Growth and genetics of bacteria

Growth cycle of bacteria

Bacteria are prokaryotic therefore the growth or the reproduction process of them is called binary fission. It is a method by which one parent cell divides to form two daughter cells. Thus bacterial growth is an exponential one.

The time taken to complete a one cycle (the doubling time) is varying with type of bacteria. Escherichia coli have the lowest doubling time, 20 minutes, whereas Mycobacterium tuberculosis takes more than 24 hours to complete a one cycle.

The bacterial growth cycle consists of three phases;

1. The lag phase
2. The log phase
3. the stationary phase

1. The lag phase

This is the first phase of the growth cycle in which vigorous metabolic activity occurs but cell does not divide.

2. The log phase

This is the second phase in which rapid cell division occurs. Most of the antibiotics are effective during the log phase of reproduction.

3. The stationary phase

During this phase growth becomes slower as the nutrients depletion or toxic collection.

Aerobic and anaerobic growth

There are some bacteria which need oxygen for the growth whereas other does not need oxygen for the growth. There is another interesting group and they can utilize oxygen if available otherwise they grow without oxygen.

1. Obligate anaerobes; oxygen is essential for their growth (mycobacterium tuberculosis)
2. Obligate anaerobes; they cannot grow in the presence of oxygen (Clostridium tetani)
3. Facultative anaerobes; they can use oxygen if present. otherwise they grow without oxygen (Escherichia coli)


Genetic aspects of bacteria

Bacteria contain both DNA and RNA as their genetic material. But the compositions of these genetic materials are different from that of eukaryotic genetic material. They have a single circular DNA and the molecular weight is about 2 × 109 and composed of 5×106 base pairs. Bacteria are haploid whereas eukaryotic cells are diploid. Haploid means that they have a single copy of genetic material.