Transcript Microbial Growth

Microbial Growth
The Cell Cycle
Microbial Growth and Cell
Division
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Increase in mass
Increase in cell numbers
Mitosis in most eukaryotes
 Budding in yeasts
 Fragmentation in filamentous fungi
 Binary fission in bacteria
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Steps in Binary Fission
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Chromosome replication
Chromosome attachment to cell
membrane.
Chromosomal segregation
Septum formation
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Inward movement of cell wall and cell membrane dividing
daughter cells
Wall Elongation
Binary Fission
Bacterial Chromosome
Replication
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Semiconservative
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Results in one new and one parental strand
In Escherichia coli
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Bidirectionally from single origin
Initiates replication
 Controls frequency of initiation events
 Segregates replicated chromosomes to
daughter cells
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The Requirements for
Growth: Physical
Requirements
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Temperature
Minimum growth temperature
 Optimum growth temperature
 Maximum growth temperature
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Temperature Ranges
Figure 6.2
The Requirements for Growth:
Chemical Requirements
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Carbon
Structural organic molecules, energy
source
 Chemoheterotrophs use organic carbon
sources
 Autotrophs use CO2
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The Requirements for Growth:
Chemical Requirements
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Nitrogen
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Sulfur
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In amino acids, proteins
Most bacteria decompose proteins
Some bacteria use NH4+ or NO3
A few bacteria use N2 in nitrogen fixation
In amino acids, thiamine, biotin
Most bacteria decompose proteins
Some bacteria use SO42 or H2S
Phosphorus
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In DNA, RNA, ATP, and membranes
PO43 is a source of phosphorus
The Requirements for Growth:
Chemical Requirements
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Trace Elements
Inorganic elements required in small
amounts
 Usually as enzyme cofactors
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The Requirements for Growth:
Chemical Requirements
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Oxygen (O2)
obligate
aerobes
Faultative
anaerobes
Obligate
anaerobes
Aerotolerant
Microaerophiles
anaerobes
Toxic Forms of Oxygen
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Singlet oxygen: O2 boosted to a higherenergy state
Superoxide free radicals: O2
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Peroxide anion: O22
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Hydroxyl radical (OH)
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The Requirements for Growth:
Chemical Requirements
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Organic Growth Factors
Organic compounds obtained from the
environment
 Vitamins, amino acids, purines, pyrimidines
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Logistic Growth
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Exponential growth is optimal, real growth
follows a logistic pattern
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Lag phase
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Log phase
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Exponential growth
Stationary phase
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A period when cells are metabolizing but not dividing yet
Equal numbers of cells are dividing and dying
Death phase
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Culture dies exponentially
Bacterial Growth Curve
Requirements for Culturing
Bacteria
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Culture Medium: Nutrients prepared
for microbial growth
Sterile: No living microbes
Inoculum: Introduction of microbes into
medium
Culture: Microbes growing in/on culture
medium
Isolation and Pure Culture
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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)
Isolation Methods
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1.
2.
Streak Plate
Pour plate
Streak Plate
Figure 6.10a, b
General Types of Culture Media
Culture Media
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Chemically Defined Media: Exact chemical
composition is known
Complex Media: Extracts and digests of
yeasts, meat, or plants
Nutrient broth
 Nutrient agar
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Culture Media
Table 6.2 & 6.4
Agar
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Complex polysaccharide
Used as solidifying agent for culture
media in Petri plates, slants, and deeps
Generally not metabolized by microbes
Liquefies at 100°C
Solidifies ~40°C
Incubation Techniques
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Temperature
Oxygen Content
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Reducing Media
Anaaerobic jar
Anaerobic glove box
Candle jar
Anaerobic Culture Methods
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Reducing media
Contain chemicals (thioglycollate or
oxyrase) that combine O2
 Heated to drive off O2
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Anaerobic Culture Methods
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Anaerobic jar
Figure 6.5
Anaerobic Culture Methods
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Anaerobic
chamber
Figure 6.6
Capnophiles require high CO2
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Candle jar
CO2-packet
Figure 6.7
Special Types of Media
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Selective
Differential
Selective/ Differential
Enrichment
Selective Media
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Suppress
unwanted
microbes and
encourage
desired
microbes.
Figure 6.9b, c
Differential Media
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Make it easy to distinguish colonies of
different microbes.
Figure 6.9a
Direct Measurements of
Microbial Growth
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Plate Counts: Perform serial dilutions of a
sample
Figure 6.15, top portion
Plate Count
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Inoculate
Petri plates
from serial
dilutions
Figure 6.16
Plate Count
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After incubation, count colonies on plates that have 25250 colonies (CFUs)
Figure 6.15
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Direct Measurements of Microbial
Growth
Filtration
Figure 6.17a, b
Direct Measurements of
Microbial Growth
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Multiple tube
MPN test
Count positive
tubes and
compare to
statistical MPN
table.
Figure 6.18b
Direct Measurements of
Microbial Growth
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Direct Microscopic
Count
Direct Measurements of
Microbial Growth
Figure 6.19
Estimating Bacterial Numbers by
Indirect Methods
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Turbidity
Figure 620
Estimating Bacterial Numbers
by Indirect methods
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Metabolic activity
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Measure a metabolic product
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CO2
Dry weight
Preserving Bacteria Cultures
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Deep-freezing: -50°to -95°C
Lyophilization (freeze-drying): Frozen
(-54° to -72°C) and dehydrated in a
vacuum