Protoplasts and spheroplasts are altered forms of bacteria or yeast, in which the principal shape-maintaining structure of the bacteria is weakened. Each bacterium forms a sphere, which is the shape that allows the bacterium to withstand the rigors, particularly osmotic, of the fluid in which it resides.

The term protoplast refers to the spherical shape assumed by Gram-positive bacteria. Spheroplast refers to the spherical shape assumed by Gram-negative bacteria. The difference is essentially the presence of a single membrane, in the case of the protoplast, and the two membranes (inner and outer) of the Gram-negative spheroplasts. It is also possible to generate a gram-negative protoplast by the removal of the outer membrane. Thus, in essence, protoplast refers to a bacterial sphere that is bounded by a single membrane and spheroplast refers to a sphere that is bounded by two membranes.

Bacteria are induced to...