Microbiology

• Antoni van Leeuwenhoek:

  • Began making and using simple microscopes
  • Often made a new microscope for each specimen
  • Examined water and visualized tiny animals, fungi, algae, and single-celled protozoa known as "animalcules"
  • By the end of the 19th century, these organisms were called microorganisms, now also known as microbes
• Classifications of Microbes:

  • Carolus Linnaeus developed a taxonomic system for naming plants and animals and grouping similar organisms together
  • Leeuwenhoek's microorganisms are grouped into six categories: Bacteria, Archaea, Fungi, Protozoa, Algae, and Small multicellular animals
• Bacteria and Archaea:

  • Prokaryotic organisms that lack nuclei and are much smaller than eukaryotes
  • Found everywhere there is sufficient moisture; some have been isolated from extreme environments
  • Reproduce asexually
  • Bacterial cell walls contain peptidoglycan; some lack cell walls
  • Archaeal cell walls are composed of polymers other than peptidoglycan
• Fungi:

  • Eukaryotic organisms with membrane-bound nuclei that obtain food from other organisms
  • Possess cell walls
  • Include molds (multicellular, grow as long filaments, reproduce by sexual and asexual spores) and yeasts (unicellular, reproduce asexually by budding, some produce sexual spores)
• Protozoa:

  • Single-celled eukaryotes similar to animals in nutrient needs and cellular structure
  • Live freely in water; some live in animal hosts
  • Capable of asexual and sexual reproduction
  • Most are capable of locomotion by pseudopods, cilia, or flagella
• Algae:

  • Unicellular or multicellular organisms that are photosynthetic
  • Have simple reproductive structures
  • Categorized based on pigmentation and composition of cell wall
  • Scientists and manufacturers use many algae-derived products
• Debate over Spontaneous Generation:

  • Aristotle proposed spontaneous generation, which was later challenged by Redi's, Needham's, Spallanzani's, and Pasteur's experiments
  • Pasteur's experiments led to the development of pasteurization and the germ theory of disease
• The Golden Age of Microbiology:

  • Six health care practitioners instrumental in changing health care delivery methods: Semmelweis, Lister, Nightingale, Snow, Jenner, and Ehrlich
• The Modern Age of Microbiology:

  • Kluyver and van Niel proposed basic biochemical reactions shared by all living things
  • Microbes used as model systems for biochemical reactions with practical applications in biochemistry, diagnosis of illnesses, treatment of metabolic diseases, drug design, etc.
• Processes of Life include growth, reproduction, responsiveness, and metabolism
• Prokaryotes have flagella types: Monotrichous, Amphitrichous, Peritrichous, and Lophotrichous
• Fimbriae are sticky, bristlelike projections used by bacteria to adhere to one another and to substances in the environment
• Pili are a special type of fimbria, also known as conjugation pili, longer than fimbriae but shorter than flagella, typically one or two per cell, and transfer DNA from one cell to another (conjugation)
• Bacterial cell walls provide structure, shape, protect from osmotic forces, assist in attaching to other cells, resist antimicrobial drugs, and give bacterial cells characteristic shapes
• Two basic types of bacterial cell walls are Gram-positive and Gram-negative
• Gram-positive bacterial cell walls have a relatively thick layer of peptidoglycan, unique polyalcohols called teichoic acids, and appear purple following Gram staining
• Bacteria without cell walls lack cell walls, are often mistaken for viruses due to small size and lack of cell wall, but have other features of prokaryotic cells like ribosomes
• Bacterial cytoplasmic membranes are composed of a phospholipid bilayer, control passage of substances into and out of the cell, store energy, harvest light energy in photosynthetic bacteria, and are selectively permeable
• Passive transport processes include diffusion, facilitated diffusion, and osmosis
• Active transport processes in prokaryotic cytoplasmic membranes include active transport and group translocation where substances are chemically modified during transport
• E. coli grown in a hypertonic solution turns on a gene to synthesize a protein that transports potassium into the cell to maintain osmotic balance
• Cytosol is the liquid portion of bacterial cytoplasm containing the cell's DNA in the nucleoid, inclusions may include reserve deposits of chemicals, and endospores are unique structures produced by some bacteria as a defensive strategy against unfavorable conditions
• Nonmembranous organelles in bacteria include ribosomes, sites of protein synthesis, and the cytoskeleton composed of protein fibers playing roles in cell division, shape, DNA segregation, and movement
• External structures of Archaea include glycocalyces that function in biofilm formation, flagella with differences from bacterial flagella, fimbriae, and hami to attach archaea to surfaces
• Most archaea have cell walls without peptidoglycan, containing specialized polysaccharides and proteins, and all archaea have cytoplasmic membranes maintaining electrical and chemical gradients, controlling substance import and export
• All archaea have cytoplasmic membranes that maintain electrical and chemical gradients and control import and export of substances from the cell
• Archaeal cytoplasm is similar to bacterial cytoplasm with 70S ribosomes, fibrous cytoskeleton, and circular DNA
• Eukaryotic cells have cytoplasmic membranes that are fluid mosaics of phospholipids and proteins, containing steroid lipids to maintain fluidity and regions called membrane rafts that localize signaling, protein sorting, and movement
• Eukaryotic cell walls are composed of various polysaccharides like cellulose in plants, chitin in fungi, and a variety of polysaccharides in algae
• Eukaryotic glycocalyces are covalently bound to cytoplasmic membranes, helping anchor animal cells, strengthen cell surfaces, protect against dehydration, and function in cell-to-cell recognition and communication
• Many antimicrobial drugs target bacterial cell walls instead of cytoplasmic membranes because bacterial cell walls have unique structures that can be targeted effectively
• Eukaryotic flagella differ structurally and functionally from prokaryotic flagella, being composed of tubulin microtubules arranged in a shaft that undulates rhythmically and propel cells through their environment
• Eukaryotic cells have nonmembranous organelles like ribosomes larger than prokaryotic ones, a cytoskeleton of tubulin microtubules, actin microfilaments, and intermediate filaments, and centrioles that play a role in mitosis, cytokinesis, and formation of flagella and cilia
• Eukaryotic cells also have membranous organelles like the nucleus containing most of the cell's DNA, the endoplasmic reticulum functioning as a transport system, the Golgi body processing and packaging molecules for export, and mitochondria producing most of the cell's ATP
• Colchicine inhibits microtubule formation, affecting phagocytosis, movement of organelles within the cell, and formation of flagella and cilia because these processes rely on intact microtubules for their function