Formation of multiple central bodies in giant cysts of Azotobacter vinelandii.

Cysts of Azotobacter vinelandii produced in chemical salts-agar supplemented with 0.1 to 1.0% yeast extract and 0.3% butanol (L. E. Jackson, M.S. Thesis, Univ. of Texas, Austin, 1961) were two to four times larger than cysts formed on nitrogen-free medium (Fig. 1 and 2). Microscopic studies of "giant" cysts transferred to nitrogenfree agar revealed that, prior to germination, the central body divided into two or more ellipsoidal cells (Fig. 3-6). After liberation from the exine, these cells became rods of typical azotobacter dimensions (4 to 6 ,u long). M. D. Socolofsky and 0. Wyss (J. Bacteriol. 81:946, 1961) noted that the central body usually undergoes division after germination. We have never observed multiple division of the central body in "normal" cysts, although this process occurs with great frequency in "giant" cysts. Pchon, Tchan, and Wang (Ann. Inst. Pasteur 74:182, 1948) observed that a few cells of A. vinelandii grown on glucose were transformed into large cyst-like bodies. They found these large bodies incapable of germination, clear in content, and not readily stainable. In contrast, we were able to demonstrate that the "giant" cysts were viable. "Normal" and "giant" cysts were suspended in chemical salts broth. Known numbers of cysts were spread on chemical salts-butanol-agar and incubated at 30 C. At given intervals, the plates were respread. Figure 7 demonstrates that the multiple units formed within the "giant" cysts are viable cells.