Prescott's Microbiology: Members of the Microbial World

Prescott's Microbiology - Twelfth Edition

• The book is Prescott's Microbiology, 12th edition, by Joanne Willey, Kathleen Sandman, and Dorothy Wood.
• It's published by McGraw Hill.

Members of the Microbial World

• Microorganisms are organisms too small to be seen by the naked eye.
• Most are less than 1mm but some are macroscopic, like bread mold.
• They have a simple structure and lack differentiated tissues.

Divisions and Types of Microbes

• Microbes can be classified as cellular or acellular.
• Cellular microbes include Fungi (e.g., yeasts, molds, slime molds), Protists (e.g., algae, protozoa, slime molds), Bacteria (e.g., Escherichia coli), and Archaea (e.g., Methanogens).
• Acellular microbes include Viruses, Viroids, Satellites, and Prions
• Viruses are composed of protein and nucleic acid.
• Viroids are composed of RNA.
• Satellites are composed of nucleic acid enclosed in a protein shell.
• Prions are composed of protein.

Diversity of Microorganisms

• The number of microbial cells on Earth is greater than the number of stars in the known universe (10^30).
• Microbes are found in various environments, including the atmosphere, soil, sediments, oceans, and the human gut.
• These environments contain vastly different quantities of microbes.

Classification Schemes

• Classifications are based on comparisons of ribosomal RNA genes.
• Three main domains exist: Bacteria, Archaea, and Eukarya
• Prokaryotic cells (bacteria and archaea) do not have a nucleus.
• Eukaryotic cells have a membrane-enclosed nucleus.
• Eukaryotes are generally larger and more morphologically complex than prokaryotes.

Domain Bacteria

• Bacteria are usually single-celled organisms.
• They typically have a cell wall containing peptidoglycan
• Most lack a membrane-bound nucleus.
• Bacteria live in many environments, including the human body.
• A significant portion have either disease causing potential or are helpful to health.

Domain Archaea

• Archaea are distinguished from bacteria by unique rRNA sequences, and have unique membrane lipids and metabolic characteristics.
• Many archaea live in extreme environments.
• Archaea do not cause disease in humans.

Domain Eukarya

• Eukarya are typically larger than bacteria and archaea.
• Protists are mostly unicellular organisms, like the protozoa with animal-like metabolism, or the algae which are photosynthetic
• Fungi are either unicellular (e.g., yeasts) or multicellular (e.g., molds, mushrooms).

Microbial Evolution

• Life on Earth originated 3.5 to 3.8 billion years ago.
• Evidence for early life comes from fossils, molecular fossils, and hopanes.

Relationships of DNA/RNA/Protein in Cells

• Proteins are catalysts (enzymes) and structural components.
• DNA stores hereditary information.
• RNA acts as a messenger, carrying instructions for protein synthesis from DNA.

Which Came First?

• Proteins need RNA and other proteins to be made.
• DNA is for storage only, not cellular function
• RNA needs DNA and proteins to work.
• It appears they rely on one another for function. One molecule was likely first, possibly RNA.

Earliest Molecules-RNA

• The original molecule must have been able to store, copy, and express genetic information.
• Ribozymes are catalytic RNA molecules that may have formed peptide bonds.
• Early cells may have been RNA enclosed in vesicles.

RNA World

• A lipid membrane formed around RNA.
• Lipids spontaneously form vesicles.
• A hypothesis proposes that most cellular RNA in modern cells is associated with the ribosome and involved in protein synthesis

Earliest Metabolism

• Early Earth was hot and oxygen-free.
• Early cells needed to use inorganic molecules for energy.
• Photosynthesis emerged early on, with stromatolites as evidence.

Endosymbiotic Hypothesis

• Mitochondria, chloroplasts, and hydrogenosomes arose through endosymbiosis.
• Their DNA and ribosomes are similar in sequence to bacteria.

The Endosymbiotic Theory

• The theory describes the evolution of eukaryotic cells through the incorporation of prokaryotic cells.
• Mitochondria originated from proteobacteria, and chloroplasts from cyanobacteria.

Evolution of Cellular Microbes

• Mutation in genetic material led to selected traits.
• Bacteria and archaea increased their gene pool through horizontal gene transfer.
• Eukaryotes increased diversity through sexual reproduction

Phyletic Classification Systems

• Phyletic classification systems compare organisms based on their evolutionary relationships.
• Microbial phylogeny compares cell wall structure, biomolecules, and nucleotide sequences.
• Phylogenetic trees show evolutionary relationships.

Phyletic Classification Systems 2

• Universal phylogenetic trees are based on comparisons of small subunit rRNA.
• Aligned rRNA sequences from diverse organisms are compared to determine evolutionary distance.
• This indicates relatedness, but does not show the time of divergence.

Building a Phylogenetic Tree – Distance

• The distance-based approach uses sequence differences to determine evolutionary distance.
• More sequence differences correlate with a greater evolutionary distance.
• An algorithm then generates a phylogenetic tree.

Building a Phylogenetic Tree – Character

• The character-based approach constructs more robust phylogenetic trees by accounting for various characters in organisms
• It needs assumptions about the pathway of evolution and rigorous checking for accuracy

Microbial Taxonomy

• Taxonomy is the science of classifying living organisms.
• This includes classification, nomenclature (binomial nomenclature), and identification
• Strains are descendants of a pure microbial culture; can differ biochemically, morphologically, and pathogenically.

Microbiology-Origins

• Microbiology studies microorganisms
• It uses tools such as microscopes, culture techniques(including isolated strains) , and molecular genetics/genomics.

Discovery of Microorganisms

• Francesco Stelluti observed bees and weevils.
• Robert Hooke drew the fungus Mucor.
• Antony van Leeuwenhoek was the first to accurately observe microorganisms.

The Conflict Over Spontaneous Generation

• Spontaneous generation was the idea that living organisms arise from non-living matter.
• Francesco Redi disproved it by showing maggots came from fly eggs.

Louis Pasteur

• 'Swan-neck flask' experiments disproved spontaneous generation by showing that microorganisms in the air were responsible for contamination, not spontaneous generation.

Swan-Necked Flask Experiments of Pasteur

• Microbes were destroyed by applying vigorous heat.
• When the neck of a flask was broken, the broth became contaminated.
• When the neck of a flask was left intact, the broth stayed sterile.

Final Blow to Theory of Spontaneous Generation

• John Tyndall showed dust carries microorganisms.
• Ferdinand Cohn demonstrated exceptionally heat-resistant bacteria can form endospores.

Early Evidence for the Relationship Between Microorganisms and Disease

• Agostino Bassi showed a silkworm fungus disease.
• M.J. Berkeley demonstrated the potato blight.
• Heinrich de Bary showed fungi caused crop diseases.

Louis Pasteur (1822 to 1895)

• Demonstrated that microorganisms carry out fermentation.
• Developed pasteurization to prevent wine spoilage.

Joseph Lister (1827 to 1912)

• Provided support that microorganisms cause disease.
• Developed antiseptic surgery to prevent wound infections.

Final Proof

• Robert Koch established the link between Bacillus anthracis and anthrax.
• Koch demonstrated that Mycobacterium tuberculosis causes tuberculosis.
• Koch's postulates are still used to link microorganisms and diseases today

Koch's Postulates and Tuberculosis

• Koch's postulates are a set of criteria used to demonstrate that a particular microorganism is the cause of a specific disease.
• These postulates are applicable in determining if a specific microbe directly causes a disease, as well as identifying that microbe

Limitations of Koch's Postulates

• Some organisms can't be cultured in pure form due to reliance on host cells.
• Animal models might not accurately reflect human response to pathogen, and using humans is ethically problematic.

The Development of Techniques for Studying Microbial Pathogens

• Koch's work led to the development of nutrient broth and agar, enabling microbiological isolation.
• Chamberland developed porcelain bacterial filters to study pathogens.

Development of Vaccines

• Pasteur and Roux discovered that longer incubation intervals during pathogen culture led to attenuated strains.
• These attenuated cultures could be used as vaccines against diseases like chicken cholera, anthrax, and rabies.

Immunological Studies

• Jenner used vaccination against smallpox
• von Behring and Kitasato developed antitoxins (antibodies) for diphtheria.
• Metchnikoff identified phagocytic cells as part of the immune system.

Microbial Ecology

• Winogradsky studied soil microorganisms and their metabolic processes, including nitrogen fixation.
• Beijerinck pioneered enrichment cultures and selective media for microbiology research.

Basic and Applied Aspects of Microbiology

• Basic aspects deal with microbes' individual characteristics, physiology, genetics, molecular biology, and taxonomy.
• Applied aspects tackle practical uses of microbes in areas such as disease, water, food, and industrial processes.

Major Fields in Microbiology

• Medical microbiology examines human and animal diseases, like COVID-19.
• Public health microbiology focuses on communicable disease control.
• Immunology studies how the immune system combats pathogens.
• Microbial ecology analyzes the interrelationships between microbes and their environments.
• Agricultural microbiology investigates the effects of microbes on agriculture.
• Food microbiology studies microbes' involvement in food production and spoilage.

More Microbiology Fields

• Industrial microbiology utilizes microbes in producing useful products like antibiotics, vaccines, steroids, solvents, vitamins, amino acids, enzymes, and biofuels.
• Microbial physiology studies the metabolic processes of microorganisms
• Microbial genetics, molecular biology and bioinformatics focuses on the nature of genetic information, and how genetic information regulates cellular and organismal function

Explore the fascinating world of microorganisms with this quiz from Prescott's Microbiology 12th edition. Learn about the diversity, structure, and classification of various microbes, including cellular organisms like fungi and bacteria, as well as acellular entities like viruses and prions.