BACTERIA FIXING ATMOSPHERIC NITROGEN 119 



The reproductive organs of Azotobacter are : 



1. Gonidia, in part filterable, produced in the cell. 



2. Regenerative bodies and exospores, either produced by the cells or growing 



up from the symplasm. 



3. Arthrospores formed by fragmentation of the rod-like or fungoid cells. 



4. Mycrocysts, globular or oval resting cells. 



5. Endospores, produced singly by the rod-like cells in terminal or in central 



position, or in the form of two or more globular or spindle-shaped spo- 

 rangia. 

 Gonidia form the basis for the development of regenerative bodies, arthro- 

 spores and endospores. Symplasm formation and regeneration of new cells 

 proceeds with Azotobacter as with other bacteria. 72 



Physiology of Azotobacter. There is an important difference in the 

 amount of nitrogen fixed by pure cultures of the organism and by- 

 crude cultures in the presence of other organisms, in favor of the last. 

 This was first recognized by Beijerinck and Van Delden, who went as 

 far as to state that A. chroococcum is incapable of fixing any appreciable 

 quantities of nitrogen, when growing in pure culture, but large amounts 

 of nitrogen are fixed in the presence of the spore bearing Granulobacter 

 or non-spore bearing members of the B. aerogenes group and B. radiobac- 

 ter. Members of the Granulobacter group were found capable of fixing 

 nitrogen by themselves, this power becoming very pronounced in the 

 presence of Azotobacter. On the other hand, Gerlach and Vogel 73 

 proved conclusively that A . chroococcum is able to fix large quantities of 

 atmospheric nitrogen when grown in pure culture, in the presence of 

 salts of organic acids or sugar. This was soon confirmed by others. 74,75 

 The presence of other organisms, however, is advantageous to the 

 amount of nitrogen fixed and the rate of fixation, either by using up the 

 waste products or creating otherwise favorable conditions. Young 

 cultures will fix more nitrogen than old cultures; crude cultures more 

 than pure cultures. 



A number of hexoses (glucose best), pentoses, alcohols (mannite) 

 and salts of organic acids, such as malate, 76 lactate, butyrate, succinate, 



72 On the systematic position of Azotobacter, the work of Lohnis and Hanzawa 

 should be consulted. Lohnis, F., and Hanzawa, J. Die Stellung von Azotobacter 

 im System. Centrbl. Bakt. II, 42: 1-8. 1914. 



73 Gerlach, M., and Vogel, I. Stickstoffsammelnde Bakterien. Centrbl. 

 Bakt. 8: 669-674. 1902; 9: 817-821, 881-892. 1902; 10: 363-643. 1903. 



74 Freudenreich, 1903 (p. 113). 



75 Lipman, 1903 (p. 115). 



76 Beijerinck, M. W. Uber ein Spirillum, welches freien Stickstoff binden 

 kann? Centrbl. Bakt. II, 63: 353-359. 1925. 



