Introduction to Microorganisms

• Microorganisms are organisms too small to be seen with the naked eye.
• Microbes are small, but there are exceptions like Epulopiscium fishelsoni, which is 600 μm long.
• Microbes have a significant impact.
• 10^9 bacteria are found in one gram of soil.
• 10^12 bacteria are on the skin of a single human.
• Aquatic environments contains 10^4 - 10^7 bacteria per mL in aquatic environments.
• There are ~4-6 x 10^30 bacterial cells on Earth.
• 500 x 10^9 Tons of carbon is sequestered in bacteria.
• Bacteria contain 10 x more nitrogen and phosphorus than plants.
• Microbes operate major biogeochemical processes.
• About 10 trillion harmless or essential symbiotic bacteria colonize the human body.
• Microbes can survive under extreme conditions.
• Bacteria were the first and oldest organisms on Earth, dating back 3.5 billion years.
• Bacteria started the production of oxygen 3 billion years ago.
• Most branches on the Tree of Life are microbial, with >100 known major groups (phyla) of bacteria.

Key Events in Microbiology

• 1665: Robert Hooke publishes Micrographia.
• 1668: Francesco Redi refutes spontaneous generation of maggots.
• 1674-1676: Antonie van Leeuwenhoek discovers "animacules".
• 1765-1776: Lazzaro Spallanzani attacks spontaneous generation.
• 1775: American Revolution begins.
• 1798: Edward Jenner introduces cowpox vaccination for smallpox.
• 1854: John Snow traces cholera source to water.
• 1859: Charles Darwin's Origin of Species.
• 1861: Louis Pasteur disproves spontaneous generation.
• 1876: Robert Koch demonstrates that Bacillus anthracis causes anthrax.
• 1884: Koch's postulates are published.
• 1884: Elie Metchnikoff describes phagocytosis.
• 1884: Autoclaves are developed.
• 1884: Gram stain is developed.
• 1885: Louis Pasteur develops rabies vaccine.
• 1887-1890: Sergei Winogradsky studies sulfur and nitrifying bacteria.
• 1888: Martinus Beijerinck isolates root nodule bacteria.
• 1899: Beijerinck proves virus causes tobacco mosaic disease.
• 1911: Francis Peyton Rous discovers a virus can cause cancer.
• 1915-1917: Félix d'Hérelle and Frederick Twort discover bacterial viruses.
• 1927: Lindbergh's transatlantic flight
• 1928: Frederick Griffith discovers bacterial transformation.
• 1929: Alexander Fleming discovers penicillin
• 1932: Ernst Ruska builds first electron microscope

Microscopy Leads to Discovery

• Antony van Leeuwenhoek (1632-1723) made first observations of microorganisms.
• His microscopes magnified 50-300x.
• Leeuwenhoek described microorganisms as "animalcules".

Disproving Spontaneous Generation

• Spontaneous generation states that living organisms can develop from non-living or decomposing matter.
• Francesco Redi (1626-1697) showed that maggots on decaying meat came from fly eggs.
• Louis Pasteur (1822-1895) performed 'swan-neck flask' experiments.

Pasteur’s Swan Neck Procedure

• Pasteur placed nutrient solution in flasks with long, curved necks.
• The solutions were boiled and left exposed to air.
• No growth of microorganisms was observed.

The Golden Age of Microbiology

• In the late 1800s, Pasteur and others showed that microorganisms, rather than supernatural forces and poisonous vapours, cause disease.
• Robert Koch (1843-1910) established the relationship between Bacillus anthracis and anthrax.
• Koch developed criteria now known as "Koch's postulates" to establish the link between a particular microbe and a particular disease.
• Koch won the Nobel Prize for Medicine in 1905 for showing that Mycobacterium tuberculosis​ caused TB.
• Agar, Petri dishes, nutrient broth and nutrient agar, and methods for isolating microorganisms were also developed during this time.

Molecular Biology Revolution

• Carl Woese (1928-2012) used sequences of ribosomal RNA genes to show that bacteria, archaea and eukarya are evolutionarily distinct
• The polymerase chain reaction (PCR) was invented in mid-1980s by Kary Mullis.
• PCR enabled replication and amplification of minute amounts of DNA, revolutionizing biology.
• DNA sequencing became increasingly available through the 1990s/2000s.
• The first bacterial genome (Haemophilus influenzae) was sequenced in 1995.

Lecture Summary

• Microorganisms are globally important:
  • In biomass.
  • In abundance.
  • In diversity.
  • In influence on nutrient cycling and other processes.
• Most branches on the Tree of Life are occupied by microorganisms.
• Understanding of microbiology has developed in parallel with methodological advances:
  • microscopy
  • agar plates for cultivation
  • PCR
  • genome sequencing