Ultrastructure of square bacteria from a brine pool in Southern Sinai.

The square bacterium discovered by Walsby (Nature [London] 283:69-71, 1980) has been shown to possess the ultrastructural features of a typical halophile. The cell wall is comprised of regularly arranged subunits demonstrated by thin sectioning, shadowed replicas, and negative staining. Optical diffraction confirms the existence of both hexagonal and tetragonal arrangements of the cell wall subunits and also of different lattice constants and suggests a mixed population of bacteria.