Cell Inclusions and the Life Cycle of Azotobacter

Abstract

The complicated life cycle described by Lohnis and Smith (1916, 1923) for Azotobacter has not been fully confirmed by subsequent investigation. Jones (1920) who had previously reported reproduction by gonidia, accepted the doctrine of symplasm but was not able to confirm conjunction, the formation of endospores, or filtrability. Mulvania (1919) confirmed reproduction by budding and gonidia. de Regel (1932) accepted the gonidial method of reproduction and filtrability but rejected conjunction, symplasm, and transmutation of cells. Beauverie (1925) failed to confirm any of the salient features of a cyclogenic life history. In view of the conflicting results obtained by various workers

A Cytological Study of a Pleomorphic Strain of Azotobacter With the Electron and Phase Microscopes and the Robinow Nuclear-Staining Technique

“…Granules in the cells of Azotobacter have been variously described as fat bodies, volutin, gonidia, and chromidia. Although some investigators have contended that these granules were reproductive organs (Jones, 1913;Mendl, 1911), others have disputed this contention (Bonazzi, 1915;Lewis, 1937Lewis, , 1941. The present investigation indicates that these granules probably do represent the nuclear bodies that have been described for some of the other bacteria, since bodies in young cells are easily stained when prepared according to procedures for distinguishing desoxyribonucleic acid; older cells lose this property.…”

“…In addition to large rods, small rods, elongated and branched cells, and minute coccoid cells, these authors described dwarfed cells, small sporulating rods, and large sporulating rods. Other investigations have not confirmed the presence of heat-resistant endospores in this organism (Jones, 1920;Lewis, 1937).…”

The Azotobacteriaceae

“…L6hnis and Smith (13) have gone farthest in this respect and described a complex "life cycle" comprising many different types of organisms as stabilized stages. This has not been confirmed by later investigators (14,15,16,17,18,19,20,21), who have mostly explained L6hnis and Smith's results as due to latent contaminants that often are difficult to eliminate from the cultures of Azotobacter; this explanation, indeed, would hardly account for the reported regeneration of normal azotobacter from some of the aberrant forms, e.g., the so-called "fungoid form" studied by Lbhnis and Smith. Yet the morphology of Azotobacter in reliably pure cultures is remarkably variable, and general agreement seems to exist that the following cell types occur:…”

Encystment and germination in Azotobacter vinelandii.

“…The morphogenetic process yields a resting cell, the central body, which is encased in an inner coat, the intine, and an outer coat, the exine (175). The lipid accumulations in the central body consist of PHB (48, 95,96,152) Cysts are oblate spheroids whose axes are 1.5 ,um and 2.0 ,m, respectively, and thus they are approximately half the volume of vegetative cells. They germinate at 30 C in aerated Burk's N-free buffer with a variety of compounds as germination agents, which must also serve as growth substrates (101).…”