Q.3 The bacteria known to be naturally competent for transformation of DNA is

• (A) Escherichia coli
• (B) Bacillus subtilis
• (C) Mycobacterium tuberculosis
• (D) Yersinia pestis

  Bacterial competence enables natural DNA uptake, a key horizontal gene transfer mechanism in microbiology and genetics. For biotech students prepping exams, knowing naturally competent species is crucial. This article solves the MCQ with the correct answer—(B) Bacillus subtilis—and details all options.

  What is Natural Competence?

  Natural competence allows bacteria to take up exogenous DNA without artificial treatments like heat shock or electroporation. It involves competence pili (pseudopili) for DNA binding, transport via ComEC/ComFA proteins, and RecA-mediated recombination. Gram-positive Bacillus subtilis exemplifies this under nutrient stress via quorum sensing (ComK regulon).

  Correct Answer: (B) Bacillus subtilis
  B. subtilis develops natural competence in stationary phase, expressing ~40 genes for DNA uptake. Strains like 168 transform efficiently with linear DNA, making it a model for genetic studies and protein expression .

  Explanation of All Options

  Evaluate each bacterium’s transformation ability:

  • (A) Escherichia coli
    Incorrect. E. coli (K-12, B strains) lacks natural competence; lab strains require chemical (CaCl₂) or electroporation for plasmids. No native Com machinery exists.

  • (B) Bacillus subtilis
    Correct. Naturally competent under competence-inducing conditions (e.g., glucose starvation). DNA binds ComGA/ComEA, translocates via ComEC, integrates via homologous recombination.

  • (C) Mycobacterium tuberculosis
    Incorrect. Mtb shows low/no natural competence due to thick mycolic acid cell wall. Genetic manipulation uses phage delivery or electroporation, not spontaneous uptake.

  • (D) Yersinia pestis
    Incorrect. Plague bacterium Y. pestis has no reported natural competence. Pathogenic Yersinia relies on conjugation/transduction; transformation is artificial.

  Option	Natural Competence?	Key Reason	Example Use
  (A) E. coli	No	Requires lab induction	Cloning via CaCl₂
  (B) B. subtilis	Yes	Quorum-sensing ComK	Genetic mapping
  (C) M. tuberculosis	No	Thick cell wall	Phage transduction
  (D) Y. pestis	No	Pathogen adaptations	Artificial methods

  Biotech Relevance

  B. subtilis’s competence aids cloning, genome editing (e.g., CRISPR integration), and industrial enzyme production. Unlike artificial systems, it supports ecological HGT studies. Pair with bioinformatics tools like BLAST for sequence confirmation in molecular biology workflows [user-information].