1. Binary fission Procaryotic cell division: –Binary fission is the process by which most procaryotes replicate. –Binary fission generally involves the separation of a single cell into two more or less identical daughter cells, each containing, among other things, at least one copy of the parental DNA. –Stepwise process: The first steps of binary fission include cell elongation and DNA replication. The cell envelope then pinches inward, eventually meeting. A cross wall is formed and ultimately two distinct cells are present, each essentially identical to the original parent cell.

3. Generation time [doubling time] Procaryotic cell division: A bacterial generation time is also know as its doubling time. Doubling time is the time it takes a bacterium to do one binary fission starting from having just divided and ending at the point of having just completed the next division. binary fission Generation times vary with organism and environment and can range from 20 minutes for a fast growing bacterium under ideal conditions, to hours and days for less than ideal conditions or for slowly growing bacteria. Definition: The generation time is the time it takes for the number of cells in a culture to double. It is usually determined only during exponential phase growth.

4. Generation Time Two ways one can determine: – [1] mathematically – [2] graphically Graphical Determination of Generation Time. Plot the number of cells/ml against time is plotted on semi-log paper. – X-axis (time) on linear scale – Y-axis (number cells/ml) on logarithmic scale Generation time is determined by the time it takes the number of cells to double.

6. Time after inoc (h)Cell NumberLog 01 x10 2 2.0 12.4 x10 2 ~ 2.3 24.8 x10 2 ~2.6 38.5 x10 2 ~2.9 41.6 x 10 3 ~3.2 53.2 x 10 3 ~3.5 66.4 x 10 3 ~3.8 71.28 x 10 4 ~4.1 Plot the following on log linear paper

7. Calculating Generation time 2 number of generations - describes how the cells increase exponentially Initial number of cells x 2 number of generations = final cell concentration e.g. if 5 cells divided 9 times 5 x 2 9 =2560 cells To calc. the number of generations, cell numbers must be converted to logs No. of generations= log cell # at end –log cell number at start 0.301 (Note: 0.301 is log of 2) To calc generation time for a population 60min/hr x hours = minutes/generation Number of generations

8. To calc generation time for a population 60min/hr x hours = minutes/generation Number of generations e.g. 100 bacteria growing for 5 hours produce 1720320 cells Log 1720320-log 100 = 14 generations 0.301 60min/hr x 5 hours = 21 minutes/generation 14 generations See page 877 Totora

9. Generation times for some common bacteria under optimal conditions of growth BacteriumMediumGeneration Time (minutes) Escherichia coliGlucose-salts17 Bacillus megateriumSucrose-salts25 Streptococcus lactisMilk26 Streptococcus lactisLactose broth48 Staphylococcus aureusHeart infusion broth27-30 Lactobacillus acidophilusMilk66-87 Rhizobium japonicumMannitol-salts-yeast extract344-461 Mycobacterium tuberculosisSynthetic792-932 Treponema pallidumRabbit testes1980