Patterns of growth and gliding motility inSimonsiella

Abstract

Forty-six strains ofSimonsiella—large, Gram-negative, aerobic, multicellular filamentous, gliding bacteria from the oral cavities of cats, dogs, sheep, and humans—were grown under various environmental conditions to elucidate features of gliding motility in the genus. Under standard growth conditions on bovine serum-tryptic soy-yeast extract (BSTSY) agar at 37°C, few strains glided. Nongliding strains displayed edges of microscopic colonies ranging from entire to rhizoid (filamentous outgrowth). Gliding strains displayed motility on agar in individual, often well-separated filaments, forming etched tracks in the agar. In some strains, gliding on agar led to the formation of satellite colonies, suggesting that motility is a possible mechanism for sustaining growth. Gliding was often pronounced in regions of heavy growth bordering on unoccupied agar surfaces, suggesting that motility might be triggered by growth metabolite accumulations, but, also, might require certain levels of fresh nutrients. Motility rates of 4- to 12-h-old cultures of selected strains in BSTSY broth or on BSTSY plus 0.5% agar (measured in sealed slide preparations held at approximately 37°C) ranged from 5 to 23.8 μm/min. Rate variations, obtained for the same as well as different trials, would be expected due to variations in oxygen tension and in metabolite and nutrient concentrations on agar sealed under glass.