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The Growth of Bacterial Cultures. Ways of monitoring and measuring growth, directly and indirectly. Reproduction in Prokaryotes. Bacteria normally reproduce through Binary fission

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The Growth of Bacterial Cultures

  • Ways of monitoring and measuring growth, directly and indirectly
reproduction in prokaryotes
Reproduction in Prokaryotes
  • Bacteria normally reproduce through Binary fission
  • There are a few bacterial species that reproduce through Budding,Conidiospores (actinomycetes), or by Fragmentation
binary fission
Binary Fission

Figure 6.11

generation time
Generation Time

-Time required for cell to divide (and its population to double)

Figure 6.12b

  • If 5 cells were allowed to divide 9 times

Then, 5 x 29 = 2560 cells

  • To calculate the number of generations, you need to convert into logarithms. The log of 2 (0.301) is used because one cell divides into two

Refer to Appendix D of your textbook


If 100 cells growing for 5 hours produced 1,720,320 cells:

= log 1,720,320 – log 100 = 6.2356 - 2 =14 generations

0.301 0.301

= 60 minutes x 5 hours = 21minutes/generation

14 generations

*These calculations are useful to compare growth conditions


Phases of Growth

Figure 6.14

direct measurements of microbial growth
Direct Measurements of Microbial Growth
  • Plate Counts
  • Filtration
  • Direct Microscopic Count
direct measurements of microbial growth1
Direct Measurements of Microbial Growth
  • Plate Counts: Perform serial dilutions of a sample

Figure 6.15, top portion

plate count
Plate Count
  • Inoculate Petri plates from serial dilutions

Figure 6.16

plate count1
Plate Count
  • After incubation, count colonies on plates that have 25-250 colonies (CFUs)

Bacterial Lawn

Figure 6.15


Cell Viability Measurement: Spread Plate

Optimal number to count is 30-300 colonies

direct measurements of microbial growth3
Direct Measurements of Microbial Growth
  • Multiple tube MPN test
  • Count positive tubes and compare to statistical MPN table.

Figure 6.18b

indirect measurements of microbial growth
Indirect Measurements of Microbial Growth
  • Turbidity
  • Metabolic Activity
  • Dry weight

Optical Density Measurement

600nm to measure Pichia growth

estimating bacterial numbers by indirect methods1
Estimating Bacterial Numbers by Indirect Methods
  • Metabolic Activity

-measure product as a function of time

Example: Bacterial culture produces acid as a metabolic product, therefore you can monitor growth by monitoring change in pH over time.

  • Dry weight-filter all cells, dry in desiccator, and weigh on scale