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Bacterial Physiology
By
Dr.
Zubaida Najat Mustafa
MICROBIAL GROWTH:
Refers to an increase in cell number, not in cell
size.
Bacteria grow and divide by binary fission,a
rapid and relatively simple process.
In which parent cell divides to form a progeny
of two cells
Microbial Growth
MICROBIAL GROWTH
Requirements for Growth
Physical Requirements
1. Temperature:
Microbes are loosely classified into several groups based on their
preferred temperature ranges.
A. Psychrophiles: “Cold-loving”. Can grow at
Two groups:
1-TEMPERTURE
A-PSYCHROPHILES:
True Psychrophiles: Sensitive to temperatures
1over20˚.
Optimum growth at 15C ˚ or below. Found in very cold environments
(North pole, ocean depths).
Seldom cause disease or food spoilage.
Psychrotrophs: Optimum growth at 20 to 30C˚.
Responsible for most low temperature food spoilage.
1- TEMPERTURE
B. MESOPHILES
Mesophiles: “Middle loving”. Most bacteria.
Include most pathogens and common spoilage
organisms.
Best growth between 25 to 40oC.
Optimum temperature commonly 37oC.
Many have adapted to live in the bodies of animals
1. TEMPERATURE:
C. THERMOPHILE
C. Thermophiles: “Heat loving”.
Optimum growth between 50 to 60oC.
Many cannot grow below 45oC.
Adapted to live in sunlit soil, compost piles, and hot springs.
Some thermophiles form extremely heat resistant
endospores.
1. TEMPERATURE:
C. THERMOPHILE
Extreme Thermophiles (Hyperthermophiles):
Optimum growth at 80oC or higher. Archaebacteria. Most live in
volcanic and ocean vent
REQUIREMENTS FOR GROWTH
PHYSICAL REQUIREMENTS
2. PH:
Most bacteria prefer neutral pH (6.5-7.5).
Acidity inhibits most microbial growth and is
used frequently for food preservation (e.g.:
pickling).
Alkalinity inhibits microbial growth, but not
commonly used for food preservation.
Acidic products of bacterial metabolism
interfere with growth
REQUIREMENTS FOR GROWTH
PHYSICAL REQUIREMENTS
2. PH
Organisms can be classified as:
A. Acidophiles: “Acid loving”. Grow at very low pH (0.1 to 5.4) example
Lactobacillus produces lactic acid
B. Neutrophiles: Grow at pH 5.4 to 8.5. u Includes most human
pathogens.
C. Alkaliphiles: “Alkali loving”. Grow at alkaline or high pH (7 to 12 or
higher) example Vibrio cholerae and Alkaligenes faecalis optimal pH 9.
REQUIREMENTS FOR GROWTH
PHYSICAL REQUIREMENTS
3. OSMOTIC PRESSURE
Cells are 80 to 90% water..
Hypertonic solutions: High osmotic pressure
removes water from cell, causing shrinkage of cell
membrane (plasmolysis). Used to control spoilage
and microbial growth. Sugar in jelly. u Salt on meat.
B. Hypotonic solutions: Low osmotic pressure
causes water to enter the cell. In most cases cell
wall prevents excessive entry of water.
Microbe may lyse or burst if cell wall is weak.
REQUIREMENTS FOR GROWTH
PHYSICAL REQUIREMENTS
3. OSMOTIC PRESSURE
Halophiles: Require moderate to large salt
concentrations. Ocean water contains 3.5% salt. Most
bacteria in oceans. Extreme or Obligate Halophiles:
Require very high salt concentrations (20 to 30%). u
Bacteria in Dead Sea, brine vats
Facultative Halophiles: Do not require high salt
concentrations for growth, but tolerate 2% salt or more.
REQUIREMENTS FOR
GROWTH CHEMICAL
1. Carbon: Makes up 50% of dry weight of cell. Structural
backbone of all organic compounds.
Bacteria obtained carbon in two maine way:Heterotrophs: Obtain carbon from their energy source: lipids,
proteins, and carbohydrates.
Autotrophs and Photoautotrophs: free living Obtain carbon
from carbon dioxide.
REQUIREMENTS FOR GROWTH
CHEMICAL REQUIREMENTS 2.
NITROGEN, SULFUR, AND
PHOSPHORU
A. Nitrogen: Makes up 14% of dry cell weight. Used to
form amino acids, DNA, and RNA. Sources of nitrogen:
Protein: Found in organic matter u Nitrogen gas (N 2 ):
Obtain N directly from atmosphere. Important nitrogen
fixing bacteria, live free in soil or associated with
legumes (peas, beans, alfalfa, clover, etc.). Legume
cultivation is used to fertilize soil
REQUIREMENTS FOR GROWTH
CHEMICAL REQUIREMENTS 2.
NITROGEN, SULFUR, AND
PHOSPHORUS
Used to form proteins and some vitamins (thiamin and
biotin).
Sources of sulfur: Protein
: Most bacteria Hydrogen sulfide u Sulfates: Salts that
dissociate to give SO 4
Phosphorus: Used to form DNA, RNA, ATP, and
phospholipids. Sources: Mainly inorganic phosphate salts
and buffers.
REQUIREMENTS FOR GROWTH
CHEMICAL REQUIREMENTS
OTHER ELEMENTS:
Potassium, magnesium, and calcium are often required
as enzyme cofactors.
Calcium is required for cell wall synthesis in Gram
positive bacteria.
. Trace Elements:. Many are used as enzyme cofactors
. Usually metals needed in very little amount but are
critical to cell function
e.g. Nickel(Ni), selenium (Se), Tungsten ( W), copper
(Cu), Cobalt (Co).
Organic Growth Factors
Organic compounds obtained from the
environment and needed in very small amount
only by some cells
Vitamins, amino acids, purines, pyrimidines
REQUIREMENTS FOR GROWTH
CHEMICAL REQUIREMENTS
OXYGEN
A. Obligate Aerobes: Require oxygen to live.
B. Facultative Anaerobes: Can use oxygen, but can
grow in its absence. Have complex set of enzymes.
Examples: E. coli, Staphylococcus, yeasts, and
many intestinal bacteria.
C. Obligate Anaerobes: Cannot use oxygen and are
harmed by the presence of toxic forms of oxygen.
Examples: Clostridium bacteria that cause tetanus
and botulism.
Toxic Forms of Oxygen
• Utilization of O2 during metabolism yields toxic byproducts including singlet oxygen:(1O2), superoxide free
radicals (O2), hydrogen peroxide (H2O2) and Hydroxyl
radical(OH).
• Toxic O2 products can be converted to harmless
substances if the organism has catalase (or peroxidase)
and
superoxide
dismutase
(SOD)
enzymes.
ANAEROBIC CULTURE METHODS
Candle jar
CO2-packe
CAPNOPHILES REQUIRE HIGH
CO2
MICROBIAL GROWTH
CULTURE MEDIA
CULTURE MEDIUM
-Culture Medium: Medium containing nutrients
that support microbial growth
-Sterile: No living microbes
-Inoculum: Introduction of microbes into medium
-Culture: Microbes growing in/on culture medium
Types of Culture Media
Enrichment Culture
Special media
Differential Media
Nutrient media
Selective Media
Selective and Differential Media
MICROBIAL GROWTH PHASES
OF GROWTH BACTERIAL
GROWTH CURVE:
When bacteria are inoculated into a liquid
growth medium, it regulated by nutritional
environment . Four phases of Bacterial
Growth:
1. LAG PHASE
a- Period of adjustment to new conditions.
b- Little or
increase.
no cell division occurs, population size doesn’t
C- May last from one hour to several days
2- LOG PHASE:
Cells begin to divide and generation time reaches a constant
minimum.
Period of most rapid
growth.
Number of cells produced
>
Number of cells dying
Cells are at highest metabolic activity.
Cells are most susceptible to Antibiotics
3- STATIONARY
PHASE
Population size begins to stabilize.
Number of cells produced = Number
of cells dying
Overall cell number does not
increase.
Cell division begins to slow down.
Note/
Factors that slow down microbial
growth: Accumulation of toxic waste
materials Acidic pH of media Limited
nutrients Insufficient oxygen supply
(Growth rate = death rate)
4- DEATH OR DECLINE PHASE
Population size begins to decrease.
Number of cells dying>Number of cells produced
Cell number decreases at a logarithmic rate.
Cells lose their ability to divide.
A few cells may remain alive for a long period of
time
death rate is greater than growth rate
BACTERIAL GENETICS
Genetics is the study of inheritance and variation. All inherited
characteristics are encoded in DNA,
except in RNA viruses
The bacterial chromosome
The bacterial chromosome contains the genetic information that defines
all the characteristics of the organism.
It is a single, continuous strand of DNA with a closed, circular structure
attached to the cell membrane of the organism.
REPLICATION
Chromosome replication is an accurate process that ensures
that the progeny cells receive identical copies from the
mother cell. The replication process is initiated at a specifc
site on the chromosome(oriC site ) where the two DNA are
locally denaturated
GENETIC VARIATION IN
BACTERIA
can occur as a result of mutation or gene transfer.
1- Mutation
A mutation is a change in the base sequence of DNA, as aconsequence
of which different amino acids are incorporated into a protein, resulting
in an altered phenotype.
A- Frame shift
B- Insertion
GENE
TRANSFER:RECOMBINAT
ION
The transfer of genetic information can occur by:
A-conjugation
B- transduction
C- transformation
D- transposition
The result is a recombinant cell that has a genome different from
either the donar or the recipient.
CONJUGATION IN E.COLI
IS THE PROCESS BY WHICH BACTERIA TRANSFER GENES
FROM ONE CELL (DONOR-MALE ) TO THE RECEPIENT(FEMALE) BY CELL
TO CELL CONTACT
Transformation:-
Is the process a free double stranded DNA enters the recepient cell .
One of the two strand destroy by cell nuclease , the remaing single
strand invade the resident chormosome seeking a homologous
sequence
Transduction by a Bacteriophage
Is the process transferring of gene from one cell
to another Via a Phage without cell to cell contact
TRANSPOSONS
Transposons, also called jumping genes, are pieces of DNA
that move readily from one site to another, either within or
between the DNAs of bacteria, plasmids and bacteriophages.
In this manner, plasmid genes can become part of the
chromosomal complement of genes
PLASMIDE
Plasmids are extrachromosomal
double-stranded circular DNA molecules .
They are capable of replicating independently of the
bacterial chromosome i.e. they are (replicons).
Plasmids occur in both Gram-positive and Gramnegative bacteria, and several different
plasmids can often coexist in one cell.
PLASMIDS
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