Question:
Which bacterium possesses two circular chromosomes?
Which bacterium possesses two circular chromosomes?
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The comma-shaped cholera bacterium famously has a divided (two-chromosome) genome.
Updated On: Jun 25, 2026
- Escherichia coli
- Vibrio cholerae
- Mycobacterium tuberculosis
- Mycoplasma genitalium
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The Correct Option is B
Solution and Explanation
Step 1: Recall the usual bacterial genome.
Most bacteria carry a single circular chromosome. E. coli, M. tuberculosis and Mycoplasma genitalium all follow this pattern (the last having one of the smallest genomes known).
Step 2: Identify the exception.
Vibrio cholerae is the classic example of a bacterium with two distinct circular chromosomes - a large chromosome 1 carrying most essential genes and a smaller chromosome 2 (originally a megaplasmid that became indispensable). This divided genome is a favourite exam point.
Step 3: Why the other options are wrong.
• E. coli - one circular chromosome (plus optional plasmids).
• M. tuberculosis - single circular chromosome, GC-rich.
• Mycoplasma genitalium - single tiny circular chromosome, no cell wall.
Key fact: Vibrio cholerae uniquely has two circular chromosomes among the options.
Most bacteria carry a single circular chromosome. E. coli, M. tuberculosis and Mycoplasma genitalium all follow this pattern (the last having one of the smallest genomes known).
Step 2: Identify the exception.
Vibrio cholerae is the classic example of a bacterium with two distinct circular chromosomes - a large chromosome 1 carrying most essential genes and a smaller chromosome 2 (originally a megaplasmid that became indispensable). This divided genome is a favourite exam point.
Step 3: Why the other options are wrong.
• E. coli - one circular chromosome (plus optional plasmids).
• M. tuberculosis - single circular chromosome, GC-rich.
• Mycoplasma genitalium - single tiny circular chromosome, no cell wall.
Key fact: Vibrio cholerae uniquely has two circular chromosomes among the options.
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