Download Microbial Nutrition

Topic 10 (Ch7)
Elements of Microbial Nutrition,
Ecology, and Growth
Topics
– Microbial Nutrition
– Environmental Factors
– Microbial Growth
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Microbial Nutrition
• Chemical analysis
• Sources of essential nutrients
• Transport mechanisms
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Bacteria are composed of different elements and molecules, with
water (70%) and proteins (15%) being the most abundant.
Analysis of the chemical composition of an E. coli cell.
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Sources of essential nutrients
• Required for metabolism and growth
– Carbon source
– Energy source
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Defined by Carbon Source
• Heterotroph
(depends on other life forms)
– Organic molecules
– Ex. Sugars, proteins, lipids
• Autotroph
(self-feeders)
– Inorganic molecules
– Ex. CO2
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Growth factors
• Essential organic nutrients
• Not synthesized by the microbe, and
must be supplemented
• Ex. Amino acids, vitamins
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2
Energy source
• Chemoheterotrophs
• Photoautotrophs
• Chemoautotrophs
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Chemoheterotrophs
• Derive both carbon and energy from
organic compounds
– Saprobic
• decomposers of plant litter, animal matter, and
dead microbes
– Parasitic
• Live in or on the body of a host
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Photoautotroph
• Derive their energy from sunlight
• Transform light rays into chemical
energy
• Primary producers of organic matter for
heterotrophs
• Primary producers of oxygen
• Ex. Algae, plants, some bacteria
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3
Chemo organic autotrophs
• Two types
– Chemo organic autotroph
• Derives their energy from organic compounds
and their carbon source from inorganic
compounds
– Lithoautotrophs
• Neither sunlight nor organics used, rather it
relies totally on inorganics
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Saprobe mode of action
Extracellular digestion in a saprobe with a cell wall.
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Nutritional categories summary
(based on carbon and energy source)
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4 Transport mechanisms
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Osmosis
Diffusion
Active transport
Endocytosis
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Osmosis
• Diffusion of water
through a
permeable but
selective membrane
• Water moves toward
the higher solute
concentrated areas
– Isotonic
– Hypotonic
– Hypertonic
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Diffusion
• Net molecule movement
from high concentration
area to low concentration
area
• No energy is expended
(passive)
• Concentration gradient and
permeability affect
movement
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5
Facilitated diffusion
• Transport of polar
molecules and ions
across the membrane
• No energy is expended
(passive)
• Carrier protein
facilitates the binding
and transport
– Specificity
– Saturation
– Competition
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Active transport
• Transport of molecules against a
gradient
• Requires energy (active)
• Ex. Permeases and protein pumps
transport sugars, amino acids, organic
acids, phosphates and metal ions.
• Ex. Group translocation transports and
modifies specific sugars
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Endocytosis
• Substances are taken, but are not
transported through the membrane.
• Requires energy (active)
• Common for eukaryotes
• Ex. Phagocytosis, pinocytosis
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Active transport examples
permease
group
translocation
endocytosis
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Cell transport process summary
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Environmental Factors
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•
•
•
•
•
Temperature
Gas
pH
Osmotic pressure
Other factors
Microbial association
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7
Temperature
optimal growth
and metabolism:
• Psychrophile –
0 to 15 °C
• Mesophile –
20 to 40 °C
• Thermophile45 to 80 °C
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Temperature & Growth
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Gas
• Two gases that most influence microbial
growth
– Oxygen
• Respiration
• Oxidizing agent
(adds O2 to a compound with a loss of
electrons)
– Carbon dioxide
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8
Oxidizing agent
• Oxygen metabolites are toxic
• These toxic metabolites must be
neutralized for growth
• Three categories of bacteria
– Obligate aerobe
– Facultative anaerobe
– Obligate anaerobe
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Obligate aerobe
• Requires oxygen for metabolism
• Possess enzymes that can neutralize
the toxic oxygen metabolites
– Superoxide dismutase and catalase
• Ex. Most fungi, protozoa, and bacteria
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Facultative anaerobe
• Does not require oxygen for
metabolism, but can grow in its
presence
• During minus oxygen states, anaerobic
respiration or fermentation occurs
• Possess superoxide dismutase and
catalase
• Ex. Gram negative pathogens
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Obligate anaerobes
• Cannot use oxygen for metabolism
• Do not possess superoxide dismutase
and catalase
• The presence of oxygen is toxic to the
cell
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Thioglycollate broth shows aerobes, facultative anaerobes, and
obligate anaerobes.
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pH
• Cells grow best between pH 6-8
• Exceptions would be acidophiles (pH 0),
and alkalinophiles (pH 10).
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10
Osmotic pressure
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•
•
•
•
Halophiles
Requires high salt concentrations
Withstands hypertonic conditions
Ex. Halobacterium
Facultative halophiles
– Can survive high salt conditions but is not
required
– Ex. Staphylococcus aureus
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Other factors
• Radiation- withstand UV, infrared
• Barophiles – withstand high pressures
• Spores and cysts- can survive dry
habitats
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Ecological association
• Influence microorganisms have on other
microbes
– Symbiotic relationship
– Non-symbiotic relationship
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3 Types of Symbiotic
Relationships
Symbiotic:
Organisms that live in close nutritional relationship
• Types
– Mutualism – both organism benefit
– Commensalism – one organisms benefits
– Parasitism – host/microbe relationship
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2 Types of Non-symbiotic
Relationships
Non-symbiotic: Organisms are free-living, and
do not rely on each other for survival
• Types
– Synergism – shared metabolism, not
required
– Antagonism- competition between
microorganisms
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Interrelationships between
microbes and humans
• Can be commensal, parasitic,
synergistic
• Ex. E. coli produce vitamin K for the
host
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Microbial Growth
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•
•
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Binary fission
Generation time
Growth curve
Enumeration of bacteria
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Binary fission
• The division of a bacterial cell
• Parental cell enlarges and duplicates its
DNA
• Septum formation divides the cell into
two separate chambers
• Complete division results in two
identical cells
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Generation time
• The time required for a
complete division cycle
(doubling)
• Length of the
generation time is a
measure of the growth
rate
• Exponentials (logs)
used to define numbers
of bacteria
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Mathematics of population growth from a single
bacterium
# of bacteria = 2n , where n = the # of divisions
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Growth curve
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Lag phase
Log phase
Stationary phase
Death phase
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Enumeration of bacteria
• Turbidity
• Direct cell count
• Automated devices
– Coulter counter
– Flow cytometer
– Real-time PCR
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