A STUDY OF LARGE BODIES IN AZOTOBACTER AGILE

Abstract

In the course of cytological studies of the genus Azotobacter, large bodies, buds, L colonies, and other peculiarities were observed in one particular strain, Azoto-bacter agile M.B. 4.4. The balloon shapes that have received attention in recent literature (Dienes, 1946; Shanahan et al., 1947; Tulasne, 1949a) were especially abundant among these morphological oddities. It should be emphasized that, unlike other strains of Azotobacter (Eisenstark et al., 1950), variety A. agile M.B. 4.4 does not go into an encysted stage. This strain is morphologically stable and rarely varies from the typical single and paired forms (figures 1 and 2) when grown on the usual laboratory nitrogen-free media. Even very old cultures contain only these regular cell types. However, when cells are transferred from a nitrogen-free medium to a medium containing beef extract or soil extract, giant cells develop in abundant numbers within 24 hours. Further study indicates that a few toxic substances may produce the same results. MATERIALS AND METHODS The organism used in this study was Azotobacter agile M.B. 4.4, obtained from Professor C. B. van Niel. This organism has been used in research on biochemical mutants (Karlsson and Barker, 1948), and it was for this reason that its cytology was of interest to the present investigators. The basal medium used in this study contained only inorganic salts, glucose, agar, and distilled water (Karlsson and Barker, 1948). Standard nutrient agar and soil extract agar (Allen, 1949) were used to obtain the large forms. Cells were examined by standard procedures of phase microscopy, electron microscopy, and nuclear staining. In order to test for possible single nutritional substances that might stimulate the production of large forms, the following carbon compounds, amino acids, and accessory growth substances were added to the basal medium during the course of experiments: glycine, aspartic acid, glutamic acid, asparagine, KNO3