QUALITATIVE STUDIES OF SOIL MICROORGANISMS X

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Abstract
The indigenous bacteria of soil include a group of organisms dependent on soil extract for growth and unable to develop in media containing inorganic salts and sugars, supplemented by yeast extract or combinations of amino acids and vitamins (not including B12)- For the majority of the organisms dependent upon essential growth factors supplied by soil extract, the growth-promoting effect of the latter could be replaced by vitamin B12 (crystalline), the most significant range of effectiveness lying between concns. of 0.01 and 1 m[mu]g./ml. Cobalt (Co++) was unable to replace the vitamin in the nutrition of the bacteria requiring Bj2- Various other soil bacteria having simple nutritional requirements were able to synthesize a growth promoting factor, the nutrilite effect of which was related to the amount of B12 produced, with a critical concentration of approx. 0.075 m[mu]g. of the vitamin per ml. for growth of the test bacteria. The results indicate that the requirement for vitamin B12 or its physiological equivalent is by no means restricted to small groups of organisms, but is shown by an important ecological group of bacteria comprising part of the microflora of the soil.