Studies in Bacterial Metabolism. Vii. by Arthur

A most fundamental principle of bacterial metabolism may be expressed concisely by stating that “Fermentation takes precedence over putrefaction;“’ that is to say, bacteria in general which can utilize both carbohydrate and protein, act upon the former in preference to the latter when bot,h are present in the same medium. In view of the confusion attending the use of the terms putrefaction and fermentation, they must be sharply defined. By fermentation is meant “the action of microorganisms upon carbohydrate,’ and by putrefaction is meant “the action of microbrganisms upon nitrogenous substances.“2 Bacteria in common with all known living things need nitrogen to build up their bodies; it is self-evident, therefore, that even when carbohydrate is being fermented, enough protein must be broken down to satisfy their nitrogen requirements. Bacterial activity, therefore, must be sharply differentiated into two distinct processes, the structural and the vegetative, both functions being essential for their metabolism. Nitrogen is indispensable for the structural process, hence bacteria must have nitrogen in their dietary. With the vast majority of bacteria, however, the vegetative process may be satisfied either by utilizable carbohydrate or by protein. Whenever bacteria can utilize both carbohydrate and protein for their vegetative activity (for fuel) and both are present in the medium in which these