Chapter 6: Microbial Growth
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Transcript of 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
This is the way that each new daughter cell gets one chromosome
Number of generations
Number of cells Log of # of cells10X = #
0 1 01 2 0.32 4 0.63 8 0.94 16 1.25 32 1.56 64 1.87 128 2.18 256 2.49 512 2.710 1024 3.011 2048 3.312 4096 3.6
How can we describe growth?
2n = no. of cells in n generation
Generation time
Nt = N0 x 2n
Growth problemsIf 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
Growth problemsIf 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?
a. We have already determined that 10 generations will occur.
b. 2n = # cells at n generationc. 210 = # cells at the 10th generation
ANSWER = 1024 cells
Growth problemsIf 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
Growth curve: lag, log, stationary, and death phases
What occurs in each?
How can population size be counted?(Advantages and disadvantages of each
method)
1. Direct methods
A. Microscopic count with hemacytometer/
Petroff Hauser counting chamber
Petroff Hauser counting chamber
B. Plate counts – dilution series and plates
C. Filtration
D. Coulter counter/flow cytometer/Fluorescence activated cell sorter (FACS)
2. Indirect methodsA. Dry weight
B. Metabolic activity
C. Turbidity
Turbidity
Growth requirements of microbesA. Temperature:
ThermophilesMesophilesPsychrophiles
B. pH: acidophilesC. Osmotic pressure (# of solutes in solution)
HalophilesD. Oxygen:
Types:Obligate aerobeFacultative anaerobeObligate anaerobeAerotolerant anaerobeMicroaerophilic
Enzymes needed to survive in presence of oxygen:
CatalasePeroxidaseSuper oxide dismutase (SOD)
E. Nutrients
C, N, P, S elements neededMg, Fe, etc. trace elements neededMedia:
Defined or complexSelective vs. differentialSpecial
Mannitol salt agar – selective medium
Blood agar – differential medium
The End