different species Reflects different conditions
Can see variations in nature Yellowstone geyser runoff
Colors reflect different species Different growth temperatures
<50°C
>56°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 cyclePhosphorus cycle
The Microbial Family Tree Microbial species are difficult to classify
Difficult to distinguish by shapeOften reproduce asexuallyPass DNA to each other without reproduction
Use biochemical properties to classifyGram stainAbility to metabolize different substrates
Use DNA sequence to classifyBacterial genomes relatively small
The Microbial Family Tree Archaea are not bacteria
Similar size, shapeVery 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 to archaea’s Mitochondrial, chloroplast DNA
Similar to bacterial DNA Endosymbiont theory:
Mitochondria WERE bacteriaChloroplasts WERE cyanobacteria Infected or eaten by other speciesEnded up living together inside
Endo-sym-biosis
Cell Biology Techniques Electron microscopy
Observation of cell components Eukaryotic organelles Membranes
UltracentrifugeSeparation 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 bacteriaDNA structureGenetic codeTranscription, translationRestriction enzymesRecombinant DNACloningPCR reactionE. coli has best understood genome