The fine structure of Herpetosiphon, and a note on the taxonomy of the genus.

The fine structure of the Gram-negative filamentous gliding bacterium, Herpetosiphon is described. The outer membrane of the cell envelope could not be resolved as a separate structure, probably because it is fused with the underlying dense (peptidoglycan) layer. There was an additional wall layer outside this membrane-peptidoglycan complex, but a sheath in the classical sense, as postulated in the definition of the genus, was lacking. On the cell surface a loose network of fibrils could be seen. Inside the cells 3 types of intracytoplasmic membranes were discernible: a) true mesosomes near cross walls; b) a system of coarser membranes which was not connected with the septa and formed networks or tubular complexes; c) degenerated septa within bulbs. The bulbs are swollen sections of filaments, occurred mainly in ageing cultures, and are probably a degeneration phenomenon. The filaments contained necridia, i.e. dead and empty cells, across which breaks may occur so that empty cell wall cylinders remain attached to the ends of the daughter filaments, falsely suggesting the presence of a sheath. The taxonomy of Herpetosiphon is discussed in detail: The organism has been described before as Flexibacter giganteus. It is proposed to abandon the species H. aurantiacus in favor of H. giganteus, but to retain the genus Herpetosiphon. An improved definition of the genus is given.