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Microbial Growth

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Inward movement of cell wall and cell membrane dividing daughter cells ... Lyophilization (freeze-drying): Frozen (-54 to -72 C) and dehydrated in a vacuum ... – PowerPoint PPT presentation

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Title: Microbial Growth


1
Microbial Growth
2
The Cell Cycle
3
Microbial Growth and Cell Division
  • Increase in mass
  • Increase in cell numbers
  • Mitosis in most eukaryotes
  • Budding in yeasts
  • Fragmentation in filamentous fungi
  • Binary fission in bacteria

4
Steps in Binary Fission
  • Chromosome replication
  • Chromosome attachment to cell membrane.
  • Chromosomal segregation
  • Septum formation
  • Inward movement of cell wall and cell membrane
    dividing daughter cells
  • Wall Elongation

5
Binary Fission
6
Bacterial Chromosome Replication
  • Semiconservative
  • Results in one new and one parental strand
  • In Escherichia coli
  • Bidirectionally from single origin
  • Initiates replication
  • Controls frequency of initiation events
  • Segregates replicated chromosomes to daughter
    cells

7
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8
The Requirements for Growth Physical Requirements
  • Temperature
  • Minimum growth temperature
  • Optimum growth temperature
  • Maximum growth temperature

9
Temperature Ranges
10
Figure 6.2
11
The Requirements for Growth Chemical Requirements
  • Carbon
  • Structural organic molecules, energy source
  • Chemoheterotrophs use organic carbon sources
  • Autotrophs use CO2

12
The Requirements for Growth Chemical Requirements
  • Nitrogen
  • In amino acids, proteins
  • Most bacteria decompose proteins
  • Some bacteria use NH4 or NO3?
  • A few bacteria use N2 in nitrogen fixation
  • Sulfur
  • In amino acids, thiamine, biotin
  • Most bacteria decompose proteins
  • Some bacteria use SO42? or H2S
  • Phosphorus
  • In DNA, RNA, ATP, and membranes
  • PO43? is a source of phosphorus

13
The Requirements for Growth Chemical Requirements
  • Trace Elements
  • Inorganic elements required in small amounts
  • Usually as enzyme cofactors

14
The Requirements for Growth Chemical Requirements
  • Oxygen (O2)

obligate aerobes Faultative anaerobes Obligate anaerobes Aerotolerant anaerobes Microaerophiles

15
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16
Toxic Forms of Oxygen
  • Singlet oxygen O2 boosted to a higher-energy
    state
  • Superoxide free radicals O2?
  • Peroxide anion O22?
  • Hydroxyl radical (OH?)

17
The Requirements for Growth Chemical Requirements
  • Organic Growth Factors
  • Organic compounds obtained from the environment
  • Vitamins, amino acids, purines, pyrimidines

18
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19
Logistic Growth
  • Exponential growth is optimal, real growth
    follows a logistic pattern
  • Lag phase
  • A period when cells are metabolizing but not
    dividing yet
  • Log phase
  • Exponential growth
  • Stationary phase
  • Equal numbers of cells are dividing and dying
  • Death phase
  • Culture dies exponentially

20
Bacterial Growth Curve
21
Requirements for Culturing Bacteria
  • Culture Medium Nutrients prepared for microbial
    growth
  • Sterile No living microbes
  • Inoculum Introduction of microbes into medium
  • Culture Microbes growing in/on culture medium

22
Isolation and Pure Culture
  • A pure culture contains only one species or
    strain
  • A colony is a population of cells arising from a
    single cell or spore or from a group of attached
    cells
  • A colony is often called a colony-forming unit
    (CFU)

23
Isolation Methods
  • 1.      Streak Plate
  • 2.      Pour plate

24
Streak Plate
Figure 6.10a, b
25
General Types of Culture Media
26
Culture Media
  • Chemically Defined Media Exact chemical
    composition is known
  • Complex Media Extracts and digests of yeasts,
    meat, or plants
  • Nutrient broth
  • Nutrient agar

27
Culture Media
Table 6.2 6.4
28
Agar
  • Complex polysaccharide
  • Used as solidifying agent for culture media in
    Petri plates, slants, and deeps
  • Generally not metabolized by microbes
  • Liquefies at 100C
  • Solidifies 40C

29
Incubation Techniques
  • Temperature
  • Oxygen Content
  • Reducing Media
  •  Anaaerobic jar
  •  Anaerobic glove box
  • Candle jar

30
Anaerobic Culture Methods
  • Reducing media
  • Contain chemicals (thioglycollate or oxyrase)
    that combine O2
  • Heated to drive off O2

31
Anaerobic Culture Methods
  • Anaerobic jar

Figure 6.5
32
Anaerobic Culture Methods
  • Anaerobic chamber

Figure 6.6
33
Capnophiles require high CO2
  • Candle jarCO2-packet

Figure 6.7
34
 
Special Types of Media
  • Selective 
  • Differential
  • Selective/ Differential
  • Enrichment

35
Selective Media
  • Suppress unwanted microbes and encourage desired
    microbes.

Figure 6.9b, c
36
Differential Media
  • Make it easy to distinguish colonies of different
    microbes.

Figure 6.9a
37
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38
Direct Measurements of Microbial Growth
  • Plate Counts Perform serial dilutions of a sample

Figure 6.15, top portion
39
Plate Count
  • Inoculate Petri plates from serial dilutions

Figure 6.16
40
Plate Count
  • After incubation, count colonies on plates that
    have 25-250 colonies (CFUs)

Figure 6.15
41
Direct Measurements of Microbial Growth
  • Filtration

Figure 6.17a, b
42
Direct Measurements of Microbial Growth
  • Multiple tube MPN test
  • Count positive tubes and compare to statistical
    MPN table.

Figure 6.18b
43
Direct Measurements of Microbial Growth
  • Direct Microscopic Count

44
Direct Measurements of Microbial Growth
Figure 6.19
45
Estimating Bacterial Numbers by Indirect Methods
  • Turbidity

Figure 620
46
Estimating Bacterial Numbers by Indirect methods
  • Metabolic activity
  • Measure a metabolic product
  • CO2
  • Dry weight

47
Preserving Bacteria Cultures
  • Deep-freezing -50to -95C
  • Lyophilization (freeze-drying) Frozen (-54 to
    -72C) and dehydrated in a vacuum
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