Ultrastructure of the Surface of Rickettsia prowazeki and Rickettsia akari

Negative-contrast electron microscopy revealed that the outer layer of the envelope of rickettsiae is composed of a matrix of tetragonally arranged subunits. The layer projects approximately 7 nm from the cell wall. It is suggested that this outer layer is analogous to the structure considered capsule-like in morphology.     

Experimental infection of domestic animals with R. prowazeki and R. canada]

The authors infected lambs with R. prowazeki and R. canada to ascertain their possible role in the natural infection of the animals. The lambs were infected subcutaneously with increasing doses; rickettsiemia was recorded with the aid of tests on guinea pigs and Ixodidae and Argasidae ticks fed on the lambs. Dynamics of antibody formation was ascertained in the infected animals in the agglutination reaction and in the complement fixation test. The antigenic affinity of R. canada and rickettsia of the typhoid group and the presence of common antigenic determinants with the Proteus OX19 was confirmed. The absence of any clinical manifestations, the character of antibody formation, impossibility of inducing the generalized infection and of the isolation of the causative agent from the blood pointed to the low susceptibility of lambs to R. prowazeki and R. canada; thus a possibility of circulation of the causative agents of typhius among the domestic animals scarcely probable.     

Characterization of a lysine-specific active transport system in Rickettsia prowazeki.

Rickettsia prowazeki possesses an active transport system for lysine with a Kt of influx of 1 muM. Extraction and chromatographic analysis of the accumulated labeled material show the material to be lysine rather than a derivative. This intracellular lysine pool can be exchanged with external unlabeled substrates for at least 10 min; The lysine analogues L-aminoethyl cysteine, N-methyl lysine, hydroxylysine, and D-lysine competitively inhibit uptake of L-lysine, but cadaverine, diaminopimelate, arginine, ornithine, and epsilon-aminocaproate do not. Accumulation of lysine can be inhibited by the energy poisons potassium cyanide, triphenylmethyl phosphonium bromide, and 2,4-dinitrophenol. The effect of potassium cyanide, but not 2,4-dinitrophenol or triphenylmethyl phosphonium bromide, can be overcome by adenosine 5'-triphosphate. Both energy-dependent influx and energy-independent efflux are inhibited by the sulfhydryl reagents N-ethyl maleimide and p-chloromercuriphenyl sulfonic acid.     

Electron Microscopy of the Cell Wall of Rickettsia prowazeki

Purified Rickettsia prowazeki were found to undergo morphological changes resembling plasmolysis when stained with uranyl acetate, resulting in rod-like forms. Sequential electron micrographs of disintegrating organisms provide evidence for the cell wall origin of these rod-like forms. The substructure of the cell wall was discerned by using negative-contrast electron microscopy. The wall was found to be composed of repetitive subunits with a periodicity of 13 nm and was surrounded by a thin membrane.     

Role of Erythrocytes and Serum in the Nutrition of Rickettsia quintana

Rickettsia quintana grew readily on blood-agar base when the following conditions and supplements were supplied: (i) aerobic conditions; (ii) increased CO(2) tension; (iii) crystalline hemoglobin or hemin, but not protoporphyrin; and (iv) a colloidal "detoxifying agent," such as starch or charcoal. Serum was not required nor did it enhance growth when all of the aforementioned components were supplied.     

Absence of hydrogen peroxide production by or catalase action in Rickettsia prowazeki.

Glutamic acid oxidation by Rickettsia prowazeki is not accompanied by hydrogen peroxide generation, nor is added hydrogen peroxide degraded, as measured by a manometric technique.     

Separation of inner and outer membranes of Rickettsia prowazeki and characterization of their polypeptide compositions.

Rickettsia prowazeki were disrupted in a French pressure cell and fractionated into soluble (cytoplasm) and envelope fractions. The envelope contained 25% of the cell protein, with the cytoplasm containing 75%. Upon density gradient centrifugation, the envelope fraction separated into a heavy band (1.23 g/cm3) and a lighter band (1.19 g/cm3). The heavy band had a high content of 2-keto-3-deoxyoctulosonic acid, a marker for bacterial lipopolysaccharide, but had no succinic dehydrogenase, a marker for cytoplasmic membrane activity, and therefore represented outer membrane. The lighter band exhibited a high succinate dehydrogenase activity, and thus contained inner (cytoplasmic) membrane. Outer membrane purified by this method was less than 5% contaiminated by cytoplasmic membrane; however, inner membrane from the gradient was as much as 30% contaminated by outer membrane. The protein composition of each cellular fraction was characterized by sodium dodecyl sulfate--polyacrylamide gel electrophoresis. The outer membrane contained four major proteins, which were also major proteins of the whole cell. The cytoplasmic membrane and soluble cytoplasm exhibited a more complex pattern on gels.     

Nutritional Studies of Rickettsia quintana: Nature of the Hematin Requirement

Rickettsia quintana grew in a liquid medium consisting of a brain-heart infusion base supplemented with starch and hematin. The growth requirement for hematin could not be substituted by compounds of known catalytic activity for H(2)O(2), viz., catalase, potassium pyruvate, or charcoal, or by the reducing compounds sodium sulfite and sodium thioglycollate. R. quintana was catalase-negative, but no H(2)O(2) production could be demonstrated by the catalase-aminotriazole technique. A minimum inoculum giving 10(5) cells/ml was required to initiate growth. The generation time at 33 C was 10 hr. The temperature range for growth was 28 to 37 C. Growth was enhanced when succinate or glutamate was added as energy source.