Solved Gate Questions

The bacteria known to be naturally competent for transformation of DNA is ? (GATE BT 2010)

The bacteria known to be naturally competent for transformation of DNA is ? (GATE BT 2010)

a) Escherichia coli b) Bacillus subtilis
c) Mycobacterium tuberculosis d) Yersinia pestis

Correct answer is (B) Bacillus subtilis

Note: Details below are mostly verbatum of the reference mentioned in the end:

About Natural Competence for Transformation:

Natural competence refers to the ability of some bacteria to actively transport environmental DNA fragments across their cell envelope and into their cytoplasm. This characteristic provides the competent bacteria with a very useful Horizontal Gene Transfer (details on gene flow/transfer:CLICK HERE ) mechanism. Not only this, the extra-cellular DNA acts as a source of nutrients as well.

How Natural Transformation occurs? :

Naturally competent Gram-negative bacteria are known to take up extra-cellular DNA in two stages:

competence

1) DNA Uptake: Across the outer membrane

and

2) DNA translocation: Across the inner membrane

Step A in Fig. 1 depicts the extra-cellular DNA bound to the cell

Step B in Fig 1 depicts the uptake of DNA through retraction of T4P fibres (cell surface fibers of the type IV pilus family), which pulls the DNA into the periplasm through secretin pores in the outer membrane.

T4P fibres are known to form long pili (which are used for adhesion/twitching motility) in some species.

Gram-positive bacteria also use similar T4P related proteins to pull double-stranded DNA across their thick cell walls.

Figure 2 represents the possible fates of the DNA taken into the cell.

competence2

For discussions and details on Transformation and other gene transfer techniques,: CLICK HERE.

Images and literature referred from:

Mell, J.C., and Redfield, R.J. (2014). Natural competence and the evolution of DNA uptake specificity. J. Bacteriol. JB.01293–13.
 

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