Cytophysiological Characteristics of the Vegetative and Dormant Cells of Stenotrophomonas sp. Strain FM3, a Bacterium Isolated from the Skin of a Xenopus laevis Frog

A bacterial strain (FM3) that is closely related to Stenotrophomonas acidaminiphila and S. maltophilia, was isolated from the skin surface of the frog Xenopus laevis. Cytophysiological studies on vegetative cells and cyst-like cells (CLCs) that were obtained in model experiments addressed the dynamics of transition of vegetative cells to the dormant state and their reversion to vegetative growth. The ultrastructural organization of the vegetative and dormant cells of strain FM3 possesses unique properties. Cultures that developed after inoculating vegetative cells were characterized by: (1) resistance to physical factors and sterilization procedures; (2) high antimicrobial activity with respect to some gram-positive and gram-negative bacteria; (3) resistance to polypeptide antibiotics; (4) the presence of an easily detaching S-layer on the cell surface; (5) the ability to secret outer membrane vesicles into the intercellular space; and (6) formation of S-layerderived tubular structures associated with outer membrane vesicles that are regularly arranged within the tubes. Dormant cells were characterized by: (1) resistance to dehydration; (2) resistance to high temperatures; and (3) the preservation of the S-layer on the surface of cystlike cells (CLCs). Depending on experimental conditions, strain FM3 formed three CLC morphotypes, which differed in their abundance and ultrastructural organization. The experimental conditions used for CLC formation approximated those under which bacteria survive in hospitals. A model of intermicrobial parasitism is suggested that applies to motile FM3 cells during the development of their populations (cultures).