Synchronous culture is a technique of growing microorganisms at the same stage of their growth cycle in the controlled conditions. The results are made by one of the two methods (forced or mechanical selection methods). Forced techniques induce synchrony in microorganisms by shock treatment (temperature variation) or chemical treatment (nutritional difference).
In contrast, the mechanical method makes the use of filtration or centrifugation techniques to collect the cells having same age and size. The microbial population in synchronous culture never lasts more than 4-5 generations, as the generation time for individual dividing cells varies considerably.
Contents: Synchronous Culture
Definition of Synchronous Culture
Synchronous culture can define as the growth process of the microbial population, where the individual cells show synchrony with the other cells in the culture medium by growing at the same growth phase for the given generation time.
The main characteristic of synchronous growth is that all the microbial cells are physiologically identical by growing at the same division cycle at the same time. Therefore, we can say that the entire microbial population remains uniform concerning cell growth and division.
By using synchronous culture, we can get the idea of the entire cell crop in the particular stage of their life cycle and their interrelations. The measurement of microbial growth is quite more accessible than the other growth culture techniques, as the results made on such mass culture is analogous to the measurements made on a single bacterial cell. In the synchronous culture, we can elucidate the growth behaviour of the bacterial cell in the same stage of growth.
- The entire microbial population tends to show synchrony by altering the physical conditions and chemical constituents of the culture media.
- It is a kind of open cultivation system.
- In synchronous culture, the microbial cells are physiologically similar.
- All the microbial cells in synchronous culture grow for the same generation time in the same divisional cycle.
The Efficiency of Synchronous Culture
The bacterial cells show asynchronous growth in the random culture medium. However, the microbial cells show synchrony by the selection and induction methods, and its efficiency can be evaluated by comparing with the following parameters like:
- The mitotic index
- Generation time for doubling the microbial population
We can understand the growth pattern of cells by plotting a graph between doubling time vs a logarithmic number of cells and by corresponding mitotic indices for a synchronous and random culture.
Selection of microorganisms
Selection by Mechanical Method
It can define as a physical separation method, where the selection of the synchronous population is carried out according to the age and size. In this method, the microbial cells are first filtered out to separate the small-cells, which are metabolically active and the youngest cells that these must go through their whole life cycle before dividing.
The large-cells will retain by a filter, which is ready to split. Therefore the large-cells are collected from the filter to obtain a synchronous growth by a standard technique refers as “Helmstetter Cumming technique”.
In this method, the entire cell population is passed through a filter whose particle size is small sufficient to trap the bacteria. This method makes the use of cellulose nitrate membrane filter. Then the filter paper is inverted, over which the fresh nutrient medium is allowed to flow.
By doing this, the loosely associated bacteria are washed away through the filter. The large-sized bacteria will remain on the filter paper and tend to divide. The sample of this stream is collected, where all the cells are newly formed, which will divide synchronously.
This method has one disadvantage that the population size is petite. Nowadays, instead of filtration, density gradient centrifugation is also used for the selection of microbial cells of the same size and density, which can divide at the same stage of their life cycle.
Selection by Induction Method
Synchrony can also be maintained by employing shock treatment including temperature variation, starvation, light exposure, lethal doses of radiation etc. All the above factors can maintain synchrony in the cell population for several generations.
Temperature variation is the most common factor that induces the cell maturation to the same point of fission. A microbial culture growing under 37 degrees Celsius is taken and then kept at 20 degrees Celsius for about 30 minutes.
During this interval, the cells go through maturation to undergo cell division. At 20 degrees Celsius temperature, no bacteria will undergo fission. But, when the culture is again kept at a temperature of 37 degrees Celsius, all the cells start dividing synchronously. Therefore, the synchrony can be maintained only for a few generations by repeated temperature variation.
Other than shock treatment, the induction method also involves alternations in the media composition of the culture medium. If the microorganisms grown in the culture medium that is deficient or containing the growth factor required or inhibited the cell division results to withheld the fission.
Suppose the bacterial cells are grown in a culture medium that lacks thymine, which is an essential element that will halt the process of fission for some time. However, the bacterial cells will divide when cultured in a complete nutrient medium. Colchicine is a growth factor that inhibits the cell division in culture medium for a certain period. But the effect can be reversed when the cells are transferred to the culture medium free of colchicine.
Therefore, we can conclude that the synchronous culture are of two kinds, namely induction and selection synchrony. The induction synchrony induces cell population to undergo fission synchronously via physical or chemical treatment. Oppositely, the selection synchrony selects cells at a particular stage of the cycle, and later the fractions of bacterial cells grow through their natural cycle.