Audrey F. Gronlund

ENDOGENOUS METABOLISM OF PSEUDOMONAS

Because of the quantitative importance of the endogenous respiration of obligate aerobic bacteria, it has been usual to attempt to reduce the reserve materials in the cells and to correct for the endogenous activity that might continue during substrate oxidation. Some of the accepted techniques for lowering endogenous respiration were applied to Pseudomonm aeruginosa ATCC 9027. It was found that regardless of the growth medium, resting cell suspensions exhibited a high rate of endogenous activity as measured by oxygen uptake studies. It was also found that cells harvested from the logarithmic growth phase exhibited the same rate of endogenous oxygen uptake as cells from the stationary phase. Aeration of resting cell suspensions for six hours or storage for up to five days in ice, followed by centrifugation of the cells and resuspension in fresh phosphate buffer, did not decrease the rate of endogenous oxygen uptake (TABLE 1). In fact the rate of respiration increased in spite of a pronounced decrease in the number of viable cells as determined by the Standard Methods Plate Count. One might conclude from all of these observations that the substrate or substrates of endogenous respiration are present in maximum concentration, even in cells that are in the logarithmic growth phase; that one cannot grow cells that are devoid of this reserve substrate; and that starvation of the cells does not specifically reduce the reserves. The material which most readily fulfills all of these criteria is some constituent essential to the cell or the entire cellular protoplasm. One might further conclude that the phenomenon of endogenous respiration in P . aeruginosa is merely the attrition of the cell as it is forced to oxidize some of its normal cellular constituents.