5BY543 History of Microbiology and Prokaryotic Cell Structure PDF

History of Microbiology 5BY543 Dr Yusra Siddiqui [email protected] This Photo by Unknown Author is licensed under CC BY  Spontaneous Generation Debate 1632 - 1723 Anton van Leeuwenhoek’s “Animalcules” (Pronounced Lay-ven-hook)...

History of Microbiology 5BY543 Dr Yusra Siddiqui [email protected] This Photo by Unknown Author is licensed under CC BY  Spontaneous Generation Debate 1632 - 1723 Anton van Leeuwenhoek’s “Animalcules” (Pronounced Lay-ven-hook) As a draper (merchant who sells cloth and dry goods), he used lenses to examine cloth. This probably led to his interest in lens making. He assembled hundreds of microscopes, some of which magnified objects 270 times. As he looked at things with his microscopes, he discovered “micro” organisms - organisms so tiny that they were invisible to the naked eye. He called these tiny living organisms “animalcules”. He first described bacteria, Everett showing how to use the microscope protozoans and many cells of the human body. Why are we interested in studying micro-organisms?  Prokaryotes Cytoskeleton Cellular "scaffolding" or "skeleton" within the cytoplasm. Major advance in prokaryotic cell biology in the last decade has been discovery of the prokaryotic cytoskeleton. Up until recently, thought to be a feature only of eukaryotic cells. From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Prokaryotic Cell: M. Ruiz Prokaryotes Plasma Membrane Separates the cell from its environment. Phospholipid molecules oriented so that hydrophilic water-loving heads directed outward and hydrophobic water-hating tails directed inward. Proteins embedded in two layers of lipids (lipid bilayer). Membrane is semi-permeable. Q: What does that mean? Image: Cell Membrane diagram, Dhatfield  Prokaryotes – Plasma Membrane as a Barrier Osmosis Is the diffusion of water across a semi-permeable membrane. Environment surrounding cells may contain amounts of dissolved substances (solutes) that are… - equal to Plasma membrane - less than - greater than CELL Liquid …those found within the cell. Liquid environment environment inside the cell. outside the cell. From the Virtual Microbiology Classroom on ScienceProfOnline.com Images: Osmosis animation; Osmosis with RBCs, M. Ruiz  Prokaryotes – Plasma Membrane as a Barrier Tonicity and Osmosis isotonic: equal concentration of a solute inside and outside of cell. hypertonic: a higher concentration of solute. hypotonic: a lower concentration of solute. REVIEW! Water will always move How Osmosis Works animation toward a hypertonic Diffusion, Osmosis & Active Transport Lecture Main Page of the environment!! Virtual Cell Biology Classroom on the Science Prof Online website From the Virtual Microbiology Classroom on ScienceProfOnline.com Images: Osmosis animation; Osmosis with RBCs, M. Ruiz Image:Water droplet blue bg05.jpg Cells & Water: Osmotic Pressure H2O important reactant in many metabolic reactions. Most cells die in absence of water. Cell walls of bacteria and plants prevent them from exploding in a hypotonic environment, but most bacteria are vulnerable in hypertonic environments. Many bacteria can be plasmolyzed by high concentrations of solutes. You salty perspiration protects you from bacteria that cannot handle the high sodium chloride concentration. The water moves out of the bacterium and it dies of ‘hyperosmostic shock’ Q: Why can you (desiccation). keep honey on the cupboard for months, even years, without it spoiling? Images: Water drop; Sweat on face of runner; Staphylococcus, T. Port; Cells, full of water versus plasmolyzed, Mnolf, Wiki From the Virtual Microbiology Classroom on ScienceProfOnline.com Plasma Membrane as a Barrier ACTIVE TRANSPORT How most molecules move across the plasma membrane. Analogous to a pump moving water uphill. Types of active transport are classified by type of energy used to drive molecules across membranes. ATP Driven Active Transport Energy from adenosine triphosphate (ATP) drives substances across the plasma membrane with the aid of carrier molecules. From the Virtual Microbiology Classroom on ScienceProfOnline.com  Prokaryotes - Cell Wall From the peptidoglycan inwards all bacteria are very similar. Going further out, the bacterial world divides into two major classes (plus a couple of odd types). These are: Gram-positive Gram-negative Images: Staph, Gram Stain, SPO Microbiology From the Virtual Microbiology Classroom on ScienceProfOnline.com Images, T. Port; E coli, Y tambe  Bacterial Cell Wall Peptidoglycan is a huge polymer of interlocking chains of alternating monomers. Provides rigid support while freely permeable to solutes. Backbone of peptidoglycan molecule composed of two amino sugar derivatives of glucose. The “glycan” part of peptidoglycan: - N-acetylglucosamine (NAG) - N-acetlymuramic acid (NAM) NAG / NAM strands are connected by interlocking peptide bridges. The “peptid” part of peptidoglycan. Image: Bonding structure peptidoglycan, From the Virtual Microbiology Classroom on ScienceProfOnline.com Mouagip; Other Image Source Unknown  Prokaryotes - Cell Wall Gram-Positive & Gram-Negative From the Virtual Microbiology Classroom on ScienceProfOnline.com Images: Sources Unknown  Prokaryotes - Cell Wall Gram-Positive & Gram-Negative FYI: The bacterial plasma membrane and cell wall together are called the cell envelope. Image: Gram-positive cell wall schematic, Wiki; From the Virtual Microbiology Classroom on ScienceProfOnline.com Gram-negative cell wall schematic, Jeff Dahl  Q: Why are these differences in bacterial cell wall structure so important? Image: Lipopolysaccharide, Wiki; Gram+ and Gram- cell wall diagram, From the Virtual Microbiology Classroom on ScienceProfOnline.com source unknown; ; Gram-negative cell wall schematic, Jeff Dahl  Prokaryotes - Glycocalyx Some bacteria have an additional layer outside of the cell wall called the glycocalyx. This additional layer can come in one of two forms: 1. Slime Layer - Glycoproteins loosely associated with the cell wall. - Slime layer causes bacteria to adhere to solid surfaces and helps prevent the cell from drying out. - Streptococcus The slime layer of Gram+ Streptococcus mutans allows it to accumulate on tooth enamel (yuck mouth and one of the causes of cavities). Mannitol Salt Other bacteria in the mouth become trapped in the slime and form a biofilm & eventually a buildup of plaque. Images: Slime layer, Encyclopedia Britannica; Biofilm, PHIL # 11706; Dirty From the Virtual Microbiology Classroom on ScienceProfOnline.com toilet, T. Port Sweat on face; Staphylococcus & Mannitol Salt agar, T. Port  Prokaryotes - Glycocalyx 2. Capsule Polysaccharides firmly attached to the cell wall. Capsules adhere to solid surfaces and to nutrients in the environment. Adhesive power of capsules is a major factor in the initiation of some bacterial diseases. Capsule also protect bacteria from being phagocytized by cells of the hosts immune system. From the Virtual Microbiology Classroom on ScienceProfOnline.com Image: Prokaryotic Cell Diagram: M. Ruiz, Other Images Unknown Source  Prokaryotes - Endospores Dormant, tough, non-reproductive structure produced by small number of bacteria. Resistant to radiation, desiccation, lysozyme, temperature, starvation, and chemical disinfectants. Endospores are commonly found in soil and water, where they may survive for very long An endospore stained bacterial smear of periods of time. Bacillus subtilis showing endospores as green and vegetative cells as red. Q: How and why do endospores form? Watch the animated lesson “Bacterial Spore Formation” to find out. Link also provides quiz questions to test your understanding of the material. Q: What are the two endospore producing bacterial genera that were introduced in our History of Microbiology lecture? Image: Bacillus subtilis, SPO Science Image Library, Endospore From the Virtual Microbiology Classroom on ScienceProfOnline.com stain from Dr. Ronald E. Hurlbert, Microbiology 101 lab manual Prokaryotes – Surface Appendages Some prokaryotes have distinct appendages that allow them to move about or adhere to solid surfaces. Consist of delicate stands of proteins. flagella: Long, thin extensions that allow some bacteria to move about freely in aqueous environments. (singular: flagellum) axial filament (endoflagella): Wind around bacteria, causing movement in waves.  Prokaryotes – Surface Appendages fimbriae: Most Gram-negative bacteria have these short, fine appendages surrounding the cell. Gram+ bacteria don’t have. No role in motility. Help bacteria adhere to solid surfaces. Major factor in virulence. (singular: fimbria) pili:Tubes that are longer than fimbriae, usually shorter than flagella. Use for movement, like grappling hooks, and also use conjugation pili to transfer plasmids. (singular = pilus) From the Virtual Microbiology Classroom on ScienceProfOnline.com Images: E. coli fimbriae, Manu Forero; Bacterial conjugation, Adenosine Prokaryotes – Cell Shapes Most bacteria are classifies according to shape: 1. bacillus (pl. bacilli) = rod-shaped 2. coccus (pl. cocci … sounds like cox-eye) = spherical 3. spiral shaped a. spirillum (pl. spirilla) = spiral with rigid cell wall, flagella b. spirochete (pl. spirochetes) = spiral with flexible cell wall, axial filament There are many more shapes beyond these basic ones. A few examples: – Coccobacilli = elongated coccal form – Filamentous = bacilli that occur in long threads – Vibrios = short, slightly curved rods – Fusiform = bacilli with tapered ends Prokaryotes – Arrangements of Cells Bacteria sometimes occur in groups, rather than singly. bacilli divide along a single axis, seen in pairs or chains. cocci divide on one or more planes, producing cells in: - pairs (diplococci) - chains (streptococci) - packets (sarcinae) - clusters (staphylococci). Size, shape and arrangement of cells often first clues in identification of a bacterium. Many “look-alikes”, so shape and arrangement not enough for id of genus and species.  Activity: Identify Each Type of A Cell Shape B & Arrangement C D  What is next? Different techniques used in microbiology to look at microbes: - Microscopy - Culturing - Serology - Molecular biology