gliding bacterium, any member of a heterogeneous group of microorganisms that exhibit creeping or gliding forms of movement on solid substrata. Gliding bacteria are generally gram-negative and do not possess flagella. The complex mechanisms by which they move have not been fully ascertained, and such mechanisms differ among various species. The gliding bacteria include the fruiting myxobacteria (e.g., Myxococcus and Cystobacter); the cytophaga group of nonfruiting, nonphotosynthetic rods or chains (e.g., Cytophaga and Sporocytophaga); and certain filamentous bacteria such as Thiothrix, Simonsiella, and Leucothrix. Gliding bacteria are found in soils and in fresh and marine waters. Simonsiella inhabits the oral cavities of humans and animals. The filaments of Beggiatoa resemble filamentous cyanobacteria; they are found in sulfur-rich deposits and hydrothermal vents.