Which genus is characterized by lacking a cell wall and being among the smallest free-living bacteria?

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Multiple Choice

Which genus is characterized by lacking a cell wall and being among the smallest free-living bacteria?

The point here is that some bacteria lack a cell wall, and among the smallest free-living forms are in the genus that has no peptidoglycan in its envelope. In these organisms, the cell wall is absent, so the membrane is directly exposed. To keep the cell intact without a rigid wall, their cytoplasmic membrane contains sterols, which help stabilize and protect the cell. This makes them typically pleomorphic, and they are among the tiniest free-living bacteria, often around a few tenths of a micron in diameter. Because there is no cell wall, these organisms do not stain well with the classic Gram stain, which relies on wall structure to retain the dye. They also behave differently with antibiotics: many drugs that target cell wall synthesis are ineffective against them. In contrast, the other organisms mentioned all have cell walls—Staphylococcus and Streptococcus species with peptidoglycan-rich walls, and Mycobacterium tuberculosis with a waxy, mycolic-acid–rich outer layer—so they do not fit the description.

The point here is that some bacteria lack a cell wall, and among the smallest free-living forms are in the genus that has no peptidoglycan in its envelope. In these organisms, the cell wall is absent, so the membrane is directly exposed. To keep the cell intact without a rigid wall, their cytoplasmic membrane contains sterols, which help stabilize and protect the cell. This makes them typically pleomorphic, and they are among the tiniest free-living bacteria, often around a few tenths of a micron in diameter.

Because there is no cell wall, these organisms do not stain well with the classic Gram stain, which relies on wall structure to retain the dye. They also behave differently with antibiotics: many drugs that target cell wall synthesis are ineffective against them. In contrast, the other organisms mentioned all have cell walls—Staphylococcus and Streptococcus species with peptidoglycan-rich walls, and Mycobacterium tuberculosis with a waxy, mycolic-acid–rich outer layer—so they do not fit the description.

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