Respiratory Pathways in the Mycoplasma*

Abstract

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.

Hemolysin and Peroxide Activity ofMycoplasmaSpecies

“…There was some evidence to suggest that the presence of AT resulted in a slight increase in peroxide activity. This may have resulted from the destruction of small amounts of catalase which may have been produced by the mycoplasma cells; catalase production by mycoplasma has been reported by some workers (17,22,27,28).…”

“…The benzidine-blood reaction is based upon the formation of a colored complex resulting from the combination of benzidine and hemin in the presence of peroxide. This reaction has been used to detect the presence of hemins (19) and more recently heme-containing enzymes of mycoplasma (27). This investigation explores the value of the benzidine reaction in the detection of peroxide production by mycoplasma.…”

Complexity of the Mycoplasma fermentans M64 Genome and Metabolic Essentiality and Diversity among Mycoplasmas

“…All of the Mycoplasma species exhibited conserved energy metabolism-related genes including genes encoding NADH dehydrogenase and F-type ATPase aside from cytochrome-containing complex, indicating a truncated electron transport chain. Thus, the ATP generation proceeds via inefficient substrate-level phosphorylation in the flavin-terminated respiratory pathway rather than oxidative phosphorylation [59], [60], [61]. In addition, the pentose phosphate pathway, an alternative to glycolysis, may generate NADPH for reductive biosynthesis reactions in Mycoplasma species.…”

Anaeroplasma abactoclasticum gen.nov., sp.nov.: an Obligately Anaerobic Mycoplasma from the Rumen

“…The obligately anaerobic nature of the mycoplasmas reported here distinguishes them from other mycoplasmas that have been described previously, although mycoplasmas that require reduced oxygen tension for initial isolation but lose this requirement upon repeated subculture have been described (24,27). Strictly anaerobic conditions are required for the growth of the organisms described in this study even though they have been transferred more than 50 times over a 2-year period.…”