Reproduction

The normal method of reproduction in bacteria is by asexual methods. Genetic recombination also takes place in some cases, and these methods have been included under sexual reproduction.

I. Asexual reproduction.

Bacteria reproduce by asexual methods like transverse binary fission, filament fragmentation and budding.

1. Transverse binary fission is the most common type of reproduction in bacteria. The bacterial cell divides into two daughter cells of equal sizes. Cell division is of a simple type called amitosis, in which no spindle formation takes place.

2. Filament fragmentation. Some bacteria, e.g., Actinomycetale, reproduce by giving off a filament which breaks up into units, each of which forms a cell.

3. Budding. Some bacteria reproduce by budding. The parent cell gives off a small outgrowth (bud) which then pinches off as a new cell. This cell is much smaller than the parent cell.

II. Sexual Reproduction

Under this heading have been included processes in which genetic recombination occurs. Three methods of genetic recombination are known, conjucgation, transformation and transduction.

1. Conjugation. In conjugation there is a transfer of genetic material between two conjugants belonging to sexually different strains.
The first step is conjugation is the mutual recongnition of ‘male’ and ‘female’ cells. This is achieved by complementary surface molecules, the male component of which is formed by the F factor or sex factor.
Bridge formation A conjugation bridge is formed between the two conjugants. This bridge is formed between the two conjugants. This bridge is formed by the two or three special hollow F-pili of the male.
DNA transfer takes place slowly from the male cell to the female cell through the groove in the F-pilus. This transfer is energy-dependent. The male cell transfers a part of its chromosome, or the entire chromosome, to the female cell

2. Transformation. In transformation the living cell picks up fragments of DNA that have been released by dead cells. Thus, the living cell gets additional DNA. They found that addition of DNA from capsule-producing cells to a culture of non-capsulated cells transformed the latter, and enabled them to produce capsules.

3. Transduction. In transduction, fragments of DNA are carried from one bacterial cell to another by bacterial viruses. Transduction is of two types, generalized and specialized. In generalized transduction the bacteriophages may transfer any bacterial genes.