intro to microbiology- lecture 1

• Microorganisms


  All single-celled microscopic organisms, including viruses
• Microbial cells


  • They are independent entities that carry out their life processes independently of other cells
  • They differ fundamentally from plant and animal cells which cannot live alone in nature and exist only as parts of multicellular structures
• Microbiology


  The study of microorganisms

  
• Microbiology


  • It is about microbial cells and how they work, especially bacteria
  • It is about the diversity and evolution of microbial cells
  • It is about what microorganisms do in the world, in soils, waters, the human body, and in animals and plants
  • Microorganisms affect and support all other forms of life, making microbiology the most fundamental of the biological sciences
• Cell


  The fundamental unit of life, an entity isolated from other cells by a membrane, often with a cell wall outside the membrane
• Properties of all cells

  • Metabolism
  • Growth
  • Evolution
• Properties of some cells

  • Motility
  • Differentiation
  • Communication
• Cells as biochemical catalysts

  Carrying out the chemical reactions that constitute metabolism
• Cells as genetic entities


  Replicating DNA and processing it to form the RNAs and proteins needed for maintenance and growth
• Population


  A group of cells derived from a single parental cell by successive cell divisions
• Habitat


  The immediate environment in which a microbial population lives
• Microbial community


  Populations of cells of different species that interact with each other in a habitat
• The diversity and abundance of microorganisms in microbial communities is controlled by the resources and conditions that prevail in their habitat
• Microbial populations interact with each other in beneficial, neutral, or harmful ways
• Microbial communities


  • Populations of cells of different species living together in an environment
  • Diversity and abundance controlled by resources and conditions in the habitat
• Ecosystem


  All the living organisms, together with the physical and chemical components of their environment
• Microorganisms were the first entities on Earth with the properties of living systems
• Last universal common ancestor (LUCA)


  The common ancestral cell from which all cells have descended
• Microorganisms were the only life on Earth for most of its history
• Major microbial ecosystems


  • Aquatic (oceans, ponds, lakes, streams, ice, hot springs)
  • Terrestrial (surface soils, deep subsurface)
  • Other organisms (plants and animals)
• Microorganisms carrying out metabolic processes remove nutrients from the ecosystem and use them to build new cells, while also excreting waste products back into the environment
• As resources and conditions change in a microbial habitat, cell populations rise and fall, changing the habitat once again
• Estimates of total microbial cell numbers on Earth are on the order of 2.5 * 10^30 cells

  
• Most microbial cells are found in the oceanic and terrestrial subsurface, not on Earth's surface
• Microbiology has greatly advanced human health and welfare by understanding microorganisms as agents of disease, and their role in food, agriculture, producing valuable products, generating energy, and cleaning up the environment
• Control of infectious disease has come from an increased understanding of disease processes, improved sanitary and public health practices, and the use of antimicrobial agents, such as antibiotics
• Microorganisms as Agents of Disease
• The statistics summarized in Figure 1.8 show microbiologists' success in preventing infectious diseases since the beginning of the twentieth century
• At the beginning of the twentieth century, the major causes of death in humans were infectious diseases caused by microorganisms called pathogens
• Today, infectious diseases are much less deadly, at least in developed countries
• Microorganisms can still be a major threat, particularly in developing countries
• Microbial diseases that are still major causes of death in developing countries

  • malaria
  • tuberculosis
  • cholera
  • African sleeping sickness
  • measles
  • pneumonia and other respiratory diseases
  • diarrheal syndromes
• Humans worldwide are under threat from diseases that could emerge suddenly, such as bird or swine flu, or Ebola hemorrhagic fever, which are primarily animal diseases that under certain circumstances can be transmitted to humans and spread quickly through a population
• Humans worldwide are under threat from those who would deploy microbial bioterrorism agents
• Most microorganisms are not harmful to humans, and in fact, most microorganisms are beneficial—and in many cases even essential—to human welfare and the functioning of the planet
• Agriculture benefits from the cycling of nutrients by microorganisms
• Nitrogen fixation by bacteria in legume root nodules

  Atmospheric nitrogen (N2) converted into ammonia (NH3) that the plants use as a nitrogen source for growth
• Sulfur cycling by bacteria

  Oxidizing toxic sulfur species such as hydrogen sulfide (H2S) into sulfate (SO4^2-), which is an essential plant nutrient
• Ruminant animals


  • Have a characteristic digestive vessel called the rumen in which large populations of microorganisms digest and ferment cellulose, the major component of plant cell walls, at neutral pH
• Without these symbiotic microorganisms, cattle and sheep could not thrive on cellulose-rich (but otherwise nutrient-poor) food, such as grass and hay