Microorganisms Overview

Microorganisms

• Tiny living things that can only be seen with a microscope.
• Found everywhere on Earth.

Cellular vs. Acellular Microorganisms

• Cellular microorganisms have cells, while acellular microorganisms do not.
• Examples of cellular microorganisms include bacteria, fungi, and protists.
• Examples of acellular microorganisms include viruses and prions.

Cellular Microorganisms

• Divided into several groups:
  • Fungi: Yeasts and molds
  • Protists: Algae and protozoa
  • Bacteria: Escherichia coli and other bacteria

Acellular Microorganisms

• Not made up of cells.
• Smaller and simpler than cellular microorganisms.
• Examples:
  • Viruses: Composed of protein and nucleic acid
  • Viroids: Composed of RNA
  • Satellites: Composed of nucleic acid
  • Prions: Composed of protein

The Three Domains of Life

• Microorganisms are classified into three domains: Bacteria, Archaea, and Eukarya.
  • Bacteria and Archaea are prokaryotic.
  • Eukarya are eukaryotic.

Domain Bacteria

• Single-celled organisms with cell walls containing peptidoglycan.
• Found in a variety of environments, including soil, water, and the human body.
• Most bacteria are beneficial, but some can cause disease.

Domain Archaea

• Single-celled organisms that are similar to bacteria in appearance but have distinct genetic and biochemical characteristics.
• Many archaea are found in extreme environments, such as hot springs and salt lakes.

Domain Eukarya

• Include all eukaryotic organisms, such as protists, fungi, animals, and plants.
• Protists are generally unicellular and larger than bacteria and archaea.

The Importance of Microorganisms

• Essential roles in the biosphere:
  • Breaking down dead organic matter
  • Producing food
  • Maintaining human health

The Impact of Microorganisms on Human Health

• Many microorganisms are beneficial, but some can cause disease:
  • Diseases caused by microorganisms include the plague, tuberculosis, and influenza.

The Early History of Microbiology

• The first microscopic observations of microorganisms were made by Robert Hooke in 1665.
• Antony van Leeuwenhoek later made detailed observations of bacteria and protists.

Spontaneous Generation

• The theory of spontaneous generation proposed that living organisms could arise from nonliving matter.
• Francesco Redi's experiments disproved this theory for larger organisms.

The Golden Age of Microbiology

• A period of rapid advancement in the field of microbiology.
• Louis Pasteur and Robert Koch made significant contributions to our understanding of microorganisms and their role in disease.

Culture-Based Methods

• Used to isolate and study microorganisms in the laboratory.
• Involve growing microorganisms on nutrient-rich media.

The Debate Over Spontaneous Generation

• John Needham and Lazzaro Spallanzani conducted experiments to investigate spontaneous generation.
  • Needham's experiments seemed to support the theory, while Spallanzani's experiments challenged it.

The Contributions of Schwann, Schroder, and von Dusch

• Theodore Schwann, Georg Friedrich Schroder, and Theodor von Dusch conducted experiments that further challenged the theory of spontaneous generation.
• They demonstrated that microbial growth could not occur in sterile nutrient solutions unless air was allowed to enter.

Felix Pouchet and the Controversy

• Felix Pouchet claimed to have proven that microbial growth could occur without air contamination.
• This reignited the debate over spontaneous generation.

Louis Pasteur's Experiments

• Conducted definitive experiments that disproved the theory of spontaneous generation.
• He used swan-neck flasks to prevent air contamination while allowing air to enter.

The Importance of Pasteurization

• Pasteur's work led to the development of pasteurization, a process that is used to kill harmful microorganisms in food and beverages.

The Germ Theory of Disease

• States that microorganisms are the cause of many infectious diseases.
• Robert Koch developed Koch's postulates, a set of criteria for establishing a causal link between a microorganism and a disease.

Early Evidence for the Germ Theory

• Agostino Bassi demonstrated that a silk-worm disease was caused by a fungal infection.
• M.J. Berkeley proved that the great potato blight of Ireland was caused by a water mold.

Pasteur's Contributions to Microbiology

• Louis Pasteur made significant contributions to microbiology, including:
  • disproving the theory of spontaneous generation
  • developing the pasteurization process
  • investigating the role of microorganisms in fermentation and disease.

The Role of Microorganisms in Fermentation

• Pasteur discovered that specific types of microorganisms were responsible for different types of fermentation, such as the production of alcohol and acid in wine.

Lister's Contributions to Antiseptic Surgery

• Joseph Lister developed a system of antiseptic surgery to prevent microorganisms from entering wounds, thereby reducing the risk of infection.

The Importance of Pure Cultures

• To study microorganisms, it is essential to isolate them in pure culture, free from other microorganisms.

Culture Media

• Used to grow microorganisms in the laboratory.
• Provide nutrients and a suitable environment for growth.

The Role of Gelatin and Agar

• Gelatin and agar are used to solidify culture media.
  • Gelatin is susceptible to digestion by some microorganisms, while agar is more resistant.

The Petri Dish

• A shallow, circular dish with a lid, used for culturing microorganisms on solid media.

The Challenges of Isolating Microorganisms

• Some microorganisms, such as Mycobacterium leprae, cannot be isolated in pure culture due to technical difficulties or ethical concerns.

Molecular Methods in Microbiology

• Molecular methods, such as DNA sequencing and gene editing, can be used to study microorganisms even when they cannot be isolated in pure culture.

Explore the fascinating world of microorganisms in this quiz. Learn about cellular versus acellular organisms, their classifications, and the three domains of life. Test your knowledge about bacteria, fungi, viruses, and more!