chapter 1

• Microorganisms


  Organisms and acellular entities too small to be clearly seen by the unaided eye, generally <1 mm, some macroscopic, relatively simple in their construction and lack differentiated tissues
• The importance of microorganisms

  • Most populous and diverse group of organisms
  • Found everywhere on the planet
  • Play a major role in recycling essential elements
  • Source of nutrients and some carry out photosynthesis
  • Benefit society by their production of food, beverages, antibiotics, and vitamins
  • Some cause disease in people, plants, or animals
• Prokaryotic cells


  • Lack a true membrane-delimited nucleus, this is not absolute
• Eukaryotic cells


  • Have a membrane-enclosed nucleus, are more complex morphologically, and are usually larger than prokaryotic cells
• Classification schemes


  • Three domain system, based on a comparison of ribosomal RNA genes, divides microorganisms into: Bacteria (true bacteria), Archaea, Eukarya (eukaryotes)
• Evolution of the three domains of life

  Universal phylogenetic tree based on comparisons of small subunit rRNA, aligned rRNA sequences from diverse organisms are compared and differences counted to derive a value of evolutionary distance, relatedness but not time of divergence determined this way
• Last Universal Common Ancestor (LUCA)


  The root or origin of modern life is on bacterial branch but nature still controversial, Archaea and Eukarya evolved independently of Bacteria, Archaea and Eukarya diverged from common ancestry
• Evolution of cellular microbes

  Mutation of genetic material led to selected traits, new genes and genotypes evolved—producing mosaic of genetic information, Bacteria and Archaea increase genetic pool by horizontal gene transfer within the same generation
• Microbial species


  Eukaryotic microbes fit definition of reproducing isolated populations, Bacteria and Archaea do not reproduce sexually and are referred to as strains, a strain consists of descendants of a single, pure microbial culture, may be biovars, morphovars, serovars, and pathovars, binomial nomenclature with genus and species epithet
• Important events in microbiology (1665 to 1911)

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• Important events in microbiology (1900 to 2010)

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• Discovery of microorganisms


  Earliest microscopic observations, Robert Hooke: published drawings of the fungus Mucor in his book, Micrographia, in 1665, Antony van Leeuwenhoek: First person to observe micro-organisms accurately
• The conflict over spontaneous generation

  Idea that living organisms can develop from nonliving or decomposing matter, Francesco Redi discredited spontaneous generation, John Needham's experiment showed broth became cloudy and contained microorganisms, Lazzaro Spallanzani's experiment showed no growth of microorganisms
• Louis Pasteur's 'swan-neck flask' experiments

  Placed nutrient solution in flasks, created flasks with long, curved necks, boiled the solutions, left flasks exposed to air, results: no growth of microorganisms
• Final blow to theory of spontaneous generation


  John Tyndall demonstrated that dust carries microorganisms and if dust was absent, nutrient broths remained sterile, even if directly exposed to air, Ferdinand Cohn showed heat-resistant bacteria could produce endospores
• The role of microorganisms in disease


  Was not immediately obvious, infectious disease believed to be due to supernatural forces or imbalances of 4 bodily-fluid 'humors', establishing connection depended on development of techniques for studying microbes
• Louis Pasteur's contributions


  Demonstrated microorganisms carried out fermentations, helping French wine industry, developed pasteurization to avoid wine spoilage by microbes
• Joseph Lister's contributions


  Provided indirect evidence that microorganisms were the causal agents of disease, developed an antiseptic surgery system to prevent microorganisms from entering wounds, his patients had fewer postoperative infections
• Robert Koch's contributions


  Established the relationship between Bacillus anthracis and anthrax, used criteria developed by his teacher Jacob Henle, these criteria now known as "Koch's postulates" are still used today to establish the link between a particular microorganism and a particular disease
• Koch's postulates and tuberculosis

  The microorganism must be present in every case of the disease but absent from healthy organisms, 2. The suspected microorganisms must be isolated and grown in a pure culture, 3. The same disease must result when the isolated microorganism is inoculated into a healthy host, 4. The same microorganisms must be isolated again from the diseased host
• Limitations of Koch's postulates

  Some organisms cannot be grown in pure culture, using humans in completing the postulates is unethical, molecular and genetic evidence may replace and overcome these limits
• Development of techniques for studying microbial pathogens

  Koch's work led to discovery or development of agar, Petri dishes, nutrient broth and nutrient agar, methods for isolating microorganisms, Charles Chamberland developed porcelain bacterial filters used by Ivanoski and Beijerinck to study tobacco mosaic disease, determined that extracts from diseased plants had infectious agents present which were smaller than bacteria and passed through the filters, infectious agents were eventually shown to be viruses
• Other developments


  Pasteur and Roux discovered that incubation of cultures for long intervals between transfers caused pathogens to lose their ability to cause disease (termed 'attenuation'), Pasteur and his coworkers developed vaccines for chicken cholera, anthrax, and rabies
• Immunological studies


  • Edward Jenner used vaccination procedure to protect against smallpox, Emil von Behring and Shibasaburo Kitasato developed antitoxins for diphtheria, Elie Metchnikoff discovered bacteria-engulfing, phagocytic cells in blood
• Microbial ecology


  Sergei Winogradsky and Martinus Beijerinck studied soil microorganisms and discovered numerous interesting metabolic processes (for example, nitrogen fixation), pioneered the use of enrichment cultures and selective media
• Microbiology has basic and applied aspects

  • Basic aspects are concerned with individual groups of microbes, microbial physiology, genetics, molecular biology, and taxonomy, Applied aspects are concerned with practical problems—disease, water, food, and industrial microbiology
• Molecular and genomic methods

  • Discoveries: Restriction endonucleases (Arber and Smith), First novel recombinant molecule (Jackson, Symons, Berg), DNA sequencing methods (Woese, Sanger), Bioinformatics and genomic sequencing and analysis
• Major fields in microbiology

  • Medical microbiology—diseases of humans and animals, Public health microbiology—control and spread of communicable diseases, Immunology—how the immune system protects a host from pathogens, Microbial ecology is concerned with the relationship of organisms with their environment, Agricultural microbiology is concerned with the impact of microorganisms on food production, Food microbiology—microbes used to make food and beverages as well as spoilage microbes
• More microbiology fields


  • Industrial microbiology—penicillin and other antibiotics, vaccines, steroids, alcohols and other solvents, vitamins, amino acids, enzymes, and biofuels, Microbial physiology studies metabolic pathways of microorganisms, Microbial genetics, molecular biology, and bioinformatics study the nature of genetic information and how it regulates the development and function of cells and organisms, Microbes are a model system of genomics
• Domain Bacteria


  • Usually single-celled, majority have cell wall with peptidoglycan, most lack a membrane-bound nucleus, ubiquitous and some live in extreme environments, cyanobacteria produce significant amounts of oxygen
• Domain Archaea


  • Distinguished from Bacteria by unique rRNA gene sequences, lack peptidoglycan in cell walls, have unique membrane lipids, some have unusual metabolic characteristics, many live in extreme environments