OXIDATIVE ASSIMILATION BY PSEUDOMONAS SACCHAROPHILA WITH C14-LABELED SUBSTRATES

In 1936, Barker discovered that during the oxidation of many organic compounds by resting cells of colorless alga Prototheca zopfii, a large part of the substrate undergoes "oxidative assimilation," and becomes converted to organic material within the cell. Since then, the occurrence of massive assimilation has been confirmed for many other microorganisms and for a wide variety of substrates; and it has been shown that the phenomenon occurs during fermentations as well as oxidations, by both resting and growing cells (Clifton, 1946). Heretofore, the techniques used for the detailed study of the assimilatory process have been largely manometric, in some cases accompanied by gross material balances; despite the considerable volume of work undertaken, the somewhat indirect nature of these experimental approaches has made it impossible to draw any but the most tentative conclusions concerning the mechanism of assimilation. Baddiley et al. (1950) have used labeled acetate in the studies of assimilatory processes of growing yeast. In the present studies, several labeled substrates were used in an attempt to determine the metabolic fate of the individual carbon atoms in these compounds during their oxidation by resting cell suspensions of Pseudomonas saccharophila. In addition, it was found possible to obtain direct evidence concerning the effect of the oxidation of exogenous substrates on the endogenous respiration. The results are in general agreement with earlier, tentative conclusions based on the use of less direct methods.