Structural and physiological characteristics of some sheathed bacteria.

The fine structure and growth of two gram-negative and two gram-positive strains of sheathed bacteria, isolated from activated sludge, have been studied. Their anatomy is quite different from Sphaerotilus natans. The cells are rectangular, tightly joined together, non-motile and enclosed by a sheath which is thin in the gram-negative strains and rather electron-dense in the two larger gram positive strains. The four strains grow slowly and form pink filamentous flocs in liquid media.