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Chapter 6: Microbial Growth

Chapter 6: Microbial Growth. How do bacteria grow?. Not in size Increase in population size One cell divides into 2 new cells – binary fission. Binary fission. Binary fission:. Attachment of chromosome to p.m.; replication of DNA; new p.m. and cell wall laid down between the 2 chromosomes

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Chapter 6: Microbial Growth

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  1. Chapter 6: Microbial Growth

  2. How do bacteria grow? • Not in size • Increase in population size • One cell divides into 2 new cells – binary fission

  3. Binary fission

  4. Binary fission: • Attachment of chromosome to p.m.; replication of DNA; new p.m. and cell wall laid down between the 2 chromosomes • This is the way that each new daughter cell gets one chromosome

  5. How can we describe growth? 2n = no. of cells in n generation Generation time Nt = N0 x 2n

  6. Growth problems If Staphylococcus aureus has a doubling time (generation time) of 30 minutes and 5 hours have passed, how many generations have been produced? a. How many 30 minute time chunks are in 5 hours? = 10 ANSWER: 10 generations

  7. Growth problems If Staphylococcus aureus has a generation time of 30 minutes and 5 hours have passed, how many bacteria will be present at the end of the time period? • We have already determined that 10 generations will occur. • 2n = # cells at n generation • 210 = # cells at the 10th generation ANSWER = 1024 cells

  8. Growth problems If Staphylococcus aureus has a generation time of 30 minutes and 5 hours have passed, how many bacteria will be present at the end of the time period if we start with 3,000 cells? Nt = N0 x 2n Nt= 3,000 x 210 = 3,072,000 cells at the end of 5 hours

  9. Growth curve: lag, log, stationary, and death phases • What occurs in each?

  10. How can population size be counted? (Advantages and disadvantages of each method) 1. Direct methods A. Microscopic count with hemacytometer/ Petroff Hauser counting chamber

  11. Petroff Hauser counting chamber

  12. B. Plate counts – dilution series and plates

  13. C. Filtration

  14. D. Coulter counter/flow cytometer/Fluorescence activated cell sorter (FACS)

  15. 2. Indirect methods A. Dry weight B. Metabolic activity C. Turbidity

  16. Turbidity

  17. Growth requirements of microbes A. Temperature: Thermophiles Mesophiles Psychrophiles

  18. B. pH: acidophiles C. Osmotic pressure (# of solutes in solution) Halophiles D. Oxygen: Types: Obligate aerobe Facultative anaerobe Obligate anaerobe Aerotolerant anaerobe Microaerophilic

  19. Enzymes needed to survive in presence of oxygen: Catalase Peroxidase Super oxide dismutase (SOD)

  20. E. Nutrients C, N, P, S elements needed Mg, Fe, etc. trace elements needed Media: Defined or complex Selective vs. differential Special

  21. Mannitol salt agar – selective medium

  22. Blood agar – differential medium

  23. The End

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