Which of the following bacteria possesses two circular DNA molecules (i.e., two distinct chromosomes) in its genome?

Appeared in: INI-CET EXAM -2026

Explanation

Vibrio cholerae is unique among the given options as its genome is divided into two separate circular chromosomes.
Chromosome 1, the larger of the two, carries the primary virulence factors, including the genes for cholera toxin, which are essential for causing the disease cholera.
Chromosome 2 is smaller and carries genes important for adaptation, environmental survival, and antibiotic resistance, contributing to the bacterium's overall fitness.

Option A: Escherichia coli, a common cause of urinary tract infections and gastroenteritis, possesses a single large circular chromosome. It is a model organism for studying bacterial genetics based on this single-chromosome structure.
Option C: Salmonella typhi, the causative agent of typhoid fever, has a genome consisting of one circular chromosome, similar to other members of the Enterobacteriaceae family.
Option D: Shigella dysenteriae, which causes bacillary dysentery, is genetically very similar to E. coli and also has a single circular chromosome.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Bacterial genetics and genomic structure as background academic context rather than a clinical decision trigger.
Understanding the unique two-chromosome structure of V. cholerae is vital for research into its pathogenesis, evolution, and the development of novel antimicrobial strategies targeting its specific genetic organization.
The segregation of essential and virulence genes on Chromosome 1 makes it a primary target for vaccines and treatments against cholera.
The presence of adaptive genes on Chromosome 2 explains the bacterium's resilience and ability to acquire resistance, which is a key consideration in managing cholera outbreaks and treatment failures.

How to Approach the Question

This is a factual recall question from microbiology. The goal is to identify the bacterium with a specific, unusual genomic feature.
First, carefully read the question to identify the key characteristic being asked: 'two circular DNA molecules' or 'two distinct chromosomes'.
Next, review the options provided: Escherichia coli, Vibrio cholerae, Salmonella typhi, and Shigella dysenteriae.
Access your knowledge base on bacterial genetics. Recall that the vast majority of bacteria have a single circular chromosome. The distractors (E. coli, Salmonella, Shigella) are all classic examples of this common structure.
Identify Vibrio cholerae as the well-known exception among the choices, famous in microbiology for its bipartite genome (two chromosomes).
Confirm that this unique feature matches the question's requirement and select Vibrio cholerae as the correct answer.

Concept Tested & Keywords

Concept Tested: Bacterial genetics and genomic structure
Stem keywords: bacteria, two circular DNA molecules, two distinct chromosomes, genome
Lead-in keywords: Which

QbYffi2RkGZQ7ABPYiolrZ

Practise the full INI-CET EXAM -2026

Attempt every question from this paper in a timed mock, then review the full solution for each one.