spheroplasts

A spheroplast is a cell whose cell wall has been partially removed, leaving a spherical cell bounded by the plasma membrane and, in many bacteria, an outer membrane. Spheroplasts are most commonly described for Gram-negative bacteria, but the term is also used for plant-derived cells whose walls have been enzymatically removed to form protoplasts.

In bacteria, spheroplasts arise after enzymatic digestion of peptidoglycan with enzymes such as lysozyme and agents like EDTA that disrupt the cell wall and outer membrane. The outer membrane may remain intact in Gram-negative organisms, while the peptidoglycan layer is diminished. Because the cell wall is largely removed, spheroplasts are osmotically fragile and require isotonic or hypertonic media (for example, sucrose or mannitol) to prevent lysis. They can revert to wall-bearing cells when cell wall synthesis resumes.

Spheroplasts differ from protoplasts. Protoplasts refer to cells that lack a cell wall entirely and can arise from both Gram-positive and Gram-negative organisms, whereas spheroplasts retain residual wall material or the outer membrane in many cases.

Applications of spheroplasts include studies of cell wall biogenesis, membrane transport, and macromolecule uptake. They are used in genetic transformation and recombination experiments and in bacteriophage research. In plant biology, the term can describe plant protoplasts formed by enzymatic removal of the cell wall, which are used for somatic cell fusion, genetic manipulation, and regeneration into new plant tissue.

Handling and safety: Spheroplasts require careful handling to avoid osmotic shock. They are typically manipulated in sterile conditions with osmotically stabilized buffers and rapid processing to minimize lysis.