Microbiology (Ammara)

• Microbiology


  The study of microscopic organisms
• Microbes


  Microscopic organisms
• Fields of research in microbiology


  • Medical microbiology
  • Systematics
  • Phylogeny
  • Taxonomy
• Medical microbiologists

  Study the role of microbes in health and disease
• United States Surgeon General, Dr. William H. Stewart (1965-1969): '"It is time to close the book on infectious diseases, and declare the war against pestilence won."'
• Microbes have shaped the atmosphere, geology and energy cycles on Earth
• Humans were unaware of the existence of microbes until the 1600s
• The human body has ten times as many microbes as human cells
• What we eat can have an impact on our microbiome
• Caution is needed on the emphasis being placed on the human microbiome, as association does not imply causation
• We have not identified all possible microbes
• Last universal common ancestor (LUCA)

  Common ancestral cell from which all cells descended
• The atmosphere was anoxic until ~2 billion years ago
• Metabolism was exclusively anaerobic until evolution of oxygen-producing phototrophs
• Life was exclusively microbial until ~1 billion years ago
• Three domains of life

  • Archaea
  • Bacteria
  • Eukarya
• Archaea are more closely related to Eukarya than Bacteria
• Eukaryotes

  Have a true nucleus, are typically >10 μm, are diploid, and reproduce sexually
• Prokaryotes

  Lack a true nucleus, are typically 1-5 μm, are haploid, and reproduce asexually
• Eukaryotes and prokaryotes evolved through endosymbiosis
• Microbiology

  The study of long bacterial names which are impossible to pronounce
• Systematics

  The study of diversity of organisms and their relationships
• Phylogeny

  The evolutionary history of an organism
• Taxonomy

  The science in which organisms are characterised, named and classified according to several defined criteria
• Genus and Species

  The levels of classification we usually deal with
• Taxonomic hierarchy of Ureaplasma spp.

  • Kingdom: Eubacteria
  • Phylum: Firmicutes/Proteobacteria
  • Class: Mollicutes/Gammaproteobacteria
  • Order: Mycoplasmatales/Enterobacteriales
  • Family: Mycoplasmataceae/Enterobacteriaceae
  • Genus: Ureaplasma
  • Species: Ureaplasma urealyticum/Escherichia coli
• Species names include the genus and species, and are always written in italics
• Defining a bacterial species

  Difficult, as bacteria reproduce by binary fission and can transfer genes via horizontal gene transfer
• Phenotypic traits

  Characteristics like Gram staining, cell shape, motility, and biochemical properties, which are the basis for much microbiological diagnosis
• Genotypic traits

  Characteristics based on the organism's DNA, such as the gene encoding ribosomal RNA
• Polyphasic approach

  Combines phenotypic, genotypic, and phylogenetic traits to define a bacterial species
• If a new microbe is discovered, it must be isolated, grown in pure culture, and its unique traits determined before it can be established as a new species
• New species must be deposited in a culture collection and described in the scientific literature
• Microbes have both given and taken life throughout history
• Microbiologists of significance

  • Robert Hooke (1635-1703)
  • Antoni van Leeuwenhoek (1632-1723)
  • Louis Pasteur (1822-1895)
  • Robert Koch (1843-1910)
  • Alexander Fleming
  • Barry Marshall
• Prokaryote

  An organism lacking a nucleus and other membrane-bound organelles and usually having its DNA in a single circular molecule
• Bacteria

  • Obtain nutrients faster than competitors
  • Protect itself from toxins - antibiotics
  • Protect itself from predators - amoeba/bacteriophage/immune cells
  • Must have the ability to do all the above, but acting as a single cell
• Bacterial cell shapes

  • Spirullium spp.
• Why are we interested in the structure and contents of a bacterium?
• Prokaryote cell structure

  • Complex outer envelope - protects from environmental stresses
  • Compact genome - maximise the production of cells from limited resources
  • Tightly coordinated cell functions - coordinate action enables high reproduction rate