Question

1. What are the three mechanisms of horizontal gene transfer? Describe each of the three in detail. Then go on to describe the implications of horizontal gene transfer to microbial evolution and 2. human health.

Answer 1

The three mechanisms of horizontal gene transfer include Tranformation, transduction and conjugation.

Transformation : It is the mechanism of horizontal gene transfer in which short DNA fragments of one bacteria are taken up naturally by another bacteria. Sometimes, DNA is released by one bacterium (after cell lysis) and this extracellular DNA is taken up by another bacterium. Inside the second bacteria, this extracellular DNA is broken down and exchanged with a part of the receipent bacterial DNA. This type of transfer mostly occurs in closely related species or same species of bacteria.

Transduction : This mechanism of horizontal gene transfer involves transfer of DNA from one bacterium to another which is mediated by bacteriophages. When a bacteriophage infects a bacteria, it forces it to produce phage DNA. Sometimes along with the phage DNA, bacterial DNA covered with capsid of phage is also released after lysis of the cell. When the same phage infects another bacterium, it releases this DNA into the new bacterium.

Conjugation: In conjugation, DNA is exchanged between two bacteria by pilus found on surface of bacteria. It requires close contact between the two bacteria. This transfer occurs between a conjugative plasmid and a non-conjugative plasmid, The conjugative plasmid contains all the genes necessary for the transfer and upon close contact with the non-conjugative plasmid transfers the DNA via pilus.

Horizontal gene transfers allow exchange of genetic material between microbes(bacteria and archea) by tranaformation, transduction and conjugation. This exchange of genetic material results in acquisiton of new genetic elements by a bacteria which can be a base for evolution based on how stable it is in the new bacteria and the time that will take for the incorporation in the genome for vertical transfer.  

In horizontal gene transfer, plasmids are exchanged that confers antibiotic resistant property to a bacteria. So risks of new antibiotic resistant bacteria that are harmful to humans or have the potential to be harmful increases. Also, the already existing microbes in or around the human body, if they acquire new genetic material that can change certain properties of the bacteria and so a helpful bacteria can also become harmful.