Download File - Microbiology

PowerPoint to accompany
Microbiology:
A Systems Approach
Cowan/Talaro
Chapter 7
Elements of Microbial
Nutrition, Ecology, and
Growth
Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Chapter 7
Topics
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Microbial Nutrition
Transport Across the Membrane
Environmental Factors
Microbial Growth
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Table 7.1
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Microbial Nutrition
• Definitions
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Nutrition
Essential nutrient
Macronutrient
Micronutrient
Inorganic nutrient
Organic nutrient
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Bacteria are composed of different elements and molecules, with
water (70%) and proteins (15%) being the most abundant.
Table 7.2 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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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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Sources of Essential Nutrients
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Nitrogen
Oxygen
Hydrogen
Phosphorous
Sulfur
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Miscellaneous Nutrients
• Mineral Ions
– K, Na, Ca, Mg, Z
• Trace Elements
– Cu, Co, Ni, Mb, Mn, Si, B, I
• Growth Factors
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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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Nutritional Types
• Carbon Source
– Organic – “Hetero”
– Inorganic – “Auto”
• Energy Source
– Light – “Photo”
– Chemical – “Chemo”
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Energy source
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Photoautotrophs
Chemoautotrophs
Photoheterotrophs
Chemoheterotrophs
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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, cyanobacteria
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Fig. 4.27b
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Chemoautotrophs
• Carbon Source is Inorganic ( CO2)
• Two types
– Chemical Energy can be organic or
inorganic
• Ex. Methanogens, Lithoautotrophs
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Methanogens are an example of a chemoautotroph.
Fig. 7.1 Methane-producing archaea
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Photoheterotrophs
• Light energy
• Organic Carbon Source
• Purple & Green Photosyntheic Bacteria
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Fig. 4.28
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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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Representation of a saprobe and its mode of action.
Fig. 7.2 Extracellular digestion in a saprobe with a cell wall.
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Summary of the different nutritional categories based on carbon
and energy source.
Table 7.3 Nutritional categories of microbes by energy
and carbon source.
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Transport mechanisms
• Osmosis
• Passive Transport
– Simple Diffusion
– Facilitated 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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Representation of the osmosis process.
Fig. 7.3 Osmosis, the diffusion of water through a selectively
permeable membrane
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Cells with- and without cell walls, and their responses to different
osmotic conditions (isotonic, hypotonic, hypertonic).
Fig. 7.4 Cell responses to solutions of differing osmotic
content.
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Fig. 7.4
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Fig. i7.p211a
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Diffusion
• Net movement of molecules from a high
concentrated area to a low concentrated
area
• No energy is expended (passive)
• Concentration gradient and permeability
affect movement
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A cube of sugar will diffuse from a concentrated area into a more
dilute region, until an equilibrium is reached.
Fig. 7.5 Diffusion of molecules in aqueous solutions
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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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Representation of the facilitated diffusion process.
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Fig. 7.6 Facilitated diffusion
Active transport
• Transport of molecules against a
gradient
• Requires energy (active)
• Requires a transport protein
• sugars, amino acids, organic acids,
phosphates and metal ions.
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Fig. 7.7a
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Fig. 7.7b
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Endocytosis
• Substances are taken in, but are not
transported through the membrane.
• Requires energy (active)
• Common for eucaryotes
– Phagocytosis – solid particles
– Pinocytosis - liquids
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Fig. 7.7c
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Example of the permease, group translocation, and endocytosis
processes.
Fig. 7.7 Active transport
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Summary of the transport processes in cells.
Table 7.4 Summary of transport processes in cells
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Environmental Factors
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Temperature
Gas
pH
Osmotic pressure
Other environmental factors
Microbial associations
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Temperature
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For optimal growth and metabolism
Psychrophile – 0 to 15 °C
Psychrotrophs – 20-30°C
Mesophile20 to 40 °C
Thermophile- 45 to 80 °C
Hyperthermophiles - > 80° C
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Growth and metabolism of different ecological groups based on
ideal temperatures.
Fig. 7.8 Ecological groups by temperature
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Example of a psychrophilic photosynthetic Red snow organism.
Fig. 7.9 Red snow
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Gas
• Two gases that most influence microbial
growth
– Oxygen
• Respiration
• Oxidizing agent
– Carbon dioxide
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Oxidizing agent
• Oxygen metabolites are toxic
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Singlet Oxygen
Superoxide Free Radicals
Hydrogen Peroxide
Hydroxyl Radicals
• These toxic metabolites must be
neutralized for growth
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Five categories of bacteria
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Obligate aerobe
Facultative anaerobe
Obligate anaerobe
Aerotolerant Anaerobes
Microaerophiles
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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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Aerotolerant Anaerobes
• Can tolerate oxygen but don’t
use it for growth
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Microaerophiles
• Require Oxygen, but only in small
amounts
• Don’t make enough enzymes to
detoxify toxic forms of oxygen if
they are exposed to normal
atmosphere
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Anaerobes must grow in an oxygen minus environment, because
toxic oxygen metabolites cannot be neutralized.
Fig. 7.10 Culturing technique for anaerobes
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Thioglycollate broth enables the identification of aerobes,
facultative anaerobes, and obligate anaerobes.
Reducing Media
Fig. 7.11 Use of
thioglycollate broth to
demonstrate
oxygen requirements.
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Fig. 7.10b
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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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Osmotic pressure
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Halophiles
Withstand hypertonic conditions
Some requires high salt concentrations
Ex. Halobacterium
Some can survive high salt conditions
but is not required
– Ex. Staphylococcus aureus
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Other factors
• Radiation- Spores or pigments help
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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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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An example of commensalism, where Staphylococcus aureus
provides vitamins and amino acids to Haemophilus influenzae.
Fig. 7.12 Satellitism, a
type of commensalism
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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, and
synergistic
• Normal Microbial Flora are beneficial
– Mutualistic
– Ex. E. coli produce vitamin K for the host
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Microbial Growth
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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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Representation of the steps in binary fission of a rod-shaped
bacterium.
Fig. 7.13 Steps in binary fission of a rod-shaped bacterium.
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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 are used to define the
numbers of bacteria after growth
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Representation of how a single bacterium doubles after a
complete division, and how this can be plotted using exponentials.
Fig. 7.14 The mathematics of population growth
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Fig. 7.14b
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Growth curve
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Lag phase
Log phase
Stationary phase
Death phase
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Lag phase
• Cells are adjusting, enlarging, and
synthesizing critical proteins and
metabolites
• Not doubling at their maximum growth
rate
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Log phase
• Maximum exponential growth rate of
cell division
• Adequate nutrients
• Favorable environment
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Stationary phase
• Survival mode – depletion in nutrients,
released waste can inhibit growth
• When the number of cells that stop
dividing equal the number of cells that
continue to divide
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Death phase
• A majority of cells begin to die
exponentially due to lack of nutrients
• A chemostat will provide a continuous
supply of nutrients, thereby the death
phase is never achieved.
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The four main phases of growth in a bacterial culture.
Fig. 7.15 The growth curve in a bacterial culture.
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Measuring Microbial Growth
• Direct Methods
– Plate Counts
– Direct cell count
– Automated devices
• Coulter counter
• Flow cytometer
• Indirect Methods
– Turbidity
• Spectrophotometer
– Measure Metabolic Activity
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Fig. i7.6
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The direct cell method counts the total dead and live cells in a
special microscopic slide containing a premeasured grid.
Fig. 7.17 Direct microscopic count of bacteria.
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A Coulter counter uses an electronic sensor to detect and count
the number of cells.
Fig. 7.18 Coulter counter
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The greater the turbidity, the larger the population size.
Fig. 7.16 Turbidity measurements as indicators of growth
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