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Metabolic Activity of the Trench Fever Rickettsia, Rickettsia quintana

Department of Microbiology, Naval Medical Research Institute, Bethesda, Maryland

ABSTRACT

A study of the metabolic activity of Rickettsia quintana was carried out by conventional Warburg and radioisotope techniques with intact cells harvested while growing in the fluid counterpart of the medium of Vinson and Fuller. Like other rickettsiae, R. quintana did not utilize glucose, but did metabolize glutamate and glutamine. Unlike typhus rickettsiae, R. quintana did not require a diluent high in K⁺ for metabolic activity, and it utilized glutamine more efficiently than glutamate. In typical experiments, this microorganism produced 1.6 to 2.0 µmoles of CO₂ from glutamine per mg of rickettsial protein per hr at 37 C, while consuming 1.5 to 1.7 µmoles of O₂. R. quintana also utilized, in descending order, succinate, -ketoglutarate, glutamate, pyruvate, and citrate; the first-named substrate was utilized more rapidly than glutamine. R. quintana, like typhus rickettsiae, has a glutamate-oxaloacetate transaminase because aspartate was isolated, by means of thin-layer chromatography, as one of the end products of the utilization of glutamine. When the microorganisms were incubated with glutamine-¹⁴C and unlabeled intermediates of the citric acid cycle, labeled dicarboxylic acids of the cycle were recovered. Labeled tricarboxylic acids, however, were not recovered, possibly because of cellular impermeability to the corresponding unlabeled intermediates. In the case of cis-aconitate, it was shown that this substrate interfered with the uptake of glutamine. These observations are believed to provide convincing evidence that glutamine is utilized through the citric acid cycle and that R. quintana, with the differences noted, resembles other rickettsiae.

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