week 1

• Microbe


  A living organism that requires a microscope to be seen
• Microbial cells range in size from millimeters (mm) down to 0.2 micrometer (µm), and viruses may be tenfold smaller
• Examples of microbes


  • Bacteria
  • Viruses
  • Fungi
  • Archaea
• Some species of protists, such as giant amoebas, grow to sizes large enough to see with the unaided eye
• Many microbes form complex multicellular assemblages, such as mushrooms, kelps, and biofilms
• In these microbial communities, cells are differentiated into distinct types that complement each other's functions, as in multicellular organisms
• Virus


  A non-cellular particle containing genetic material that takes over the metabolism of a cell to generate more virus particles
• Some viruses consist of only a short chromosome packed in protein
• Microbes


  Include prokaryotes (cells lacking a nucleus, including bacteria and archaea) and some classes of eukaryotes (cells with a nucleus), such as algae, fungi, and protists
• The bacteria, archaea, and eukaryotes known as the three "domains" evolved from a common ancestral cell
• The formal names of the three domains are Bacteria, Archaea, and Eukarya
• Genome


  The total genetic information contained in an organism's chromosomal DNA
• The genes in a microbe's genome and the sequence of DNA tell us a lot about how that microbe grows and associates with other species
• By comparing DNA sequences of different microbes, we can figure out how closely related they are and how they evolved
• Fred Sanger devised the method of DNA sequence analysis used to sequence the first genomes
• Today we sequence new bacterial genomes daily for a number of different uses
• Metagenome


  The collection of sequences taken directly from the environment
• Some organisms exist in both microbial and macroscopic forms
• A microbial community may include both microbial and macroscopic species
• Microbial capabilities are defined by their genome sequences
• Yeast and bacteria were used to make bread, cheese, and alcoholic drinks
• In the seventeenth and eighteenth centuries, microscopists formulated key concepts about microbes
• In the nineteenth century, there was the "golden age" of microbiology, with the establishment of fundamental principles of disease pathology and microbial ecology that are still in use today
• Microbiology has provided the foundation for modern biology, in which genetics and molecular biology provide powerful tools for scientists to manipulate microorganisms for medicine, research, and industry
• Bubonic plague (Yersinia pestis) and AIDS (Human immunodeficiency virus) have profoundly affected human history
• The plague-induced population decline enabled the social transformation that led to the Renaissance, a period of unprecedented cultural advancement
• The United Nations estimates that 35 million people are living with HIV infection today, and this year 1.2 million will die of AIDS
• Robert Hooke (1635–1703) was the first microscopist to publish a systematic study of the world as seen under a microscope and built the first compound microscope
• Antonie van Leeuwenhoek (1632–1723) observed bacteria with a single lens, becoming the first individual to observe single-celled microbes
• Spontaneous generation


  The concept that living creatures such as maggots could arise spontaneously, without parental organisms
• Lazzaro Spallanzani (1729–1799) showed that microbes arise from preexisting microbes and demonstrated that heat sterilization can prevent microbial growth
• Louis Pasteur (1822–1895) discovered the microbial basis of fermentation and showed that providing oxygen does not enable spontaneous generation
• Pasteur's contributions to the science of microbiology and immunology earned him lasting fame
• Koch's postulates


  The first scientific basis for determining that a specific microbe causes a disease, devised by the German physician Robert Koch (1843–1910)
• Koch's curiosity about the natural world led him to develop principles and methods crucial to microbial investigation, including the pure-culture technique and the famous Koch's postulates for identifying the causative agent of a disease
• Koch's postulates


  1. The microbe is found in all cases of the disease but is absent from healthy individuals

  2. The microbe is isolated from the diseased host and grown in pure culture

  3. When the microbe is introduced into a healthy, susceptible host (or animal model), the host shows the same disease

  4. The same strain of microbe is obtained from the newly diseased host. When cultured, the strain shows the same characteristics as before
• Less than 0.1% of all microbial species can be cultured in the laboratory
• Among the first to study microbes in natural habitats was the Russian scientist Sergei Winogradsky (1856–1953)
• Winogradsky waded through marshes to discover microbes with metabolisms quite alien from human digestion
• The bacteria that Winogradsky isolated can grow only on inorganic minerals