Question

Differentiate genome reduction from horizontal gene transfer. Specifically in bacteria.

Answer 1

Genome reduction or Genome degradation is the process by which the genome size of an organism gets reduced when compared with their ancesters. This is most significant in case of bacteria and it is also a major contributor of evolution. The process of genome reduction is more visible in obligate endosymbionts. These organisms are a complete dependent of their host and without their host they cannot survive. So, as they are present within the host, and completely dependent on them, they undergoes a reduction in their genome. They deletes all the genes in course of time which are not required for them and keeps only the essential genes. Typical example includes the genome reduction in Buchnera aphidicola which is an endosymbiont of aphid.

On the other hand, Horizontal gene transfer (HGT) also called as Lateral Gene Transfer is the movement of genetic material from one organism to another. The process of HGT is more obvious in bacteria which occurs by 3 different mechanisms. They include either Conjugation, Transformation or Transduction.

Conjugation is the process in which the genetic material is transferred from an F+ donor bacterium to an F- recipient bacterium through a sex pilus. It requires close contact between an F+ strain and an F- strain.

Transformation involves the uptake of short fragments of DNA by naturally transformable bacteria from the sorrounding medium while transduction is the process where gentetic material is transferred between one bacteria to another via a bacteriophage (viruses that infect bacteria).

An important example for horizontal gene tranfer includes the spread of Antibiotic resistance among bacteria.

Like Genome reduction, Horizontal gene transfer is also a major contributor of evolution.