COMPREHENSIVE KEY 995 



39. Cells coccoid only at pH 7.0 on peptone yeast extract acetate agar; develop into multi- 



cellular rods with peritrichous flagella under other conditions; do not fix atmospheric 



nitrogen Caryophanon p. 831 



Cells grow in nitrogen-free mineral salts media, fixing atmospheric nitrogen 



Azotobacter p. 283 



40. Aerobic 41 



Anaerobic 42 



41. Gram -positive; cells occur in irregular clusters Micrococcus p. 455 



Gram-negative; fix atmospheric nitrogen. The coccoid form is only part of a cycle 



of morphological forms, the initial stage of which is a large rod 



Azotobacter p. 283 



42. Large cocci, 3 to 4 microns wide, sometimes bearing rod-shaped protuberances on op- 



posite sides and at an obtuse angle to one another — a pleomorphic stage of a rod- 

 shaped cell 0.8 by 2.4 to 10 microns; produce copious gas from peptone 



Sphaerophorus -p. 44i 

 {S. ridiculosis) 

 Spherical cells; pleomorphic, ranging in diameter from 0.7 to 2.5 microns; occurring in 

 pairs, short chains and in irregular groups; dependent on glycine for growth in or- 

 ganic media. Glycine is decomposed to CO2 , NH3 and acetic acid 



Peptococcus p. 474 

 {P. (jlycinophilus) 



43. Large, cj'lindrical, pear-shaped or slightly curved rods 3 to 14 microns wide; activelj^ 



motile by means of single polar flagella; contain large spherules of calcium carbonate 



and may also contain sulfur Macromonas p. 80 



Not as above 44 



44. Curved rods 45 



Straight rods 46 



45. Curved rods with a bunch of flagella inserted laterally in the concave part of the cell; 



anaerobic; recorded from the cecum of the guinea pig, the buccal cavity of man and 



the rumen of the herbivora Selenomonas p. 258 



Curved rods with polar flagella; 1.7 to 2.4 by 6.6 to 14.0 microns; contain small globules 

 of sulfur in the center of the cell and a single large volutin granule at each end 



Thiospira p. 82 



46. Cells 1.4 to 2.0 by 4.0 to 5.0 microns; motile by means of polar flagella; anaerobic to 



microaerophilic; ferments glucose, producing ethyl alcohol, carbon dioxide and 



lactic acid Zymonionas p. 199 



Motile by means of peritrichous flagella; grow in a nitrogen-free mineral salts medium, 

 fixing atmospheric nitrogen Azotobacter p. 283 



