Smallest genome among listed bacteria Among the organisms listed, which one has the smallest genome size?

Introduction / Context:
Genome size correlates with metabolic independence and lifestyle. Minimal genomes are often found in parasitic or symbiotic bacteria with reduced biosynthetic capabilities. Recognizing organisms with very small genomes helps connect evolutionary reduction with culture difficulty and host dependence.

Given Data / Assumptions:

• Compare approximate genome sizes among named bacteria.
• Well-known reference sizes: M. genitalium (~0.58 Mb), H. influenzae (~1.83 Mb), M. tuberculosis (~4.4 Mb), E. coli K-12 (~4.6–4.7 Mb).
• Select the smallest among options provided.

Concept / Approach:

Mycoplasma genitalium is famous for having one of the smallest genomes of any free-living bacterium, long used in minimal genome studies. Therefore, it is smaller than H. influenzae and much smaller than M. tuberculosis or E. coli.

Step-by-Step Solution:

Verification / Alternative check:

Historic milestones: H. influenzae was the first free-living organism sequenced, but M. genitalium retains the notoriety for a much smaller genome, guiding minimal gene set projects.

Why Other Options Are Wrong:

• H. influenzae: Larger than M. genitalium.
• M. tuberculosis and E. coli: Substantially larger genomes.
• None of these: Incorrect because M. genitalium is listed and is the smallest.

Common Pitfalls:

• Confusing “first sequenced” (H. influenzae) with “smallest genome.”

Final Answer:

Mycoplasma genitalium