The endogenous respiration of microorganisms.

In respiration studies and work on oxidative asimilation by microorganisms it is often of interest to know whether or not the endogenous respiration continues in the presence of an external substrate. Indirect methods, such as those first described by Barker (1936), have frequently been used in attempts to answer this question, but they are not entirely satisfactory. A more direct approach has been made recently by the use of cells which have incorporated C14, so that the carbon dioxide produced by endogenous respiration is radioactive. An unlabeled substrate is then added, and the total radioactivity of the carbon dioxide produced is determined. This carbon dioxide should be inactive if the endogenous respiration is completely suppressed by the added substrate. Experiments of this type with the green alga Chlorella vulgaris, the fungus Zygorhyncus moelleri, and baker's yeast are reported here.