Actinomyces hordeovulneris, a canine pathogen that produces L-phase variants spontaneously with coincident calcium...

The spontaneous production of cell-wall-deficient filaments and protoplasts by a strain of Actinomyces hordeovulneris (UCD 81-332-9) in 10% sucrose L-form media is reported. Multiple mineral deposits were present within the variants at 48 hours. Electron microscopy revealed that these deposits were amorphous, dense, and at the inner face of the cytoplasmic membrane in wall-less protoplasts and also in filaments which had a thin wall of 10 nm. These cell-wall-deficient variants produced L-form colonies when cultured for an additional 48 hours on 10% sucrose-BYE L-form plates. The colonies were composed of only a few filaments and many vesicles which were negative with Dienes' stain. Silver substitution stains of UCD 81-332-9 cells that had been grown in L-form broth for 5 days revealed heavy calcification of all cells including protoplasts. Gram stains of L-form grown cells revealed the presence of long-beaded, infrequently branched gram-positive filaments similar to those observed in clinical specimens. The formation of cell wall-deficient variants with coincident mineralization is believed to be related to the phenomenon of sulfur granule formation in vivo.