SEXUAL REPORDUCTION IN BACTERIA

In bacteria sexual reproduction is of three types :

Transformation : The process of uptake of a complete or fragment of a naked DNA molecule by a competent cell from the medium and incorporation of this molecule into recipient chromosome in a heritable form is called as transformation. This type of gene transfer is discovered and demonstrated by Fred Griffith. The process of transformation is random and any portion of a genome may be transferred between bacteria. The process of transformation is an important and natural route of genetic exchange in bacteria. The transformation, as natural phenomenon, is found only in certain gram +ve and gram –ve bacteria such as Streptococcus, Bacillus, Thermoactinomyces Haemophilus, Azotobacter, Pseudomonas etc. In laboratories, the transformation is carried out artificially by treating the cells with calcium chloride. This treatment makes the cell membrane more permeable to DNA. However, the frequency of the transformation increases with high concentration of DNA.

Conjugation : The process of transfer of genetic material from one cell to another cell through direct cell-cell contact is called as conjugation. This process of conjugation was discovered in E.coli by J.Lederberg and E.L. Tatum in 1976. Later, scientists namely Hayes, Jacols and wollman proved that gene transfer in this process occurs only in one direction and it is non- reciprocal. This one-way gene transfer takes place from male or donor cell to female or recipient cell. Normally much longer DNA fragment is transferred in this conjugation process when compared to that of transformation process. Besides the main chromosome, some of the bacterial cells contain one or more. Small DNA molecules called as plasmids. This extra chromosomal genetic material can also be transferred from one cell to another cell through conjugation process.

Transduction : Transduction is defined as a process of genetic transfer from donor bacterial cell to recipient bacterial cell mediated through a bacteriophage. This process is first discovered by Norton Zinder and Joshua Lederberg in Salmonella, by a variety of bacteriophages. Transduction is one of the most common mechanism for gene exchange and recombination in bacteria. There are two type of transduction processes namely generalized transduction and specialized transduction.