Summary: The production of filamentous forms of Clostridium welchii which occurs in complex media containing certain commercial and chemically treated peptones is due to a deficiency of ionized magnesium. Such filaments revert to cells of normal morphological appearance on subculture in a medium containing free magnesium ions, but the change cannot be brought about by the presence of metallic ions other than magnesium. It is, therefore, suggested that the latter is essential for the activity of the cell-dividing mechanism.
The presence of a growth-inhibitory factor in certain peptones has been established. The active agent appears to be a fatty acid and may be extracted from acidified peptone solutions with ether or chloroform. The presence of the inhibitory substance in peptone markedly decreases the crop yield of Cl. welchii but has no direct influence on the production of filaments.
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