CHAPTER 2: Lesson 9: Principles of Bacterial Growth Flashcards
It refers to increase in number of cells and not the
size of cells.
Bacterial/microbial growth
Most bacteria divide by _________ in which the bacteria undergo
asexual cell division to produce two daughter cells genetically identical to the parent
cell.
binary fission
It begins with DNA replication and
segregation
of
nucleoids
(distribution between the future
daughter cells); next, a Z-ring
composed
mainly
of
FtsZ
polymers is assembled in the
middle of the cell. Finally, the Zring recruits additional proteins
that serve for septum formation
and subsequent separation of the
daughter cells.
Cell division
It is the time required for a bacterium to give rise to two
daughter cells under optimum conditions.
Generation time
generation time
for most of the pathogenic bacteria, such as E. coli, is about ________, in about ________ can undergo 20 generations and produce 1 million cells, and in ________
produces 10²¹ cells
20 minutes
7
hours
24 hours
Microbial concentrations can be measured in terms of the following:
(i) cell concentration
(ii) biomass concentration
It is the number of viable cells per unit volume of culture.
cell concentration
Dry weight of cells per unit volume of culture.
biomass concentration
The number of bacteria at a given time can be estimated by ___________.
performing a total
count or viable count
It denotes the total number of bacteria in the sample, irrespective
of whether they are living or dead.
Total count
This is done by counting the bacteria under the
microscope using counting chamber or by comparing the growth with standard
opacity tubes.
Total count
It 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).
Viable count
Series of sequential dilutions used to reduce a dense
culture of cells to a more usable concentration.
dilution method
number of
colonies that grow after a suitable incubation time
Plating method
It represents the number of live cells in a bacterial
population over a period of time.
bacterial growth curve
Four phases of growth curve
- Lag phase
- Log phase
- Stationary phase
- Decline phase
The time between inoculation and beginning of multiplication is
known.
Lag phase
In this phase, the inoculated bacteria become
acclimatized to the environment, switch on various enzymes, and adjust to the
environmental temperature and atmospheric conditions.
Lag phase
During this phase,
there is an increase in size of bacteria but no appreciable increase in number
of bacterial cells.
Lag phase
The cells are active metabolically.
Lag phase
This phase is characterized by rapid exponential cell growth of
bacteria at their maximum rate.
Log phase
The bacterial cells are small and uniformly
stained.
Log phase
The microbes are sensitive to adverse conditions, such as antibiotics
and other antimicrobial agents
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
(exotoxins).
Stationary phase
Death rate of bacteria exceeds the rate of replication of bacteria.
Stationary phase
Endospores start forming during this stage.
Stationary phase
accumulation of their own toxic metabolic wastes
exotoxins
in this phase, the bacterial population declines due to death
of cells due to (a) accumulation of toxic products and autolytic enzymes and
(b) exhaustion of nutrients.
Decline phase
Involution forms are common in this stage.
Decline phase
It 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.
Continuous culture
Requirements for bacterial growth
- Physical requirements
- Chemical requirements:
Physical requirements
a. Temperature
b. pH
c. Osmotic pressure
- Chemical requirements
a. Carbon
b. Nitrogen
c. Sulphur
d. Phosphorous
e. Trace elements
f. Oxygen
g. Organic growth factors
most bacteria grow within a limited range of temperature,
and the minimum and maximum temperatures are only ______ apart
Temperature
30°C
It is the lowest
temperature at which a species will grow.
Minimum temperature
It is
when a species grow best.
Optimum temperature
It is the highest
temperature at which a species can grow.
Maximum temperature
Bacteria grow poorly beyond
the _______ and ______________.
minimum and maximum temperature
It refers to the alkalinity or acidity of a solution.
pH
Most bacteria grow
best near ___________. Few grow in __________ and
help preserve some food (pickles, sauerkraut, cheese) by bacterial
fermentation.
neutral pH (6.5 – 7.5)
acidic pH (below 4)
The pressure required to stop water/solution from
diffusing through a barrier by osmosis. Microorganisms require water
for growth and are made up of _________ water. They often obtain
nutrients in _________ from surrounding water.
Osmotic pressure
solution
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
Osmotic pressure (Physical Requirements)
Hypertonic environment
Hypotonic
Isotonic
important for all organic compounds that make up a living cell;
consist half the dry weight of a typical bacterial cell
Carbon
It helps form the amino group in amino acids
Nitrogen
used to synthesize sulfur-containing amino acids and vitamins
Sulphur
It is important in synthesis of ATP, nucleic acids and
phospholipids of cell membranes
Phosphorous
minerals that are minimally required by microbes, and
are also essential in enzymatic reactions
Trace elements
It is required by aerobic microorganisms, it is toxic
to anaerobic bacteria like Clostridium tetanus.
Oxygen
Oxygen is toxic
to anaerobic bacteria like what?
Clostridium tetanus
List of toxic
form of oxygen:
i. Singlet oxygen
ii. Superoxide free radicals
iii. Peroxide anion
iv. Hydroxyl radical
extremely reactive
Singlet oxygen
highly unstable
Superoxide free radicals
steals electron from
neighboring molecules thereby increasing free radicals
Superoxide free radicals
most reactive form of oxygen
Hydroxyl radical
These are essential organic compounds that cannot be synthesized by an organism thus must be obtained from the
environment.
Organic growth factors
Example of Organic Growth Factors
vitamins
