BACTERIAL GROWTH CURVE

 

BACTERIAL GROWTH CURVE

MEANING OF GROWTH:

GROWTH means as we all know INCREASE.

SO, hear  we speak about GROWTH OF BACTERIA but in DIFFERENT STAGES.

GROWTH is the orderly increase in the sum of all the components of an organism. The increase in size that results when a cell takes up water or deposits lipid(fats) or polysaccharide is not true growth.

CELL MULTIPLICATION is a consequence of cell division of unicellular organisms, growth leads to an increase in the number of single bacteria making up  a population, referred to as a culture.

Measurement of microbial concentrations:

 

These concentrations can be measured in terms of cell concentration(the number of viable cells per unit volume of culture) or of biomass concentration (dry weight of cells per unit volume of culture).

 

CELL CONCENTRATION:

The viable cell count is considered the measure of cell concentration. The Turbidity of cell concentration, measured by photoelectric means , is related to the viable count in the form of STANDARD CURVE.

 

BIOMASS DENSITY:

 

Biomass can be measured directly by determining the dry weight of a microbial culture after it has been washed with distilled water.

The concentration of biomass can be estimated indirectly by measuring n important cellular component such as protein or by determining the volume occupied by cells that have settled out of suspension.

 

PHASE	GROWTH RATE
LAG	ZERO
EXPONENTIAL	CONSTANT
STATIONARY	ZERO
DECLINE	NEGATIVE(DEATH)

 

GROWTH CURVE:

IT is a fixed volume of liquid medium is inoculated with microbial cells taken from a culture that has previously been grown to saturation and the number of viable cells per millilitre is determined periodically.

The phases of the bacterial growth curve are reflected of the events in a population of cells. This type of culture is known as BATCH CULTURE.

The growth curve may be discussed in terms of four phases.

LAG PHASE:

It is a period where the individual bacteria are maturing and not yet able to divide, during lag phase of the bacterial growth cycle, synthesize of RNA, enzymes and other molecules.

Some easy key points :

·       No appreciable increase in number but there is INCREASE IN SIZE OF THE CELLS.

·       Accumulation of enzymes and metabolic intermediates.

·       MAXIMUM CELL  SIZE is obtained at the end of lag phase.

LOG PHASE:

THE log phase (sometimes called the logarithmic phase or exponential phase) it is characterized by cell doubling. Number of new bacteria appearing per unit time is proportional to the present population.

Some key points:

·       also called as EXPONENTIAL PHASE.

·       Number of cells increase exponentially

·       Cells are small and stain uniformly

·       Increase in metabolic rate.

 

 

 STATIONARY PHASE:

THE rate of bacterial cell growth is equal to the rate of bacterial cell death. The size of population of bacteria remains constant, even though some cells continue to divide and others begin to die.

 

Some key points:

·        an equilibrium exists between dying cells and newly formed cells

·        Cells are viable and show IRREGULAR STAINING due to intracellular storage granules.

·        SPORULATION OCCURS AT THIS STAGE.

·        Production of  antibiotics and exotoxins.

 

DECLINE PHASE:

DEATH of bacteria due to lack of nutrients, environmental temperature above or below the tolerance band for species or other injurious  conditions.

·       POPULATION  of cells DECREASES DUE TO CELL DEATH.

·       INVOLUTION FORMS ARE COMMON.

      we will meet again with another topic....

By

 Dr.Sneha