J. Murray Luck

The Role of Bacteria in the Nutrition of Protozoa

A CCORDING to Calkins (i) four principal types of nutrition are to be found among the protozoa. Some are holozoic or holophytic, dependent for maintenance upon other living organisms as sources of food. Others have developed a saprozoic or saprophytic mode of nutrition and are able to live on dead organisms or the products of their disintegration. A third group is autotrophic. The presence of a photosynthetic pigment permits the organism to utilize the energy of sunlight in the elaboration of complex tissue constituents from the simplest of raw materials. Finally there are heterotrophic protozoa which are able, as has been fairly well demonstrated, to live both saprophytic and autotrophic modes of existence. Many colored flagellates are autotrophic in light and saprophytic in the dark. In fact the saprophytic flagellates are conceivably derived from heterotrophs by loss of the photosynthetic pigment. In this paper we propose to confine our attention to nutrition of the first two types and, in particular, we shall enquire into that knotty problem of forcing a normally holozoic animal to lead a saprophytic existence. Our purpose in so doing is not only to attempt the teaching of new tricks to the protozoa. Nor do we care merely to assist in unravelling the threads of inter-related fact that are so confusingly tangled in the baffling problems of holozoic nutrition, even though a satisfying explanation of these phenomena would constitute one of the most fundamental contributions to our knowledge of nutrition. Rather, we have found ourselves lured on by an objective of different and perhaps more immediate consequence. It is our intention to study the chemistry of protozoan metabolism, the nature and significance of those elementary and molecular constituents of protoplasm, which though present in very small quantities are nevertheless indispensable for the maintenance and well-being of the organism, the nature and mode of action of toxic agents, the effects of radiation of high intensity, in short a number of problems which demand that the protozoon under investigation be unaccompanied by other living forms. If a normally holozoic organism is to be studied along these lines it is apparent that the creature must, if possible, be led into the ways of its saprophytic cousins.

Effect of sympathomimetic amines upon amino acid nitrogen content of the blood.

Conclusion From the data obtained it is seen that only epinephrine displays the ability to lower the blood amino acid nitrogen. This confirms the observations of Luck and associates 9 10 11 . While 3 out of 4 rabbits displayed a moderate increase in amino acid N following phenylethylamine administration, the significance of this is not apparent. The fluctuations obtained with the other sympathomimetic drugs are not great enough to exclude experimental error.

Effect of proteins on the diffusion of amino acids through membranes.

The concentration of amino acids in nucleated erythrocytes is known to be several times that of the surrounding plasma. The concentration in mammalian liver and muscle, as indicated by determinations on tungstic acid extracts, is 6 to 8 times that of the blood plasma. As part of an inquiry into the factors that cause this inequality in distribution we have studied the diffusion of amino acids through tubular membranes of cellophane. The progress of dialysis was measured by amino nitrogen determinations on the inner and outer liquids by the manometric method of Van Slyke. The inner liquid consisted of a 1.5% solution of gold label gelatin. The amino acid was contained in the outer liquid in an initial concentration of 0.001 N. Glycine was generally employed. After 15 to 30 hours at a temperature of 20° the experiments were terminated. The outer fluid was analyzed directly, while the inner fluid was first rendered free of protein by treatment with phosphotungstic acid. Over a wide range of H ion concentration, (pH 2.5-9.5) the equilibrium concentration of amino acid in the outer fluid was found to be over twice as great as that in the inner protein-containing solution. This inequality persisted, undiminished in magnitude, even in the isoelectric zone of the protein. The equilibrium, moreover, could be approached from the other end, that is by dissolving the amino acid in the inner fluid containing the dispersed protein. In neutral solutions aspartic acid and glutamic acid behaved like glycine in the establishment of a high concentration ratio when dialyzed against 1.5% gelatin. Dialyzed solutions of crystalline egg albumin (1.5%) and agar-agar (0.38%) affected the diffusion of glycine at pH 5 in similar fashion.