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Microbial Growth

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Chapter 6 Microbial Growth What are Populations Colonies What are Populations Colonies Deep-freezing: -50 to -95 C Lyophilization (freeze-drying): Frozen (-54 to ... – PowerPoint PPT presentation

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Title: Microbial Growth


1
Chapter 6
  • Microbial Growth

2
  • Microbial growth increase in number of cells,
    not cell size

3
What are
  • Populations
  • Colonies

4
The Requirements for Growth
  • Physical requirements
  • Temperature
  • pH
  • Osmotic pressure
  • Chemical requirements
  • Carbon
  • Nitrogen, sulfur, and phosphorous
  • Trace elements
  • Oxygen
  • Organic growth factor

5
The Requirements for Growth Physical Requirements
  • Temperature
  • Minimum growth temperature
  • Optimum growth temperature
  • Maximum growth temperature

6
Temperature
Figure 6.1
7
Psychrotrophs
  • Grow between 0C and 20-30C
  • Cause food spoilage

8
Psychrotrophs
Figure 6.2
9
The Requirements for Growth Physical Requirements
  • pH
  • Most bacteria grow between pH 6.5 and 7.5
  • Molds and yeasts grow between pH 5 and 6
  • Acidophiles grow in acidic environments

10
The Requirements for Growth Physical Requirements
  • Osmotic Pressure
  • Hypertonic environments, increase salt or sugar,
    cause plasmolysis
  • Extreme or obligate halophiles require high
    osmotic pressure
  • Facultative halophiles tolerate high osmotic
    pressure

11
The Requirements for Growth Physical Requirements
Figure 6.4
12
The Requirements for Growth Chemical Requirements
  • Carbon
  • Structural organic molecules, energy source
  • Chemoheterotrophs use organic carbon sources
  • Autotrophs use CO2

13
  • 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

14
  • Trace Elements
  • Inorganic elements required in small amounts
  • Usually as enzyme cofactors

15
  • Oxygen (O2)

Obligate aerobes Faultative anaerobes Obligate anaerobes Aerotolerant anaerobes Microaerophiles

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
Biofilms
  • Microbial communities
  • Form slime or hydrogels
  • Bacteria attracted by chemicals via quorum
    sensing

Figure 6.5
18
The Requirements for Growth Chemical Requirements
  • Organic Growth Factors
  • Organic compounds obtained from the environment
  • Vitamins, amino acids, purines, pyrimidines

19
Culture Media
  • Culture Medium Nutrients prepared for microbial
    growth
  • Sterile No living microbes
  • Inoculum Introduction of microbes into medium
  • Culture Microbes growing in/on culture medium

20
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

21
Culture Media
  • Chemically Defined Media Exact chemical
    composition is known
  • Complex Media Extracts and digests of yeasts,
    meat, or plants
  • Nutrient broth
  • Nutrient agar

22
Culture Media
Table 6.2 6.4
23
Anaerobic Culture Methods
  • Reducing media
  • Contain chemicals (thioglycollate or oxyrase)
    that combine O2
  • Heated to drive off O2

24
An Anaerobic Chamber
Figure 6.7
25
Anaerobic Culture Methods
  • Anaerobic jar

Figure 6.5
26
Capnophiles require high CO2
  • Candle jar
  • CO2-packet

Figure 6.7
27
Biosafety Levels
  • 1 No special precautions
  • 2 Lab coat, gloves, eye protection
  • 3 Biosafety cabinets to prevent airborne
    transmission
  • 4 Sealed, negative pressure
  • Exhaust air is filtered twice

28
Biosafety Level 4 (BSL-4) Laboratory
Figure 6.8
29
Selective Media
  • Suppress unwanted microbes and encourage desired
    microbes.

Figure 6.9b, c
30
Differential Media
  • Make it easy to distinguish colonies of different
    microbes.

Figure 6.9a
31
Enrichment Media
  • Encourages growth of desired microbe
  • Assume a soil sample contains a few
    phenol-degrading bacteria and thousands of other
    bacteria
  • Inoculate phenol-containing culture medium with
    the soil and incubate
  • Transfer 1 ml to another flask of the phenol
    medium and incubate
  • Transfer 1 ml to another flask of the phenol
    medium and incubate
  • Only phenol-metabolizing bacteria will be growing

32
  • 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)

33
Streak Plate
Figure 6.10a, b
34
Preserving Bacteria Cultures
  • Deep-freezing -50to -95C
  • Lyophilization (freeze-drying) Frozen (-54 to
    -72C) and dehydrated in a vacuum

35
Reproduction in Prokaryotes
  • Binary fission
  • Budding
  • Conidiospores (actinomycetes)
  • Fragmentation of filaments

36
Binary Fission
Figure 6.11
37
Figure 6.12b
38
  • If 100 cells growing for 5 hours produced
    1,720,320 cells

39
Figure 6.13
40
Phases of Growth
ANIMATION Bacterial Growth Curve
Figure 6.15
41
Direct Measurements of Microbial Growth
  • Plate Counts Perform serial dilutions of a sample

Figure 6.15, top portion
42
Plate Count
  • Inoculate Petri plates from serial dilutions

Figure 6.16
43
Plate Count
  • After incubation, count colonies on plates that
    have 25-250 colonies (CFUs)

Figure 6.15
44
Direct Measurements of Microbial Growth
  • Filtration

Figure 6.17a, b
45
Direct Measurements of Microbial Growth
  • Multiple tube MPN test
  • Count positive tubes and compare to statistical
    MPN table.

Figure 6.18b
46
Direct Measurements of Microbial Growth
  • Direct Microscopic Count

47
Direct Measurements of Microbial Growth
Figure 6.19
48
Estimating Bacterial Numbers by Indirect Methods
  • Turbidity

Figure 620
49
Estimating Bacterial Numbers by Indirect methods
  • Metabolic activity
  • Dry weight
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