NUTRITION OF A COBALAMIN-REQUIRING SOIL BACTERIUM

Abstract

The pattern of the vitamin B₁₂ requirement of a soil bacterium "Lochhead 38" (provisionally assigned to Arthrobacter) resembled that of the protozoan Ochromonas malhamensis and of higher animals. Of the naturally-occurring B₁₂-vitamins, cyanocobalamin and vitamin B_12III are active. Pseudovitamin B₁₂ and Factor A have very little or no intrinsic activity, and when present in relatively high concentrations both compounds depress the rate of the growth response to limiting cyanocobalamin. Factor B, the porphyrin-like nucleus of the vitamin B₁₂ molecule without the nucleotide, is inactive, as are also methionine and deoxyribosides. A disadvantage in the use of Lochhead 38 for assay purposes is that in vitamin-B₁₂-dehcient cultures the organisms flocculate.