LESSON 9: BATERIAL GROWTH Flashcards
refers to increase in number of cells and not the size of cells.
Bacterial growth
in which the bacteria undergo
asexual cell division to produce two daughter cells genetically identical to the parent cell.
Binary fission
Begins with DNA replication and
segregation of nucleoids
(distribution between the future
daughter cells).
Cell division
the time required for a bacterium to give rise to two
daughter cells under optimum conditions. A bacterium replicates and multiplies rapidly producing millions of cells within 24
Generation time
Bacterial Concentration
(i) cell concentration
(the number of viable cells per unit volume of culture) or
(ii) biomass concentration
(dry weight of cells per unit volume of culture)
(i) cell concentration
(the number of viable cells per unit volume of culture) or (ii) biomass concentration
(dry weight of cells per unit volume of culture)
denotes the total number of bacteria in the sample, irrespective
of whether they are living or dead.
Total count
indicates the number of living or viable bacteria
Viable count
This count can
be obtained by dilution method (series of sequential dilutions used to reduce a dense
culture of cells to a more usable concentration) or plating method (number of
colonies that grow after a suitable incubation time).
FOUR PHASES OF GROWTH CURVE :
- Lag phase
- Log phase
- Stationary phase
- Decline phase
The time between inoculation and beginning of multiplication is
known as
Lag phase
This phase is characterized by rapid exponential cell growth of
bacteria at their maximum rate.
Log phase
After log phase, the bacterial growth almost stops
completely due to depletion of essential nutrients, water oxygen, change in pH
of the medium, etc. and accumulation of their own toxic metabolic wastes
(exotoxin
Death rate of bacteria exceeds the rate of replication of bacteria. Endospores start forming during this stage
the bacterial population declines due to death of cells due to
(a) accumulation of toxic products and autolytic enzymes and
(b) exhaustion of nutrients
is a method utilized for industrial and research purpose that
is achieved by using a special device for replenishing nutrients and removing
bacterial population continuously so that bacteria growth is not inhibited due to lack
of nutrients or due to accumulation of toxic bacterial metabolites
REQUIREMENT FOR GRWOTH BACTERIAL
- Physical requirement
- Chemical requirement
PHYSICAL REQUIREMENTS
- Temperature
- pH
- Osmotic pressure
most bacteria grow within a limited range of temperature, and the minimum and maximum temperatures are only 30°C apart.
Temperature
- Minimum temperature is the lowest
temperature at which a species will grow. - Optimum temperature is
when a species grow best. - Maximum temperature is the highest
temperature at which a species can grow.
They grow poorly beyond
the minimum and maximum temperature
refers to the alkalinity or acidity of a solution. Most bacteria grow
best near neutral pH (6.5 – 7.5).
pH
the pressure required to stop water/solution from
diffusing through a barrier by osmosis
Osmotic pressure
Microorganisms require water
for growth and are made up of
80-90%
when solution outside the cell has higher concentration of solutes than
inside the cell, water is diffused outside of cell and the cell shrinks.
Hypertonic environment:
: when solution outside the cell has lower concentration of
solutes than inside the cell, water is diffused inside of cell and the cell
swells.
Hypotonic
: when concentrations in two solutions are same, so cell
will neither swells nor shrinks.
Isotonic
: important for all organic compounds that make up a living cell;
consist half the dry weight of a typical bacterial cell.
Carbon
helps form the amino group in amino acids
Nitrogen
used to synthesize sulfur-containing amino acids and vitamins
Sulfur
important in synthesis of ATP, nucleic acids and
phospholipids of cell membranes
Phosphorus
minerals that are minimally required by microbes, and
are also essential in enzymatic reactions
Trace Elements
is required by aerobic microorganisms, it is toxic to anaerobic bacteria like Clostridium tetanus
Oxygen
Singlet oxygen: extremely reactive
ii. Superoxide free radicals: highly unstable, steals electron from
neighboring molecules thereby increasing free radicals
iii. Peroxide anion
iv. Hydroxyl radical: most reactive form of oxyge
are essential organic compounds that cannot
be synthesized by an organism thus must be obtained from the
environment. Ex: vitamins
Organic growth factor
