SECTION F 



1. Pear-shaped cells; 1.0 to 2.0 by 4.0 to 5.0 microns; non-motile; grow attached to each 



other or to solid surfaces by a holdfast secreted from the narrow end; sessile; multiply 



by longitudinal fission and by budding at the free end Pasteuria p. 279 



Not as above 2 



2. Curved or straight rods which produce a well -differentiated stalk by which they may 



attach to a surface; a single cell occurs at the end of each stalk except during the 



process of multiplication 3 



Not as above 6 



3. Cells curved; stalk produced as a continuation of the cell wall parallel to the long axis 



of the cell; reproduction by transverse fission of the cell from the free end, the daugh- 

 ter cell developing a single polar flagellum, then breaking away and producing a 

 stalk from the end of the cell at which the flagellum is located 



Caulobacter -p. 213 

 Not as above; cells produce a stalk at right angles to the main axis of the cell 4 



4. Large rods, 2.0 by 6.0 to 12.0 microns, borne on the ends of lobose, dichotomously 



branched stalks composed of gum, forming a gummy colony which floats on water; 



may become attached Nevskia p. 216 



Not as above; stalks composed of or impregnated with ferric hydroxide; dissolve com- 

 pletely in hydrochloric acid; cells curved with the stalk secreted from the concave 

 side ; reported only from iron-bearing waters 5 



5. Stalks ribbon-like and usually twisted; cells located terminally 



Gallionella p. 2U 

 Stalks horn-shaped; not twisted; round in cross section Siderophacus p. 216 



6. Obligate autotrophes which oxidize ferrous to ferric iron at low pH in mineral synthetic 



media ; Gram-negative rods 7 



Not as above 8 



7. Thiosulfate is oxidized Thiobacillus p. 83 



{T. ferrooxidans) 



Thiosulfate is not oxidized Ferrobacillus p. 227 



(F. ferrooxidans) 



8. Organisms which store oxides of manganese or iron either in the cell membrane, in the 



cell wall or in the surrounding capsules; found in water and mud 9 



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

 on the basis of their iron-depositing characteristics. Most iron organisms 

 studied in pure culture metabolize the organic compound which forms the 

 iron chelate, and the liberated iron then chelates with some cell component. 

 Citrate-utilizing organisms will, for example, release iron from ferric ammo- 

 nium 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 or- 

 ganisms in more commonly recognized genera. They should also be treated 

 as non-iron-depositing cells and should be followed through the key. 

 Not as above 13 



9. Cells encapsulated or embedded in mucus or surrounded by a torus of iron 10 



Not as above; iron or manganese stored in cell membrane or cell wall 



Siderobacter p. 226 



10. Encapsulated cells occurring singly or in short chains, each capsule being completely 



surrounded by a ring (torus) heavily impregnated with iron or manganese giving the 



general appearance of links in a chain Naumanniella p. 223 



Not as above 11 



11. Cells surrounded by a ring (torus) which is open at one end; cells motile by means of 



two unequal polar flagella Ochrobium p. 225 



1005 



