A Cultural Study of Certain Anaerobic Butyric-Acid-Forming Bacteria

Abstract

The anaerobic butyric-acid-forming bacteria constitute a large and complex group. Perhaps the production of butyric acid is their salient characteristic, although it is not a distinguishing characteristic for there are aerobic and facultative organisms which also produce butyric acid. Only the obligate anaerobes produce it in significant quantities, however; they may form the acid in any of the following ways : by fermentation of carbohydrates, polyhydric alcohols, and glucosides; by fermentation of calcium lactate or other lactates ; or by degradation of proteins and derived compounds. Pasteur23 in 1862 discovered an anaerobic organism in a spontaneous fermentation of calcium lactate. He found butyric acid among the fermentation products and suggested that in the .butyric fermentation, lactic acid might be intermediate between the 6-carbon sugar and the 4-carbon butyric acid. This scheme of the mechanism of fermentation is now in disrepute and is of historical interest only. It is noteworthy, however, that several of the cultures described in the early work on butyric fermentation were said to ferment calcium lactate; e. g., Vibrion butyriqueof Pasteur, Granulobacter lactobutyricus of Beijerinck,2 certain of Bredemann's6 strains, and one organism of Schattenfroh and Grassberger.28 Production of butyric acid from protein and its split-products can never be very extensive ; it may account for the acid produced by certain pathogenic anaerobes in carbohydrate poor medium. Certain of these organisms like B. putrificus of Bienstock6 are reported to be so specialized as to ferment no carbohydrates and to require complex protein medium. B. tetani is another typically non-fermentative organism producing small amounts of butyric acid among its metabolic products (Chudiakow9). The fermentation of carbohydrates then is the most important means of producing butyric acid. Many of the butyric organisms obtain their energy and oxygen by this anaerobic decomposition of carbohydrates alone. Others which ordinarily are carbohydrate-fermenting may live in carbohydrate-free medium by attacking proteins and protein split-products. If the discussion be limited to the strictly anaerobic butyric acid-producing organisms, the definition of the group might be anaerobic, motile, spore-forming organisms of the genus Clostridium, producing butyric acid by any of the above mentioned means. This definition would include certain pathogenic anaerobes? CI. welchii, CI. tetani, even CI. botulinum. These are not the type of butyrics associated with fermentation. Therefore, the butyric anaerobes of fermentation