Lesson 9: PRINCIPLES OF BACTERIAL GROWTH Flashcards
refers to increase in number of cells and not the
size of cells.
Bacterial/microbial growth
the bacteria undergo asexual cell division to produce two daughter cells genetically identical to the parent cell. These two daughter cells produce four, then eight and so on.
Binary fission
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 hours.
Generation time
Binary fission subsequent events
- begins with DNA replication and segregation of nucleoids (distribution between the future daughter cells)
2 a Z-ring composed mainly of FtsZ polymers is assembled in the middle of the cell. - the Z-ring recruits additional proteins that serve for septum formation and subsequent separation of the daughter cells.
Generation time of E. coli
20 minutes
In 7 hours 20 generation
1 million cells
And in 24 hours 10^21 cells
until arrested
Microbial concentrations can be measured in terms of
Cell concentration or biomass concentration
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
denotes the total number of bacteria in the sample, irrespective of whether they are living or dead. This is done by counting the bacteria under the microscope using counting chamber or by comparing the growth with standard opacity tube
Total counts
indicates the number of living or viable bacteria.
Viable count
Viable count can be obtain by
Dilution method or plating method
series of sequential dilutions used to reduce a dense culture of cells to a more usable concentration
Dilution method
Four phases of growth curve
- Lag phase
- Log phase
- Stationary phase
- decline phase
number of colonies that grow after a suitable incubation time
Plating method
The time between inoculation and beginning of multiplication. In this phase, the inoculated bacteria become acclimatized to the environment, switch on various enzymes, and adjust to the environmental temperature and atmospheric conditions. During this phase, there is an increase in size of bacteria but no appreciable increase in number of bacterial cells. The cells are active metabolically.
Lag phase
represents the number of live cells in a bacterial
population over a period of time.
The bacterial growth curve
This phase is characterized by rapid exponential cell growth of bacteria at their maximum rate. The bacterial cells are small and uniformly stained. The microbes are sensitive to adverse conditions, such as antibiotics and other antimicrobial agents.
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). Death rate of bacteria exceeds the rate of replication of bacteria. Endospores start forming during this stage
Stationary phase
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
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. Involution forms are common in this stag
Decline phase
The Bacterial Physical requirements are
Temperature
pH
Osmotic Pressure
Requirements of bacterial growth
Physical requirements
chemical requirements
The bacterial chemical requirements are
Carbon
Nitrogen
sulfur
Phosphorus
trace elements
oxygen
organic growth factors
