For many years bacteriologists have observed that some bacteria produce acid from carbohy-drates only under aerobic conditions while others produce acid both under aerobic and anaerobic conditions. The significance of these observations does not seem to have been appreciated generally by taxonomists. Studies of bacterial physiology have made it increasingly evident that the bac-terial metabolism of carbohydrates may be ac-complished by two apparently fundamentally different mechanisms (see for example Porter, 1946; Werkman and Wilson, 1951). By one mechanism, appropriately called fermentation, the glucose molecule first is phosphorylated and then split into two triose molecules which undergo further changes. This process is independent of oxygen. By the other mechanism, which we shall call oxidation, the glucose molecule is not split into two triose molecules, but the aldehyde group is oxidized to a carboxyl group forming gluconic acid. Further oxidation may take place to form various products such as 2-ketogluconic acid. Several studies of this mechanism, summarized by Sebek and Randles (1952), have failed to detect phosphorylation of the glucose molecule preliminary to oxidation. In the absence of com-pounds such as nitrates, the oxidation of carbo-hydrates is a strictly aerobic process, whereas fermentation is an anaerobic process.
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