Review on Bacterial Cell Division and Growth Rates

Read this article to larn about the growth and cell cycle of a leaner!

Growth of Bacteria:

When a prokaryote cell is inoculated into (placed on or in) medium, containing all the essential ingredients for growth, the cell volition: accumulate nutrients; synthesize new cell constituents; grow in size; replicate its genetic material; lay downward new prison cell wall; and, eventually, dissever in ii.

Consequently one cell becomes ii so, after another menstruum of fourth dimension, these split up to become four. This type of cell partition is called binary fission and this blazon of doubling growth is called exponential growth.

A population of prokaryotes growing in, this way will double in number during a detail length of fourth dimension called the generation or doubling time.

Generation time (g) = fourth dimension (t)/number of generations (n)

The number of generations tin can exist calculated, if the original (N₀) and final number (North) of cells is known, using the formula n = 3.three (log N – log N₀)

The rate at which a population grows (the number of generations per unit time) is expressed as hateful, or specific growth charge per unit abiding, and this is measured using the post-obit equation:

Hateful growth rate (μ) = 0.69/ thousand

From this formula it can be seen that as the specific growth rate increases, the generation fourth dimension will decrease.

The charge per unit at which bacteria grow and divide depends on the nature of the microbe, the ingredients of the medium in which it is grown, and the environmental conditions. For example, E. coli, when grown in a rich medium, with plenty of aeration at 37°C is capable of dividing every 20 min.

This rate of cell, division decreases if the prokaryotes are placed in a minimal medium where they are required to synthesize essential macromolecular precursors such as amino acids and bases. In contrast, Mycobacterium tuberculosis has a maximum doubling time of about eighteen h and will take much longer than East. coli, for example, to form colonies on an agar plate.

Bacterial Cell Cycle:

The sequence of events extending from the formation of a new cell to the side by side division is chosen the jail cell bicycle. In this cycle, an E. coli cell will grow in length, with trivial change in diameter, until it reaches a 'critical size, twice a unit cell length.

Jail cell sectionalisation is initiated: a contractile band is formed in the centre of the jail cell, septation proteins synthesize new jail cell wall and two new cells are formed, each ane containing at least ane re-create of the bacterial DNA. Consequently, during this time, a copy of the chromosome must be synthesized and the two, chromosomes segregated into the ii progeny cells.

Deoxyribonucleic acid replication occurs during the C (chromosome replication) phase and chromosome segregation occurs in the M (gap) phase, which may be of variable length. The mechanism by which chromosomes segregate is still unclear. Finally, across wall (septum) is laid down between the 2 chromosomes and the cell divides into ii (D stage). Jail cell division and Dna replication have to be coordinated.

Initiation of Deoxyribonucleic acid replication at the origin (oriC), a brusque adenine and thymine rich sequence, is dependent on the cell reaching a critical mass (initiation mass) and requires a number of poly peptide initiation factors.

DNA segregation and division, however, are controlled by the length of the cell which must reach a particular threshold length before the chromosomes are partitioned and cell segmentation initiated. A multitude of cellular and environmental factors control the process.

Rapid Growth:

When atmospheric condition for growth are favourable, E. coli tin grow with a' generation time of approximately xx min. However, the time it takes to synthesize a complete re-create of the E. coli chromosome is 40 min, under optimum conditions, and segregation of the Deoxyribonucleic acid and sectionalization takes another 20 min.

Thus, the shortest jail cell cycle and, therefore, generation time for Due east. coli should be 60 min. This is obviously not the instance. For cells to divide faster than every 60 min, DNA replication must begin in one cycle and finish in another

When cells are growing quickly (generation time < 60 min), initiation of replication occurs, as normal, producing two replication forks which movement bidirectionally round the chromosome to the termination point.

However, the origins on these new strands then initiate farther rounds of replication before the previous round of DNA replication has finished. Thus, when cell sectionalisation occurs the DNA in the daughter cells is already replicating. The faster the cell growth rate, the more replication forks are formed such that the DNA in new cells may have multiple replication forks.

Growth in Batch Culture:

The best manner of producing large numbers of microbes is to grow them in a liquid medium the technique we used is called batch culture in which the cells are inoculated into flasks of a suitable medium and grown at an advisable temperature and caste of aeration. Prokaryotes grown in this way show a particular pattern of growth referred to equally the bacterial growth curve.

The number of viable bacterial cells is measured over time and is plotted as a graph of the log₁₀ viable jail cell numbers against time. This is called a semi-logarithmic plot. A logarithmic scale is used to plot prokaryote growth owing to the big numbers of cells produced and to reveal the exponential nature of microbial growth.

If an arithmetic calibration is used to plot the 'increment in the number of cells, a curve of increasing gradient would be seen. This is converted into a straight line when a logarithmic scale is used. The generation time for the prokaryote tin can be read straight from the graph. The prokaryote growth curve reveals four phases of growth.

i. Lag stage:

When bacteria are outset inoculated into a medium in that location is a period in which no growth occurs. During this phase the cells are adapting to the new environment, synthesizing new enzymes as required and increasing jail cell size ready for cell partitioning.

The length of this fourth dimension depends on the nature of the inoculum. If this comes from a fresh culture in the same medium, the lag phase will be short, just if the inoculum is old or the medium has been changed (specially moving bacteria from a rich medium to a poor one) the lag phase will be longer.

ii. Exponential (logarithmic) phase:

Once the prokaryotes showtime to split up, the numbers increase at a constant rate which reflects the generation (doubling) time of the prokaryote. This is seen every bit a straight line in this role of the graph.

3. Stationary phase:

Equally the prokaryotes increment in numbers they employ up all the bachelor nutrients and' accrue growth inhibitors. Eventually a point is reached where in that location is no net increase in cell numbers, seen equally a flattening-off of the growth bend. During this state of equilibrium, cells are still functioning. At that place is some jail cell death which is counterbalanced by some pocket-sized amounts of controlled cell partition.

iv. Death phase:

After a while the charge per unit of cell death becomes greater than cell segmentation and the number of viable cells drops. Cells lyse and the culture becomes less turbid.

Lock et al. (1965) has proposed unlike terminology for these growth stages. They used 'tropophase' for the log stage and 'idiophase' for the stationary phase of batch civilization. This typical growth curve is known as 'sigmoidal growth curve'.

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Source: https://www.yourarticlelibrary.com/biology/bacteria-growth-and-cell-cycle-of-bacteria/22993

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