LECTURES IN
MICROBIOLOGY
Microbial Nutrition and Growth
LESSON 5
Sofronio Agustin
Professor
Lesson 5 Topics
 Microbial Nutrition
 Environmental Factors
 Microbial Growth
2
Microbial Nutrition
 Based on intake:
(a) Macronutrients (CHONPS)
(b)
Micronutrients (trace elements)
 Based on carbon content:
(a) Organic nutrients- contain carbon
(b) Inorganic nutrients- simple atom or
molecule without carbon
3
Chemical Composition
Bacteria are composed of different elements and molecules, with water
(70%) and proteins (15%) being the most abundant.
4
Essential Nutrients
Carbon source
Energy Source
Growth Factors
5
Carbon Source
 Autotrophs - obtain carbon from
inorganic molecules like CO2
 Heterotrophs - obtain carbon from
organic matter from other life forms
(e.g. sugar, proteins and lipids)
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Energy Source
Photoautotrophs and photoheterotrophs obtain
energy from sunlight
Chemoautotrophs derive electron energy from
reduced inorganic compounds
Chemoheterotrophs obtain electron energy from
hydrogen atoms of organic compounds
7
Nutritional Categories
Summary of different
nutritional categories of
microbes based energy
and carbon sources
8
Methanogens
Methanogens are
chemoautotrophic
microbes
Example: methane
producing Archaea
9
Extracellular Digestion
10
Cell Membrane
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Phospholipid bilayer with integral and peripheral proteins
“Fluid mosaic” model - phospholipids and proteins move
laterally
Exhibits “selective permeability”
11
Membrane Transport

Passive:
(a) Simple diffusion
(b) Facilitated diffusion
(c) Osmosis

Active:
(a) Permease
(b) Group translocation
(c) Endocytosis
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Simple Diffusion
 Net movement of solute from area of high
concentration to a low concentrated area
 No energy is expended
 Down the concentration gradient (like a
river flowing downstream)
13
Diffusion
A cube of sugar will
diffuse from a
concentrated area
into a more dilute
region, until an
equilibrium is
reached.
14
Facilitated Diffusion
Transport of polar molecules and ions
across the membrane down their
concentration gradients
No energy is expended (passive)
Carrier protein facilitates the binding and
transport
-Specificity
-Saturation
-Competition
15
Facilitated Diffusion
Facilitated Diffusion: The Process
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Osmosis
 Diffusion of solvent
(usually, water)
through a permeable
but selective
membrane
 Water tends to move
toward higher solute
concentrated areas
17
Tonicity
Fate of cells
in different
osmotic
conditions isotonic,
hypotonic,
and
hypertonic
solutions
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Active Transport
Transport of molecules against its concentration
gradient
Requires energy and transport protein
(Ex. Permeases and protein pumps
transport sugars, amino acids, organic
acids, phosphates and metal ions)
Group translocation transports and modifies
specific sugars
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Endocytosis
Large substances are taken in by the cell
but are not transported through the
membrane.
Requires energy (active)
Common in eukaryotes
- Phagocytosis
- Pinocytosis
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Active Transport
Example of permease, group translocation and endocytosis
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Cellular Transport : Summary
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Environmental Factors

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

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Temperature
Gas
pH
Osmotic pressure
Other factors
Microbial association
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Temperature
Psychrophiles – (cold loving) 0 to 15 °C
Psychrotrophs - (food spoilage) grow
between 20 to 30 °C
Mesophiles- (most human pathogens)
20 to 40 °C
Thermophiles- (heat loving) 45 to 80 °C
Themoduric - (contaminants of heated food)
survive in short exposures to high temp
Hyperthermophiles - (Archaea)
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Temperature Tolerance
25
Gas Requirements
 Two gases that influence microbial growth:
(1)Oxygen
 Respiration - terminal electron acceptor
 Oxidizing agent - toxic forms
(2)Carbon dioxide
26
Oxygen Metabolites
 Superoxide radical - O2  Singlet oxygen - O2 with single electron in its
valence shell
 H2O2
All are toxic byproducts of metabolism neutralized by
enzymes SOD (superoxide dismutase), peroxidase and
catalase.
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Bacterial Types
Obligate aerobe
Facultative anaerobe
Obligate anaerobe
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Obligate Aerobes
Require oxygen for metabolism
Possesses enzymes that can neutralize
the toxic oxygen metabolites:
SOD, peroxidase and catalase
Ex: Most fungi, protozoa, and bacteria
like Bacillus sp. and Pseudomonas sp.
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Obligate Anaerobes
Cannot use oxygen for metabolism
Do not possess SOD and catalase
The presence of oxygen is toxic to
the cell
Ex: Clostridium sp. and Bacteroides sp.
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Anaerobiosis
Anaerobic culture techniques: (a) anaerobic chamber, (b) anaerobic jar
31
Facultative Anaerobes
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. E. coli and S. aureus
32
Thioglycolate Broth
Thioglycollate broth is
used to demonstrate
aerotolerance of
bacteria.
Aerobes, facultative
anaerobes, and obligate
anaerobes can be
detected using this
medium.
33
Other Gas Requirements
 Microaerophiles - requires less than 10%
of atmospheric O2.
Ex: Campylobacter jejuni
 Capnophiles - requires increased CO2
(5-15%) tension for initial growth.
Ex: S. pneumoniae
34
pH
Most cells grow best between pH 6-8
Acidophiles (up to pH 0) - molds and
yeast
Alkalinophiles (up pH 10) ureadecomposing bacteria like Proteus sp.
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Osmotic Pressure
Osmophiles - live in solutions with high solute
concentration (e.g. sugar content in jams)
Halophiles - requires high salt concentrations and
withstands hypertonic conditions
Ex. Halobacterium sp. (Archaea)
Facultative halophiles - can survive high salt
conditions but is not required for survival
Ex. Staphylococcus aureus
36
Other Factors
Radiation- withstand UV, infrared rays
Barophiles – withstand high pressures
Spores and cysts- can survive dry
habitats
37
Microbial Interactions
Influence microorganisms have on other
microbes:
Symbiotic relationship
Non-symbiotic relationship
38
Symbiotic Relationship
Organisms that live together in close nutritional
relationships
Types:
 Mutualism – both organism benefit
 Commensalism – only one organisms benefits
 Parasitism – typically host-microbe relationship
39
Commensalism
 “Satellitism”
as a form of
commensalism
 Staphylococcus
aureus provides
vitamins and amino
acids to Haemophilus
influenzae, which
grows around
colonies of S. aureus.
40
Non-Symbiotic Relationships
 Organisms are free-living, and do not
rely on each other for survival
 Types:
 Synergism – shared metabolism
enhances growth of both microbes
 Antagonism- competition between
microorganisms
41
Microbe-Host Interactions
Can be commensal, parasitic, and
synergistic
Ex. E. coli produce vitamin K for the host
42
Microbial Growth
 Binary fission
 Generation time
 Growth curve
 Enumeration of bacteria
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Binary Fission
Parent cell enlarges and duplicates its
DNA
Septum formation divides the cell into two
separate chambers
Complete division results in two identical
daughter cells
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Steps in Binary Fission
Rod-shaped bacteria undergoing binary fission
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Growth Curve
Lag phase
Log phase
Stationary phase
Death phase
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Phases of Bacterial Growth
Growth curve in a bacterial culture.
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Enumeration of Bacteria
 Direct Methods:
(a) Microscopic
(b) Viable plate count
(c) Membrane filtration
(d) Most probable number
 Indirect Methods:
(a) Turbidity
(b) Metabolic assay
(c) Dry weight determinations
48
Direct Microscopic Count
The direct cell method counts the total dead and live cells
in a special microscopic slide containing a premeasured grid.
Petroff-Hausser counting chamber used in dairy industry.
49
Standard Plate Count
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
Serially diluted samples are plated out and bacterial count expressed in CFU/ml.
50
Membrane Filtration
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this picture.
QuickTime™ and a
TIFF (Uncompressed) decompressor
are needed to see this pi cture.
Membrane filtration and coliform counts.
51
Turbidimetric
Turbidimetric measurements as indicators of bacterial growth.
The greater the turbidity the larger the population density.
52
Coulter Counter
The Coulter Counter
uses an electronic
sensor to detect and
count the number of
cells.
Rapid automated
counting method
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