COMPREHENSIVE KEY 997 



Colorless cells, ovoid, 0.5 by 1.0 micron when mature; motile by means of a single 

 polar flagellum; daughter cells may break loose from the tubular outgrowth and 

 form tubes of their own while still actively motile. .Hyphoinicrobium p. 2'^1 



Cell masses salmon-pink to a deep orange-red; cells ovoid, 1.2 by 2.S microns; 

 non-motile; contain photosynthetic pigments; grow only under anaerobic condi- 

 tions when exposed to light Rhodoniicrohium p. 2^^ 



6. Spherical cells which reproduce by binary fission or by budding. Well-defined stalks are 



secreted by some species, the budding form of reproduction being confined to the 

 stalked types; proceed to .Section D p. 1000 



7. Vegetative cells, rod-shaped; Gram-negative; microcjsts produced in macroscopically 



visible fruiting bodies or occur loosely among elongated S-shaped, twisted or straight 

 flexible Gram-negative rods; germinate to produce rod-shaped cells which are motile 

 only by a creeping action on solid surfaces. These rods may contract to form spherical 

 microcysts or may combine in groups to form fruiting bodies in which the spherical 

 or rod-shaped microcysts are formed. See Manual keys for the order Myxobac- 

 terales p. 85S 



8. Rod-shaped cells, 0.5 to 1.5 by 2 to 5 microns, which grow in colonies on the surface of 



water containing sulfide and which deposit sulfur either inside or outside the cells. 

 One species forms bladder-like gelatinous colonies with the bacteria embedded in the 



surface Thiobacterium p. 79 



Note: This very ill-defined group is separated here because of a complete lack 

 of information of other properties. It is suggested that any such forms, if found, 

 should be keyed out in the section on rods to determine their possible taxonomic 

 relationship. The presence of the sulfur around the cells in such a location may 

 not be significant. 



9. Rod-shaped and filamentous forms reproducing by binary fission, by fragmentation 



of the mycelium, by the production of endospores or conidia or by the production of 

 microcysts; proceed to Section E p. lOOS 



