ABSTRACT
Mycoplasmas are minute prokaryotic organisms, highly pleomorphic, varying in shape from spherical structures with diameters of about 125 to 250 nm to slender branched filaments of uniform diameter, and ranging in length from a few μm to 150 μm. Their mode of reproduction is still controversial. According to Freundt,1 the cells, during growth, go through a cycle of morphological changes, commencing with a small spherical particle or elementary body, from which one or more short, thin filaments emerge. The filaments lengthen and branch frequently, so that in the first 12 to 18 hours of growth a mycelial structure develops (hence the name Mycoplasma, fungus form). Regularly spaced spheres of uniform size and shape then form within the filaments. Subsequently constrictions develop between the spheres, dividing the filament into a chain of coccoid elements. By disintegration of the chain the spherical elements are liberated and are considered to be new elementary bodies. On the other hand, several authors, in particular Furness,2 claim that mycoplasmas reproduce by simple binary fission. However, there is no essential difference between the two schools of thought. Recent studies have shown that the replication of the mycoplasma genome is semiconservative, like that of the typical prokaryotic genome of the eubacteria.3 The various mycoplasmas may differ in the stage at which division of the cytoplasm takes place. It may either be synchronized with the replication of the genome, resulting in characteristic binary fission, or it may be delayed, leading to the formation of multinucleate filaments. The degree of synchronization of genome replication and cytoplasmic division may be a characteristic of the Mycoplasma species, though it also varies within the same species with the age of the culture and the growth conditions. Morphology and mode of reproduction can, therefore, not be taken as definite criteria for distinguishing between different mycoplasmas.
