uses of Growth curve


what is Growth curve? what are the uses of Growth curve? types of Growth curve?

lag phase:-

the addition of inoculum to a new medium is not followed immediately by doubling of population.

the population remains results temporary unchanged.

during this page the individual cell increase in size beyond their normal dimensions.

at the end of the lab phase each organism divides.

Logarthamic {or} expotential phases:-

during this period the cells divide steadily at a constant rate and the lag of the number of cell plotted against time results in a straight line

the generation time {g} {the time required for the population doubled} can be determined from the number of generation {n} that occur in a particular time interval {t}.

The generation time is not the same for a particular species under all conditions. it is strongly dependent upon the nutrients in the medium.

during expontential growth, the growth rate termed {R} is the reciprocal of the generation time {g}

Stationary phases:-

the logarthamic  phase of growth begins to trapper of several hurts. these Trends towards cessation of growth can be attributed to a variety of circumstances particular deexhaustion of some nutrients and less often,and the production of toxic products during growth

the population remains constant for a time perphase as a result of complete cessation of division {or} perhaps because the reproduction rate is balance by equivalent death rate.

phase of decline:-

 following the stationary phase the bacteria may die then new cells are produced.

 in this deplication of essential nutrients and accumulation of inhibitory products, such as acid during the death phase, the number of viable cells decreases expotentially.

bacteria die at different rates

synchronous growth:-

 There are several laboratory techniques by which we can manipulate the growth of culture so that all the cells will be the same stage of their growth cycle that is growing synchronously.

The synchrony generally lasts only a few generation’s since even daughters of the single cell. get out of phase with one another.

a population can be synchronised by manipulating the physical environment {or} chemical composition of the medium.


 the cell maybe inoculated into a medium at A sub-optimal temperature

When the temperature is subsequently raised the cell will undergo a synchronised division.

the most common method of synchronisation takes advantage of the fact that the smallest cell in Log Phase culture are those which have just divided.

 when these cells are separated out by filtration {or} by differential centrifugation, they are reasonably well synchronised with each other.

continuous growth:-

the culture volume and the cell concentration are both kept constant by allowing free sterile medium to enter the culture at the same rate that spent medium, containing cell is removed from the growth culture. 


one type of system that is widely employed for continuous cultivation is the chemostat

the system depends on concentration of an essential nutrient within the culture vessel will control the growth rate of the cell.

the concentration of the substance within culture vision is in the turn controlled by the dilution rate that is the rate at which fresh medium is begin added to the culture divided by the volume of the culture medium vessel.

therefore by adjusting the dilution rate we can control the growth rate.


this is the second type of continuous culture Apparatus.

here a photoelectric device continuously monitor the cell  density within the culture vessel and control the dilution rate to maintain the cell density at a constant volume

 if the density becomes too high The dilution rate is increased if the density becomes too low The dilution rate is decreased

measurement of growth:-

 growth rate refers to the total population growth rate can be determined by numerous techniques based on one {or} more of the following of measurements

cell count:-

directly by microscopy {or} by using an electronic particle counter {or} indirectly cell count.

Cell mass:-

directly by weighing {or} by a turbidity.

cell activity:-

 indirectly by a relating the degree of biochemical activity to the size of pollution.

direct microscopic count:-

 bacteria can be counted easily and accurately with the petroff hausser counting chamber

 a suspension of unstained bacteria can be counted in a chamber using a phase contrast microscope.

determination of nitrogen:-

the major constituent of the cell material is protein and since nitrogen is a characteristic part of protein one can measure a bacterial population

 bacteria average percentage 14% nitrogen on a dry weight basis.

 to measure growth by this technique you must first harvest the cell and wash them free of medium and then perform a quantitative chemical analysis for nitrogen.

 this method is applicable only for concentrated population. 

determination of the dry weight of cells:-

this is most direct approach for quantitative measurement of a mass of cells.

 it can be use only with very dense suspensions and the cell must be washed free of all extraneous matter.

Dry weight may not always indicative of the amount of living materials in cells.


intracellular reverse material poly β-hydroxy buterate can accumulate in azotobacter, beiijerinckii  by the end of Log Phase of growth and during the stationary phase and finally can compromise up to 74% of dry weight of the cell.

 inactivation temperature:-

to select for psychrophilic culture are incubated at low temperature at 00-5oc.

for selection of thermophiles, a high incubation temperature is used that have 550c.

ph:- to select for Acid tolerant bacteria a low pH medium can be used. to select for the lactobacilli the pH of the medium is maintained at 5.35 with acetic acid.

To select for alkalic tolerant organisms a high ph medium can be used. to select for The cholera-causing bacterium, vibrio Cholera, we can use medium with a ph 8.5.

Pure culture:-

 the descendants of a single isolation in pure culture comprise a strain.

a strain is as usually made up of a succession of cultures and is often derived from a single Colony.

 if a strain is derived from a single parent cell, it is termed as clone.

a variety of techniques have been developed where by isolation in to pure culture can be accomplished.

 methods of isolating pure culture:-

 streak-plate technique:-

by means of transfer loop, a portion of the mixed culture is placed on the surface of an Agar medium and streaked across the surface.

this manipulation “thins out” the bacteria on the agar surface so that some individual bacteria are separated from each other.

A nutrient Agar plate culture that has been streaked to provide isolated colonies.

when streaking is properly performed the bacterial cell will be sufficient for apart in some areas of the plate.

to ensure that the colony developing from one cell will not merge with that growing from another.

Pour plate technique:–

The mixed culture is first diluted to provide only a few cells per milli liter before being used to inoculate Media.

a series of dilutions is made so that atleast one of the dilutions will contain a suitably sparse concentration of cells.

In pour plate method, the mixed culture is diluted directly in tubes of liquid {cooled}, Agar medium.

the medium is maintained in a liquid state at room temperature of 450c to allow through distribution of the inoculums.

the inoculated medium is dispensed into Petridish allowing the solidify and then incubated.

a series of agar plates showing decreasing number of colonies, resulting from the dilution procedure in the pour plate technique.

the pour plate technique has certain disadvantages. for instance, some of the organisms are trapped beneath the surface of the medium when it gets and therefore both surface and subsurface colonies develop. 

spread plate technique :-

in the spread plate method the mixed culture is not diluted in the culture medium instead it is diluted in a series of tubes containing is sterile liquid.

A sample is removed from each tube placed on the surface of an Agar plate and spread evenly over the surface by means of sterile bent glass rod.

Methods of maintenance and preservation:-

Strains can be maintained by periodically prepairing a fresh stock culture from the previous stock culture.

the culture medium the storage temperature and the time interval at which the transfers are made vary with the species and must be ascertained.

preservation by overlying cultures with mineral:-

many bacteria can be successfully preserved by covering the growth on an agar slant with sterile Mineral oil.

The oil must cover the slant completely to ensure this The oil should be about  ½  in the above the tip of the slanted surface.

preservation by lyophilization:-

most of the bacteria die if cultures are allowed to become dry,although spore and cyst forms remain for many years.

Freeze-drying Can satisfactorily preserve many kinds of bacteria that would be killed by ordinary drying.

in this process a dense cell suspension is placed in small vials and frozen at -60 to -780c.

the vials are connected to a high vacuum.

the ice present in the frozen suspension under the vacuum that have evaporated without first going though a liquid water phase.

this result in dehydration of the bacteria with a minimum of damage to delicate cell structures.

the vials are Then seated off Under a vacuum and stored in refrigerator.

storage at low temperature:-

the Ready availability of liquid nitrogen is used for long term preservation of culture.

in this method cells are prepared as a dense suspension in a medium containing a cryopreservation agent such as glycerol which prevents cell damage due to Ice crystal formation during the subsequent steps. the cell suspension is sealed into small vials and then frozen at a controlled rate to 1500c.

the ampouls {or} vials then stored in a liquid nitrogen refrigerator

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