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Microbial Growth

Microbial growth is an important topics in the field of medical microbiology.

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Microbial Growth

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  1. MICROBIAL GROWTH Dr. Md. Abdullah Yusuf Assistant Professor (Microbiology) Email: ayusuf75@yahoo.com Cell no.: +8801817565830

  2. Microbial Growth Objectives • Meaning of growth • The requirements for growth • A. Environmental (Physical) requirements • B. Nutritional requirements • Binary fission and growth curve

  3. Microbial growth • Means orderly increase in all the components of a cell • Indicated by increase in microbial population due to binary fission • Number of progeny increases as per rule of geometric progression e.g- 1 to 2, 2 to 4, 4 to 8, 8 to 16 etc. • Time require to divide one bacterium into 2 is called “generation time or doublung time” • Generally in the range of minutes for ordinary bacteria and in the range of hours for slow growing bacteria

  4. BASIC NUTRITIONAL REQUIREMENTS •    A SOURCE OF ENERGY. This may be light (the sun or lamps) or inorganic substances like sulfur, carbon monoxide or ammonia, or preformed organic matter like sugar, protein, fats etc. Without energy life can not exist and quickly dies or becomes inactive. •    A SOURCE OF NITROGEN. This may be nitrogen gas, ammonia, nitrate/nitrite, or a nitrogenous organic compound like protein or nucleic acid.

  5. Bacterial nutrition • A SOURCE OF WATER. All life requires liquid water in order to grow and reproduce. Some resting stages of cells, like bacterial spores, can exist for long periods without free water, but they do not grow or metabolize. • A SOURCE OF MINERALS LIKE IRON, ZINC, COBALT ETC. These are called TRACE metals that are required by some enzymes to function.

  6. Bacterial nutrition • A SOURCE OF CARBON. This can be carbon dioxide or monoxide, methane, carbon monoxide, or complex organic material • A SOURCE OF OXYGEN. All cells use oxygen in a bound form and many require gaseous oxygen (air), but oxygen is lethal to many microbes. • A SOURCE OF PHOSPHOROUS, SULFUR, MAGNESIUM, POTASSIUM & SODIUM. • A SOURCE OF CALCIUM. Most cells require calcium in significant quantities, but some seem to only need it in trace amounts.

  7. Bacterial nutrition • Many bacteria can synthesize every complex molecule they need from the BASIC MINERALS, but others, said to be FASTIDIOUS, require PREFORMED organic molecules like vitamins, amino acids, nucleic acids, carbohydrates. • In general bacterial pathogens need more PREFORMED ORGANIC MOLECULES than do non-pathogens, but that is not always true.

  8. Other requirements for growth • A. Environmental (Physical) requirements • 1. Temperature and moisture • psychrophilesCold loving. 0 - 15oC. • mesophiles Moderate temperature loving. 10 - 45oC • thermophiles Heat loving. 46 - 64oC. • extreme thermophiles 65 - 110oC. • Have a minimum, optimum, and maximum temperature of growth

  9. I. The requirements for growth, cont. • A. Physical requirements • 2. Osmotic Pressure • Most cells live in isotonic solutions. • Hypertonic solutions dehydrate cells ( Used for food preservation) • Halophile- Salt loving. • Extreme or obligate halophiles require high salt (archaea). • Facultative halophiles can grow in high salt.

  10. I. The requirements for growth, cont. • B. Nutritional (Chemical ) Requirements • 1. Carbon • autotroph -Gets carbon from CO2. • Heterotroph- Gets carbon from organic source. • 2. Nitrogen, sulfur, & phosphorous • Nitrogen for proteins, DNA, RNA, ATP • Sulfur for some amino acids & vitamins • Phosphorous for nucleic acids, ATP, phospholipids

  11. I. The requirements for growth, cont. • B. Chemical requirements • 3. Trace elements: potassium, magnesium, calcium, iron, copper, molybdenum, and zinc. Are needed as cofactors for enzymes. • 4. Oxygen • Both useful and harmful • Useful in respiration • Harmful because is a strong oxidizing agent

  12. I. The requirements for growth, cont. • B. Chemical requirements • 5. pH • Optimum for most bacteria, is pH 6 to pH 8 • Optimum for yeast is about pH 5 • Acidophiles (Lactobacillus) grow at very low pH. • Alkalophiles (Vibrio cholerae) grow at high pH.

  13. The requirements for growth, cont. • B. Chemical requirements • 4. Oxygen. Classification of organisms • obligate aerobe Requires oxygen. • facultative anaerobe Grows with or without oxygen. • obligate anaerobe Grows only in absence of oxygen. • aerotolerant anaerobe Grows in presence of oxygen, but does not use it. • microaerophile Grows in low oxygen concentration and high CO2 tension.

  14. I. The requirements for growth, cont. • Why is oxygen harmful? • It is a strong oxidizing agent. It pulls electrons off other molecules. • What is formed in presence of oxygen? • Singlet oxygen • Superoxide free radical: O2- • Hydrogen peroxide: H202 • Hydroxyl radical: OH-

  15. I. The requirements for growth, cont. • Toxic compounds in turn pull electrons off other molecules, e.g., lipids, proteins, and nucleic acids. • Result: Cell is harmed if it cannot get rid of toxic forms of oxygen. • To get rid of toxic oxygen compounds, cells need: • Superoxide dismutase (SOD) • 02-. + 02-. + 2H+ H202 + 02 • Catalase • 2H202 2H20 + 02

  16. I. The requirements for growth, cont. • B. Chemical requirements, etc. • 6. Organic growth factors may be needed • Vitamins • Amino acids • Purines • Pyrimidines

  17. II. Population growth

  18. II. Population growth, cont. • Steps of binary fission: • 1. Cell elongates, and DNA replicates. • 2. Cell wall and plasma membrane increase in size and form septum. • 3. Cross wall forms around DNA. • 4. Cells separate.

  19. II. Population Growth, cont. • Generation time varies with: • Organism • Available nutrients • Temperature • pH, etc. • Can be short (10 min) or long (hours)

  20. II. Population growth, cont. • Case: • 1 cell • Generation time 30 min • In 10 hrs have 1,048,576 cells • 10 hrs = 20 generations • Get large numbers of cells quickly • Plot arithmetically or logarithmically

  21. Growth curve When a fresh medium is inoculated with a given number of cells, and the population growth is monitored over a period of time, plotting the data will yield a typical bacterial growth curve

  22. II. Population growth, cont. • Phases of growth: • 1. Lag phase • Cells are adjusting to environment. • Cells are synthesizing needed macromolecules. • 2. Log phase or exponential phase • Cells are undergoing binary fission.

  23. II. Population growth, cont. • 3.Stationary phase • Growth rate slows down. • Some cells die. • Due to depletion of nutrients and/or accumulation of waste • 4. Death phase • Cells die.

  24. Thank You

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