A hypothesis for the mechanism of mycoplasma evolution

Mycoplasmas are wall-less prokaryotes which have small genomes and are known to have evolved from ancestors of Gram-positive bacteria. A model is proposed to explain how mycoplasmas may have evolved from these ancestors which had cell walls and large genomes. It is proposed that the initial step in this process was loss of the cell wall and conversion of the ancestral bacterium to an L-form. Fusion of L-forms would have resulted in a single cell that contained two or more complete genomes. It is thought that this bringing together of multiple genomes by cell fusion resulted in genetic recombination between genomes and loss of DNA segments from the cell. Data from bacterial systems are cited in support of this model.