Bacterial Cell Metabolism under Anaerobic Conditions

Escherichia coli has been cultivated in a peptone water medium saturated continuously with nitrogen by use of a gas train so as to produce anaerobic conditions. Under these circumstances growth was greatly inhibited. Cultures which originally contained 11 million bacteria per cc. showed on the average only 32 million after 5 hours (as compared with 655 million in similar cultures saturated with air). The metabolic activity of the cells in such a culture was greatly reduced by the anaerobic conditions. It actually fell off from 42 mg. x 10(-11) per cell per hour during the 1st hour to 27 mg. during the 2nd hour and rose only to a maximum of 68 during the 3rd hour. Similar cultures saturated with air showed a rise from 37 mg. x 10(-11) during the 1st hour to 123 during the 2nd hour. The addition of glucose to the medium, under aerobic conditions, has been shown in previous studies to cause only a slight increase in bacterial numbers (861 instead of 655 million after the 5th hour). In the cultures aerated with nitrogen, the addition of glucose has no effect during the first hours. There is again a long lag period and a reduced metabolic rate. After the 2nd hour, however, a wholly different phenomenon manifests itself. The bacterial population increases more rapidly than in the anaerobic peptone medium (reaching a maximum of 142 million after 5 hours). This growth is accompanied by an enormous increase in the rate of CO(2) yield, which reaches 211 mg. x 10(-11) per cell per hour during the 4th hour (nearly double the maximum values recorded under aerobic conditions). The same phenomenon is, of course, illustrated by the enormous yield of CO(2) produced by the action of fermenting organisms in carbohydrate media recorded by Anderson (1924) and other students of the obligate anaerobes. We have here, however, a somewhat striking illustration of the distinct type of metabolic activity manifested by a facultative organism under anaerobic conditions in the presence of sugar measured on a cell-per-hour basis. This is a quantitative illustration of the "life without air" described by Pasteur.