Question

Please answer both questions, Thank you!

1. What are the basic ways microorganisms exchange DNA?
2. Discuss how bacteria protect themselves from invading bacteriophages.

Answer 1

1--There are three basic pathways through which microorganisms can exchange DNA. They are as follows :

a) Conjugation : When the transfer of DNA occurs through direct cell-cell contact, then it is called Conjugation. Generally, this DNA transfer happens through a tubular structure called sex pilus. The donor cell will produce pilus and it will get attached to recipient cell, hence bringing them together. Now DNA in form of conjugative plasmid will travel through this tubular pilus from the donor cell to the recipient. This is how Conjugation mechanism is explained in simpler terms.

b) Transformation : When the bacteria takes up the fragments of floating DNA from the surrounding environment through its cell membrane and then integrates it in its genome, then it is called Transformation. This stray DNA might come from lysed or dead bacterial cells and other pathogens.

c) Transduction : When the transfer of DNA is mediated by some bacteria-infecting viruses (called bacteriophages), then it is called Transduction. It is a much more efficient method of horizontal gene transfer among bacteria. What basically happens here is that fragments of host DNA are trapped into bacteriophage. When these bacteriophage infects the healthy bacteria, then this DNA is also transferred to it. Now this DNA will be replicated and then expressed in the infected host through its own cell machinery. And this cycle will keep on continuing, depending upon the life-cycle of virus (Lytic or Lysogenic)

2-- There are two underlying mechanisms through which bacteria protect themselves from invading bacteriophages:

a) Through Restriction Endonucleases : Restriction Endonucleases are the special enzymes which have the capability to cleave or fragment the DNA sequence at specific sites. So whenever the bacteriophage inserts its DNA, then these enzymes cleave this invading DNA into small fragments which are further decraded by cell.

b) CRISPR-Cas : It stands for Clustered Regularly Interspaced Short Palindromic Repeats - . What basically happens here is that the bacteria will keep a snapshot or memory of the invader bacteriophage by retaining its genetic material. These fragments are then copied into CRISPR arrays, which ultimately help the bacteria to remember the invader. When the bacteriophage invades again, then it is compared with it. Once the match is found, then the Cas protein will fragment and chop the Viruses' DNA again, hence protecting it again. The fragments are retained by the cell again to improve the recognition further.

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