Okrend, Harold (Rutgers, The State University, New Brunswick, N.J.), and Norman C. Dondero . Requirement of Sphaerotilus for cyanocobalamin. J. Bacteriol. 87: 286–292. 1964.—Cultures of Sphaerotilus grew well in a culture medium containing pancreatic digest of casein, glycerol, and yeast autolysate, but grew poorly in a defined medium containing monosodium glutamate, glycerol, and salts. Measurement of dry weight, cell nitrogen, and deoxyribonucleic acid showed that the addition of 1.0 mμg/ml of cyancobalamin to the defined medium gave growth equivalent to that obtained with the pancreatic digest of casein. Methionine, in a concentration of 2 × 10 4 -fold, relieved the requirement for cyanocobalamin, but cobalt did not replace cyanocobalamin nor stimulate growth. Of 38 additional cultures of diverse origin, 19 showed stimulation by visible comparison of growth in tubes; nonquantitative comparisons, however, were not reliable for showing differences in growth of this organism.