Morphology and Reproductive Processes of the L Forms of Bacteria II. Comparative Study of L Forms and Mycoplasma with the Electron Microscope

Representative electron micrographs, from the study of eight strains of L forms and one strain ofMycoplasma , are presented. A- and B-type L forms were derived from two strains ofProteus , two other L forms were derived from a diphtheroid and from a staphylococcus strain, and two strains (designated as LX) were isolated from L forms derived from a group A β-hemolytic streptococcus and from a staphylococcus. TheMycoplasma strain was isolated from goats. Sections were made of young colonies grown within agar and from parts of surface colonies embedded in the agar. B-type L colonies ofProteus were produced by inoculation of bacteria into media containing penicillin. The large bodies developing from the bacteria and the organisms in B-type L colonies ofProteus , like the parent bacteria, had a cell wall consisting of a plasma membrane and an outer cell wall. The loss of rigidity in the cell wall indicated an alteration in its structure. The A-type L cultures ofProteus consisted of irregular branching masses extending in several directions, of small dense organisms corresponding to the elementary corpuscles present in cultures ofMycoplasma , and of intermediary forms. In contrast to the B-type, all organisms in the A-type colonies were surrounded by a single unit membrane corresponding to the plasma membrane of bacteria. The structures inside the cell membrane, both in the A- and B-type, seemed to correspond to the structure of the parent bacteria, which contained ribosomes and threads of DNA. The elementary corpuscles formed chains and filaments, and, apparently, these corpuscles took part in the multiplication by gradual enlargement. The organisms seen in the cultures of all L forms andMycoplasma studied, except in the B-type L forms ofProteus , corresponded in size, shape, and structure, as well as in the development of elementary corpuscles, to the organisms in the A-type L form ofProteus . In contrast to the spherical organisms usually seen in broth cultures, the organisms in young cultures ofMycoplasma , which were grown within the agar, were similar in morphology, as well as in the discernible structure of the organisms, to L forms. Significant morphological and structural differences were not apparent between the L forms andMycoplasma (in cultures grown within agar media) under the conditions of this investigation.