A cytological study of a pleomorphic strain of Azotobacter with the electron and phase microscopes and the Robinow nuclear staining technique.

L6hnis and Smith (1923) pointed out that not less than seven different morphological types can be developed and stabilized from Azotobacter cultures. This extreme transmutation of cells has been questioned by subsequent investigators (Lewis, 1937, 1941). Nevertheless, peculiar morphological phases do occur in Azotobacter cultures and no satisfactory explanation has been given as to their function. Several new techniques, as well as some new concepts, have been developed since these earlier workers debated the significance of the morphological cell types in Azotobacter species. The purpose of the investigation now being reported was to see whether phase microscopy, electron microscopy, and nuclear staining might add information concerning the cytology of Azotobacter. Also, recent discussions of sexuality and peculiar reproductive processes in bacteria (Dienes, 1946; Lederberg, 1948) encouraged the authors of this paper to search for nuclear arrangements among large bacteria, such as in the genus Azotobacter.