Lecture 4 Nutrition and Growth (Text Chapters: 5.1-5.3; 6.1; 6.4-6.8; 6.10-6.15)
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Transcript of Lecture 4 Nutrition and Growth (Text Chapters: 5.1-5.3; 6.1; 6.4-6.8; 6.10-6.15)
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Lecture 4Nutrition and Growth
(Text Chapters: 5.1-5.3; 6.1; 6.4-6.8; 6.10-6.15)
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Microbial Nutrition
• Why is nutrition important?
– The hundreds of chemical compounds present inside a living cell are formed from nutrients.
• Macronutrients : elements required in fairly large amounts
• Micronutrients : metals and organic compounds needed in very small amounts
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Main Macronutrients
• Carbon (C, 50% of dry weight) and nitrogen (N, 12% of
dry weight)
• Autotrophs are able to build all of their cellular organic
molecules from carbon dioxide
• Nitrogen mainly incorporated in proteins, nucleic acids
• Most Bacteria can use NH3 and many can also use NO3-
• Nitrogen fixers can utilize atmospheric nitrogen (N2)
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Other Macronutrients
• Phosphate (P), sulfur (S), potassium (K), magnesium
(Mg), calcium (Ca), sodium (Na), iron (Fe)
• Iron plays a major role in cellular respiration, being a
key component of cytochromes and iron-sulfur
proteins involved in electron transport.
• Siderophores : Iron-binding agents that cells
produce to obtain iron from various insoluble
minerals.
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Representative Siderophore
Ferric enterobactin
Aquachelin
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Micronutrients Need very little amount but critical to cell function.Often used as enzyme cofactors
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Growth factors Organic compounds, required in very small amount and then only by some cells
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Culture Media: Composition
• Culture media supply the nutritional needs of microorganisms– defined medium : precise amounts of highly purified
chemicals
– complex medium(or undefined) : highly nutritious substances.
• Inclinical microbilogy,– Selective : contains compunds that selectively inhibit
– Differential: contains indicator
– terms that describe media used for the isolation of particular species or for comparative studies of microorganisms.
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Culture Media: Physical Properties
• Liquid– Bouillon or broth
• Solid– Addition of a gelling agent (typically 1% agar) to liquid
media– Immobilize cells, allowing them to grow and form visible,
isolated masses called colonies (Figure 5.2).
• Semisolid– Reduced amount of agar added– Allows motile microorganism to spread
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Bacterial Colonies on Solid Media
S. Marcescens (Mac)
P. aeruginosa (TSA)
S. Flexneri (Mac)
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Laboratory Culture of Microorganisms
• Microorganisms can be grown in the laboratory
in culture media containing the nutrients they
require.
• Successful cultivation and maintenance of pure
cultures of microorganisms can be done only if
aseptic technique is practiced to prevent
contamination by other microorganisms.
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Microbial Growth
Binary fission
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• Microbial growth
involves an increase in
the number of cells.
• Growth of most
microorganisms occurs
by the process of binary
fission
Cell Growth and Binary Fission
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Microbial Growth
Peptidoglycan layerPeptidoglycan layer
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• Microbial populations
show a characteristic
type of growth pattern
called exponential
growth, which is best
seen by plotting the
number of cells over
time on a semi-
logarithmic graph.
Microbial Growth pattern
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Growth Curve
• Microorganisms show a characteristic growth pattern (Figure 6.8) when inoculated into a fresh culture medium.
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Measuring Microbial Growth
• Growth is measured by the change in the number
of cells over time.
– Cell counts done microscopically (Figure 6.9) measure
the total number of cells in a population
– whereas viable cell counts (plate counts) (Figures
6.10, 6.11) measure only the living, reproducing
population.
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Total Cell Count
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Viable Cell Count: Determination of Colony Forming Units
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Serial Dilution of Cells
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Indirect Cell Number Measurement : Turbidity
• Turbidity measurements are an indirect but very
rapid and useful method of measuring microbial
growth (Figure 6.12). However, to relate a
direct cell count to a turbidity value, a standard
curve must first be established.
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Turbidity Measurements of Microbial Growth
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Environmental Effects on Bacterial Growth
• Temperature
• pH
• Osmotic pressure
• Oxygen classes
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Temperature and Microbial Growth
• Cardinal temperatures – minimum– optimum – maximum
• Temperature is a major environmental factor controlling microbial growth.
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Classification of Microorganisms by Temperature Requirements
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Temperature Classes of Organisms
• Mesophiles– Midrange temperature optima– Found in warm-blooded animals and in terrestrial and aquatic
environments in temperate and tropical latitudes
• Psychrophiles– Cold temperature optima– Most extreme representatives inhabit permanently cold
environments
• Thermophiles– Growth temperature optima between 45ºC and 80ºC
• Hyperthermophiles– Optima greater than 80°C– These organisms inhabit hot environments including boiling hot
springs, as well as undersea hydrothermal vents that can have temperatures in excess of 100ºC
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Heat-Stable Macromolecules
• Thermophiles and hyperthermophiles
produce heat-stable macromolecules,
such as Taq polymerase, which is used to
automate the repetitive steps in the
polymerase chain reaction (PCR)
technique.
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pH and Microbial Growth
• The acidity or alkalinity of an environment can greatly affect
microbial growth.
• Most organisms grow best between pH 6 and 8, but some
organisms have evolved to grow best at low or high pH. The
internal pH of a cell must stay relatively close to neutral
even though the external pH is highly acidic or basic.
– Acidophiles : organisms that grow best at low pH
– Alkaliphiles : organismsa that grow best at high pH
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Osmotic Effects on Microbial Growth
• Osmotic pressure depends on the surrounding solute
concentration and water availability
• Water availability is generally expressed in physical
terms such as water activity
• Water activity is the ratio of the vapor pressure of the
air in equilibrium with a substance or solution to the
vapor pressure of pure water.
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Halophiles and Related Organisms
• In nature, osmotic effects are of interest mainly in habitats
with high salt environments that have reduced water
availability
• Halophiles : have evolved to grow best at reduced water
potential, and some (extreme halophiles) even require
high levels of salts for growth.
• Halotolerant : can tolerate some reduction in the water
activity of their environment but generally grow best in the
absence of the added solute
• Xerophiles : are able to grow in very dry environments
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Oxygen and Microbial Growth
• Aerobes :– Obligate : require oxygen to grow
– Facultative : can live with or without oxygen but grow better with oxygen
– Microaerphiles : require reduced level of oxygen
• Anaerobes :– Aerotolerant anaerobes : can tolerate oxygen but grow
better without oxygen.
– Obligate : do not require oxygen. Obligate anaerobes are killed by oxygen
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Test for Oxygen Requirements of Microorganisms
Thioglycolate broth : contains a reducing agent and provides aerobic and anaerobic conditions
a) Aerobic
b) Anaerobic
c) Facultative
d) Microaerophil
e) Aerotolerant
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Toxic Forms of Oxygen and Detoxifying Enzymes
HydrogenHydrogenperoxideperoxide
SuperoxideSuperoxide
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http://www.calstatela.edu/faculty/hpark8/http://www.calstatela.edu/faculty/hpark8/