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Chapter 6

Chapter 6. Microbial Nutrition and Growth. Growth Requirements. Microbial growth Increase in a population of microbe Result of microbial growth is discrete colony An aggregation of cells arising from single parent cell Reproduction results in growth. Growth Requirements.

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Chapter 6

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  1. Chapter 6 Microbial Nutrition and Growth

  2. Growth Requirements • Microbial growth • Increase in a population of microbe • Result of microbial growth is discrete colony • An aggregation of cells arising from single parent cell • Reproduction results in growth

  3. Growth Requirements • Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures • Most common nutrients contain necessary elements such as carbon, oxygen, nitrogen, and hydrogen • Microbes obtain nutrients from variety of sources

  4. Growth Requirements • Nutrients: Chemical and Energy Requirements • Sources of carbon, energy, and electrons • Two groups of organisms based on source of carbon • Autotrophs • Heterotrophs • Two groups of organisms based on source of energy • Chemotrophs • Phototrophs

  5. Groups of organisms based on carbon and energy source Figure 6.1

  6. Growth Requirements • Nutrients: Chemical and Energy Requirements • Oxygen requirements • Oxygen is essential for obligate aerobes • Oxygen is deadly for obligate anaerobes • How can this be true? • Toxic forms of oxygen are highly reactive and excellent oxidizing agents • Resulting oxidation causes irreparable damage to cells

  7. Growth Requirements • Nutrients: Chemical and Energy Requirements • Oxygen requirements • Four toxic forms of oxygen • Singlet oxygen • Superoxide radicals • Peroxide anion • Hydroxyl radical

  8. Catalase test Figure 6.2

  9. Growth Requirements • Nutrients: Chemical and Energy Requirements • Oxygen requirements • Aerobes • Anaerobes • Facultative anaerobes • Aerotolerant anaerobes • Microaerophiles

  10. Identifying the oxygen requirements of organisms Figure 6.3

  11. Growth Requirements • Nutrients: Chemical and Energy Requirements • Nitrogen requirements • Anabolism often ceases due to insufficient nitrogen • Nitrogen acquired from organic and inorganic nutrients • All cells recycle nitrogen from amino acids and nucleotides • Nitrogen fixation by certain bacteria is essential to life on Earth

  12. Growth Requirements • Nutrients: Chemical and Energy Requirements • Other chemical requirements • Phosphorus • Sulfur • Trace elements • Only required in small amounts • Growth factors • Necessary organic chemicals that cannot be synthesized by certain organisms

  13. Growth Requirements • Physical Requirements • Temperature • Effect of temperature on proteins • Effect of temperature on lipid-containing membranes of cells and organelles • If too low, membranes become rigid and fragile • If too high, membranes become too fluid

  14. Effects of temperature on microbial growth Figure 6.4

  15. Categories of microbes based on temperatures for growth Figure 6.5

  16. An example of a psychrophile Figure 6.6

  17. Growth Requirements • Physical Requirements • pH • Organisms sensitive to changes in acidity • H+ and OH– interfere with H bonding • Neutrophiles grow best in a narrow range around neutral pH • Acidophiles grow best in acidic habitats • Alkalinophiles live in alkaline soils and water

  18. Growth Requirements • Physical Requirements • Physical effects of water • Microbes require water to dissolve enzymes and nutrients • Water is important reactant in many metabolic reactions • Most cells die in absence of water • Some have cell walls that retain water • Endospores and cysts cease most metabolic activity • Two physical effects of water • Osmotic pressure • Hydrostatic pressure

  19. Growth Requirements • Physical Requirements • Physical effects of water • Osmotic pressure • The pressure exerted on a semipermeable membrane by a solution containing solutes that cannot freely cross membrane • Hypotonic solutions have lower solute concentrations • Hypertonic solutions have greater solute concentrations • Restricts organisms to certain environments • Obligate and facultative halophiles

  20. Growth Requirements • Physical Requirements • Physical effects of water • Hydrostatic pressure • Water exerts pressure in proportion to its depth • Barophiles live under extreme pressure • Their membranes and enzymes depend on pressure to maintain their three-dimensional, functional shape

  21. Growth Requirements • Associations and Biofilms • Organisms live in association with different species • Antagonistic relationships • Synergistic relationships • Symbiotic relationships

  22. Growth Requirements • Associations and Biofilms • Biofilms • Complex relationships among numerous microorganisms • Develop an extracellular matrix • Adheres cells to one another • Allows attachment to a substrate • Sequesters nutrients • May protect individuals in the biofilm • Form on surfaces often as a result of quorum sensing • Many microorganisms more harmful as part of a biofilm

  23. Plaque on a human tooth Figure 6.7

  24. Culturing Microorganisms • Inoculum introduced into medium • Environmental specimens • Clinical specimens • Stored specimens • Culture • Act of cultivating microorganisms or the microorganisms that are cultivated

  25. Characteristics of bacterial colonies Figure 6.8

  26. Culturing Microorganisms • Obtaining Pure Cultures • Cultures composed of cells arising from a single progenitor • Progenitor is termed a CFU • Aseptic technique prevents contamination of sterile substances or objects • Two common isolation techniques • Streak plates • Pour plates

  27. The streak-plate method of isolation Figure 6.9

  28. The pour-plate method of isolation Figure 6.10

  29. Culturing Microorganisms • Culture Media • Majority of prokaryotes have not been grown in culture medium • Six types of general culture media • Defined media • Complex media • Selective media • Differential media • Anaerobic media • Transport media

  30. Slant tube containing solid media Figure 6.11

  31. An example of the use of a selective medium Figure 6.12

  32. The use of blood agar as a differential medium Figure 6.13

  33. The use of carbohydrate tubes as differential media Figure 6.14

  34. MacConkey agar as a selective and differential medium Figure 6.15

  35. The GasPak anerobic system Figure 6.16

  36. Culturing Microorganisms • Special Culture Techniques • Techniques developed for culturing microorganisms • Animal and cell culture • Low-oxygen culture • Enrichment culture

  37. A candle jar Figure 6.17

  38. Culturing Microorganisms • Preserving Cultures • Refrigeration • Stores for short periods of time • Deep-freezing • Stores for years • Lyophilization • Stores for decades

  39. Growth of Microbial Populations Animation: Bacterial Growth: Overview

  40. Growth of Microbial Populations Animation: Binary Fission

  41. Binary fission Figure 6.18

  42. A comparison of arithmetic and logarithmic growth Figure 6.19

  43. Growth of Microbial Populations • Generation Time • Time required for a bacterial cell to grow and divide • Dependent on chemical and physical conditions

  44. The growth curves of logarithmic growth Figure 6.20

  45. A typical microbial growth curve Figure 6.21

  46. Growth of Microbial Populations Animation: Bacterial Growth Curve

  47. Growth of Microbial Populations • Measuring Microbial Reproduction • Direct methods • Serial dilution and viable plate counts • Membrane filtration • Most probable number • Microscopic counts • Electronic counters

  48. Serial dilution and viable plate count Figure 6.22

  49. Membrane filtration Figure 6.23

  50. The most probable number method (MPN) Figure 6.24

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