During the aerobic growth of Streptococcus faecalis strain 10C1, with limiting levels of glucose as the substrate, a molar growth yield (Y) of 58.2 g (dry weight) per mole of glucose was obtained. Under these conditions of growth, glucose was dissimilated primarily to acetate and CO 2 . The incorporation of 14 C-glucose into cell material was no greater under aerobic conditions than during anaerobic growth. Assuming an adenosine triphosphate coefficient of 10.5, the aerobic Y cannot be explained solely on the basis of substrate phosphorylation and would appear to substantiate previous enzymatic evidence for oxidative phosphorylation in this cytochromeless species. With mannitol as the substrate, an aerobic Y of 64.6 was obtained. Extracts of mannitol-grown cells contained a nicotinamide adenine dinucleotide (NAD)-linked mannitol-1-phosphate (M-1-P) dehydrogenase. The difference in aerobic Y values with mannitol and glucose as substrates would indicate that the in vivo P/O ratio from the oxidation of reduced NAD generated by the oxidation of M-1-P approximates 0.6. The Y values with pyruvate and glycerol as substrates under aerobic conditions were 15.5 and 24.7, respectively.

SUMMARYA complex tissue culture medium supplemented with swine serum and peptone supported optimal growth of Mycoplasma gallisepticum strain 293. Media lacking any of these components supported little or no growth. However, when 5'-monophosphate nucleotides replaced the peptone growth was supported. The minimal nucleotides necessary to support good growth were adenylic, cytidylic, guanylic and thymidylic acids. I n some cases the addition of the four ribonucleotides and the four deoxyribonucleotides in place of peptone improved growth; the four ribonucleotides alone supported poor growth. Thymidylic acid seemed essential for growth, and uridylic acid appeared to be inhibitory.The mixture of ribonucleosides and deoxyribonucleosides, but not of purines and pyrimidines, when substituted for the peptone, also supported good growth. The concentrations of nucleosides and nucleotides had a significant effect on growth. Although the nutritional factors of swine serum were not defined, the effects of different sera on growth were investigated. Rabbit, horse, turkey and swine serum supported optimum growth; human serum supported less, whereas PPLO serum fraction (Difco) or bovine serum supported poor growth. Dog serum did not support growth.

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Studies on the respiratory pathways among the mycoplasma have been largely limited to the effects of various inhibitors and the presence or absence of the enzyme catalase in these organisms. The advent of more sophisticated investigations on the respiratory chain and of the terminal energy-generating mechanisms has undoubtedly been delayed by the difficulties of mass culture and the resulting limitation in the application of conventional techniques for the study of respiratory enzymes to this microbial group.Studies by Pirie (1938), Kandler and Kandler (1955), Kandler et al. (1956), Weibull and Hammarberg ( 1963) and Low et al. (1965) would indicate that a high percentage of mycoplasma species lack the heme-type respiratory enzymes including the enzyme catalase.In our laboratory, lactate oxidation by Mycoplasma gallisepticum (Smith, Van Demark and Fabricant, 1963) was found to be insensitive to the conventional inhibitors of the heme-containing respiratory carriers, including sodium cyanide, sodium azide and carbon monoxide. The benzidine test for heme-containing compounds as well as spectrophotometric assays for catalase and the cytochromes were negative. The Role of FlavoproteinsIndicative of the function of flavoproteins in the respiration of this species was the stimulation of lactate oxidation by the addition of flavin adenine mononucleotide (FMN) or flavin adenine dinucleotide (FAD) to resting cell suspension, as well as the sensitivity of this oxidation to conventional flavin-inhibitors, e.g., atabrine. Spectrophotometric assays of extracts of M . gallisepticum for flavins gave average flavin levels of 2.1 X moles/mg of cell dry weight. Relatively speaking, this flavin level is high, analogous to that found in microorganisms whose respiratory chain is flavin-terminated, e.g., the lactic acid bacteria.In manometric studies, it was observed that the rate of lactate oxidation by M . gallisepticum increased with increasing oxygen tension, indicating a low affinity of the terminal respiratory sites of this species for atmospheric oxygen, which is characteristic of a flavin-terminated respiratory system. Among the flavin-linked respiratory enzymes found in this species were a nicotinamide adenine dinucleotide (NAD)-specific lactic dehydrogenase. No cytochrome c reductase or reduced nicotinamide adenine dinucleotide (NADH) peroxidase activity were detected.Thus the respiratory pathways of M . gallisepticum and a high percentage of other mycoplasma species appear similar in nature to the Lactobacillaceae, as they lack the heme-containing enzymes, and their respiratory chain is flavin-terminated. However, the possible presence of naphthoquinones in the respiratory chain of these mycoplasma species remains to be investigated.

The uptake of '4C-a-methyl-D-glucoside (aMG) by washed cells of Mycoplasma strain Y was found to be dependent on the supply of metabolic energy. Glycerol or D-mannose, but not L-lactate, would serve as an energy source. Uptake was inhibited by fluoride, iodoacetate, and arsenate, but not by 2,4dinitrophenol. D-Glucose was inhibitory, presumably by competing for the transport system. The initial product of accumulation had the properties of a phosphate ester of aMG. The proportion of free aMG in the cells increased with time, until a steady state was reached in which uptake was balanced by the efflux of free aMG from the cells. Broken-cell preparations catalyzed a phosphoenolpyruvate-dependent phosphorylation of aMG and of D-glucose.