Electron micrographs made from L forms of Proteus and two human strains of pleuropneumonia-like organisms.

The organisms in the cultures of the pleuropneumonia group and of the L forms of bacteria are visible with the light microscope. Their morphology has remained controversial for a long time because they are easily deformed in microscopic preparations and give riise to bizarre forms. It seems well established at present (Klieneberger and Smiles, 1942; Dienes, 1945) that the cultures, with a few exceptions, consist of round forms which vary in size by continuous transition from barely visible ones to those several micra in diameter. The exceptions are the organisms of bovine pleuropneumonia and of agalactia in the cultures of which the small granules grow out into fine branching filaments which later develop swellings or break up into other granules. According to Freundt (1952), branching filaments also are present occasionally in the cultures of other pleuropneumonia-like strains. Reproduction occurs either by binary fission as in bacteria or by the production of small forms in varying numbers inside the larger ones (Dienes and Weinberger, 1951). The size of the smallest viable element in one bacterial L form, an old Li isolated from Streptobacillus moniliformis (Klieneberger-Nobel, 1949), has been determined by filtration through gradocol membranes. It was found to be at the borderline of visibility between 0.175 and 0.25 I,u about the same as in the pleuropneumonia group. The electron micrographs of these organisms which have been published have added little new information on their morphology (Freundt, 1952; Smith et al. 1948a, b). The fragility of the organisms made it difficult to make preparations appropriate for electron micrography. We had 1 This is publication no. 145 of the Robert W. Lovett Memorial Foundation for the Study of Crippling Diseases, Harvard Medical School. 2 The expenses in connection with this investigation were defrayed by grants from the Commonwealth Fund and the United States Public Health Service. similar difficulties with agar cultures of L forms of Salmonella and Proteus species and obtained appropriate preparations only from the floating cultures of the Proteus L described in the preceding paper (Dienes, 1953). On the other hand, repiesentative micrographs were obtained without difficulty from the cultures of an oral and of a genital strain of human pleuropneumonia-like organisms (Dienes and Madoff, 1953). A selection of these micrographs is presented in this paper. To facilitate the interpretation of the electron micrographs, photographs obtained with light microscopy from stained preparations an(d with phase contrast from the same cultures also are presented.3