There are suggestions that homologous recombination could also be a reason for genetic exchange within and between bacterial species. However, the process of homologous recombination is more successful in integrating DNA into the chromosome when the donor and recipient are relatively closely related, and this type of genetic exchange could principally affect the variation in existing genes rather than introducing new and unique traits to the genome. Hence, its role in ecological and physiological diversification of bacteria will be insignificant. When individual genes in different organisms are compared, many instances of HGT have been observed based on the comparison of characteristics of sequences. For example, …show more content…
Natural transformations in which the uptake, integration and expression of extracellular DNA occurs under natural populations of bacteria. Through this mechanism bacteria can acquire DNA from foreign species which are not accessible to mobile genetic elements or bacteriophages. The requirement for this process is that, the bacteria should first develop a physiological state of competence. Some bacterial species, such as Neisseria gonorrhoeae and Haemophilus influenzae, are competent to accept DNA, whereas some others, such as Bacillus subtilis and Streptococcus pneumoniae, become competent after reaching a certain physiological stage in their life cycle (22,15). 2. Conjugative transfer which involves the acquisition of plasmid, and is mediated by cell to cell junctions and a pore through which DNA passes. This system has plasmid as the important component. The transfer of DNA in small units through the plasmid carriers is possible and is found to be preferred because, the transfer of whole chromosomes could take an hour, a duration too long to keep the interbacterial junction intact. Conjugation can mediate the transfer of genetic material between domains (for example, between bacteria and plants, and between bacteria and yeast; 29