SECTION D 



1. Organisms contain photosynthetic pigments alone or with carotenoid pigments. Cells 



in masses appear green to greenish yellow or red to purple. These organisms will grow 

 in certain media under anaerobic conditions only when exposed to light. Certain 



species are also capable of aerobic growth in the dark 29 



Not as above 2 



2. Single cells borne on the end of elongated stalks; aquatic forms 3 



Cells not borne on stalks 4 



3. Stalks band-shaped and twisted into a flat spiral; dumb-bell shaped in cross section; 



composed entirely of or impregnated with ferric hydroxide; dissolves completely in 

 dilute mineral acids; a single cell is borne at the end of each stalk 



Gallionella p. 2H 



Stalks long and slender; attached to some solid object by means of a holdfast; cells 



spherical to pear-shaped; reproduce by budding, the daughter cells subsequently 



secreting individual stalks Blastocaulis p. 279 



4. Cells or their capsules impregnated with iron or manganese 5 



Note: In the absence of further information, these organisms are identified on 

 their iron-depositing characteristics. Most iron organisms studied in pure cul- 

 ture metabolize the organic compound which forms the iron chelate, and the 

 liberated iron chelates with some cell component. Citrate-utilizing organisms 

 will, for example, release iron from ferric ammonium citrate. Accumulation of 

 the iron in or on the cell may depend only on the nature of the cell substance. 

 Pure-culture studies may place these organisms in more commonly recognized 

 genera. Many more organisms, if tested, may fall into the following genera. 

 They should also be treated as non-iron-depositing cells and should be fol- 

 lowed through the key. 

 Not as above 7 



5. Not encapsulated Siderococcus p. 225 



Cells encapsulated 6 



6. Groups of cocci arranged in pairs in a common capsule. . . . Siderosphaera p. 220 

 Cocci occur singlj^ or in unordered groups in a common capsule 



Siderocapsa p. 218 



7. Cells coccal only as a stage in a definite life cycle or as a pleomorphic phase of rod- 



shaped bacteria 8 



Cells coccal at all stages of growth 15 



8. Cells have a definite cyclic form of development; spherical cells germinate at one or 



more points to produce rod-shaped cells which elongate and divide. At the point of 

 division, growth of the cells continues at an angle to the original axis. When the 

 side branch is equal in size to the parent cell, division occurs at the angle. This process 

 is repeated during the growth of the colony. In older colonies, the rods transform en- 

 tirely into a mass of cocci. Rods are most frequently Gram-negative with Gram- 

 positive granules; cocci are frequently Gram -positive; soil inhabitants. 



Arthrobacter p. 605 

 Note: The emphasis lies on the final transformation into cocci. Some authori- 

 ties may consider that limited true branching may occur. If this is admitted, 

 the dividing line between Arthrobacter and Nocardia becomes very slim. The 

 author's observations of Arthrobacter globiforme fit the above statement, and 

 it is suggested that these criteria be adopted, true branching forms which later 

 disintegrate being assigned to Nocardia. 

 Not as above 9 



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