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Introduction to Microbiology

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Last revised: Thursday, January 6, 2000
Reading: Ch. 1 in Prescott et al, Microbiology, 4th Ed.
Note: These notes are provided as a guide to topics the instructor hopes to cover during lecture. Actual coverage will always differ somewhat from what is printed here. These notes are not a substitute for the actual lecture!
Copyright 2000. Thomas M. Terry

Unifying Themes

  1. The invisible world of microbes underlies and shapes what we call the "visible world".
  2. Microbes have extraordinary genetic and metabolic diversity.
  3. Microbial metabolism can create anaerobic environments, and anaerobic microbes can exploit these environments.
  4. Different microbes are adapted to survive and exploit an enormous range of environments, both inanimate and animate.
  5. Among all life forms on earth, microbes have the widest range of genetic and evolutionary diversity.

The Subject Matter of Microbiology

1. What are microbes?

2. The Structure of Microbes

Two basic cell architectures: prokaryotes & eukaryotes
prokaryote and eukaryote organization
Image drawn by Thomas M. Terry for The Biology Place. Used with permission.
  1. Prokaryotes
    • "pro" = before, + "karyos" = nucleus
    • Includes bacteria and cyanobacteria (formerly blue-green algae)
    • Simple architecture not understood until EM technology in 1940's
    • Sample electron micrographs
    • Typical sizes: 1 um diameter
  2. Eukaryotes
    • "eu" = true, + "caryos" = nucleus
    • Typically contain membrane-bounded organelles (e.g. mitochondria, lysosomes, endoplasmic reticulum, Golgi bodies)
    • Typical sizes: anywhere from 5 micrometers (yeast cells) to 50 or 100 micrometers. A few cells (such as bird eggs) are enormous, and some cells (such as animal nerve cells) can attain lengths of many meters, even though small in diameter.
    • Includes protists, fungi, animals and plants.

3. The variety of Bacteria

4. History and Distribution of Bacteria

Where do bacteria come from, and where are they found?
  1. History
    • Earth was formed about 4.5 billion years ago (BYA)
    • Fossil bacteria can be found in the oldest rocks (~ 3.8 billion years old)
    • Early Earth was anaerobic. Cyanobacteria evolved ability to use water as raw material in photosynthesis, produced oxygen gas O2 as waste. This led to buildup of O2 in atmosphere from 0% to 20% around 2 BYA.
    • Eearliest fossil eukaryotes are about 1.5 billion years old, and animals evolved about 0.6 billion BYA.
    • All present-day life evolved from bacteria.
  2. Distribution
    • Bacteria are the most abundant organisms on earth, found everywhere; air, water, soil, rocks (live bacteria even found in rocks more than a mile below earth's surface)
    • Billions per gram of fertile soil (will measure this in lab)
    • Humans contain 1014 bacterial cells, 1013 human cells; 10% of dry weight of humans is bacterial (mostly in large intestine). Feces is 1/3 bacteria.
    • One of major human problems: getting rid of microbes, or preventing their growth. Practical problem for food, beverage, cosmetic, pharmaceutcals, other industries.
    • Where are microbes not found? Only inside tissues of organisms, kept at bay by defensive mechanisms. Even so, challenges common (cut finger, get infected).

5. What do microbes do?

  1. When food is abundant, microbial "behavior" is very simple: EAT, GROW, AND DIVIDE.
  2. Watch movie showing E. coli growing in time-lapse photography
  3. Table showing rate of growth of different organims

    Organism Time needed to consume body weight
    Human 180 Days
    Pig 20 Days
    Yeast 30 Minutes
    Lactobacillus 10 Minutes
    Micrococcus 3 Minutes

  4. Growth rates can be phenomenally fast: e.g. some bacteria can reproduce every 20 min. under optimal conditions. 24 hours, could have 271 bacteria = 2.4 x 1021. Bacterial cell weighs ca. 10-12 g., so 24 hours growth weighs 2.4 x 1010grams = 2.4 x 107 kg = 26,400 tons.
  5. Physiology: what kinds of foods do they eat? How do they extract energy? Lots of extraordinary tricks: e.g. some bacteria can use up to 150 different chemicals as the ONLY source of carbon. Mothballs, starch, etc. Imagine your life if you could do this!
  6. Bacteria in animal gut are important for animals to digest food. In some animals, bacteria are obligatory, animals cannot survive without them.
  7. Many human foodstuffs are produced by bacteria or fungi: yogurt, cheese, and other sour milk products; saurkraut; beer, wine, and all other alcoholic beverages; vinegar.
  8. Bacteria rarely enjoy continued ample food, so much time spent in dormant or near-dormant states. Bacteria can survive with minimal metabolism in very extreme environments, including antarctic ice, rocks (as far as a mile below earth's surface), boiling sulfur springs, and more.
  9. Bacteria have many sophisticated mechanisms for handling lack of food, including secreting antibiotics and other toxins ("get rid of the competition"), modifying intracellular metabolism, and producing modified structures for dormancy (spores, cysts, endospores).

6. Why is microbiology important?

  1. Disease. Since discovery of infectious microbes, most infectious diseases controlled by sanitation, preventive medicine, and chemotherapy.
  2. Agriculture. microbes vital in processing materials in soil, e.g. nitrogen, sulfur, etc.
  3. Food and drink. Microbial fermentations responsible for all alcoholic beverages, breads, pickles, cheeses, etc. Control of food and drink spoilage is major concern of food industry.
  4. Chemical products. Microbes have incredible variety of metabolic tricks; can be used to produce acetone and other commercial solvents, pharmaceuticals, antibiotics, preservatives, etc.
  5. Basic research. Microbes grow fast, produce enormous # of offspring. Easy to find events that occur only 1 in a billion times if have 100 billion bacteria in test tube. Crucial to modern biology.
  6. Biotechnology. E.g. genetic engineering, ability to move genes freely from one organism to another, select genes of interest and amplify their expression. Bacteria are natural hosts for such activities.

7. How did microbiology become a science? Major historical figures

Spontaneous Generation controversy.

Microbes cause Disease!

Late 1800's: "Golden Age" of Microbiology.

Microbes transform organic and inorganic matter

Recent Developments

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