Isolation of intracellular symbiotes by immune lysis of flagellate protozoa and characterization of their DNA

HIV-1 infection and HIV-1 Tat protein permit the survival and replication of a non-pathogenic trypanosomatid in macrophages through TGF-beta1 production

Monoxenic trypanosomatids, which usually are non-pathogenic in humans, have been detected in AIDS patients, but the mechanisms underlying the establishment of these protozoa in HIV-1-infected individuals are poorly understood. Here we addressed the role of HIV-1 and the HIV-1 Tat protein in the replication of the monoxenic trypanosomatid Blastocrithidia culicis in HIV-1-infected primary human macrophages. We found that HIV-1 and B. culicis replication augmented almost three times in co-infected macrophages, and that Tat antiserum significantly reduced the exacerbated protozoan growth. Exposure of B. culicis only infected macrophages to Tat protein also resulted in enhanced protozoan proliferation, reaching a twofold increase at 100 ng/mL. Electron microscopy analysis revealed that B. culicis and HIV-1 co-habit the same cells, and showed protozoan dividing forms inside macrophages. Protozoan replication diminished when B. culicis only infected macrophages were treated with Tat protein in the presence of anti-TGF-beta1 antibodies, suggesting a participation of this cytokine in the augmentation of protozoan multiplication. In fact, exogenous TGF-beta1 promoted the trypanosomatid replication in macrophages. Overall, our results suggest that HIV-1 infection deactivates the macrophage microbicidal activity, permitting the survival and multiplication of an otherwise non-pathogenic protozoan in these cells, a process partially mediated by Tat protein, via TGF-beta1 secretion.

Endosymbiosis in protozoa of the Trypanosomatidae family

A small number of trypanosomatids present bacterium endosymbionts in the cytoplasm, which divide synchronously with the host cell. Crithidia oncopleti, Crithidia deanei. Crithidia desouzai, Blastocrithidia culicis and Herpetomonas roitmani are the best characterized species. The endosymbiont is surrounded by two membranes separated from each other by an electron-lucent space. The presence of the endosymbiont led to the appearance of morphological changes which include the lack of the paraflagellar rod associated to the axoneme, the morphology of the kinetoplast and the association of the sub-pellicular microtubules with portions of the protozoan plasma membrane. Aposymbiotic strains could be obtained by antibiotic treatment, opening the possibility to make comparative analysis of endosymbiont-containing an endosymbiont-free populations of the same species. It is clear that metabolic cycles are established between the prokaryiont and the host cell. The results obtained show that endosymbiont-containing species of trypanosomatids constitute an excellent model to study basic processes on the endosymbiont-host cell relationship and the origin of new organelles.

Aspects of the relation between Cyanophora paradoxa (Korschikoff) and its endosymbiotic cyanelles Cyanocyta korschikoffiana (Hall & Claus) - I. Growth, ultrastructure, photosynthesis and the obligate nature of the association

Ultrastructural studies of the symbiotic relation between the apochlorotic cryptomonad Cyanophora paradoxa and the cyanobacterium Cyanocyta korschikoffiana have demonstrated that the endosymbiotic cyano­bacteria are within host cell vacuoles and possess a highly reduced prokaryotic cell wall which becomes particularly evident during binary fission. Division by the endosymbiotic cyanobacteria was found not to be in synchrony with division by the host cryptomonad. The cyano­bacteria divided most rapidly when the host population had reached its asymptote, such that, in cultures in extended stationary phase, it is possible to observe as many as eight cyanobacteria in one host cell. Nutritionally, C. paradoxa was found to be an obligate phototroph; its auxotropic capabilities are confined to acetate and cyanocobalamin. Analysis of the rate of photosynthesis by the intact association demon­strated that saturation occurred at the 140 μE cm -2 s -1 (where E is einstein), and at saturating light intensities, the rate of CO 2 fixation was 30 μmol CO 2 (mg chl a ) -1 h -1 . The best rate of CO 2 fixation obtained by the isolated cyanobacteria represented 12% of the rate found in the intact association. Two independent methods of analysis showed that at best, only 15% of the carbon fixed by the cyanobacteria was translocated to the host, mostly as glucose and probably sucrose. Studies with metabolic inhibitors directed against the prokaryotic cyanobacteria demonstrated the close interdependence of the host with the endosymbionts, in that disruption of the endosymbionts always resulted in death of the host. Our inability to grow the cyanobacteria away from the host, combined with the apparent inability of the host to survive in the absence of the photosynthetic endosymbiotic cyanobacteria provide strong support for the concept that the association represents a well integrated mutually obligate relation, but the concept that the cyanobacteria are chloroplasts cannot be supported.

16S ribosomal DNA sequence identities of beta-proteobacterial endosymbionts in three Crithidia species

The 16S ribosomal DNA sequences of endosymbionts from the trypanosomatid protozoa (Crithidia spp.) are most homologous to that of Bordetella spp. This finding extends the polyphyletic origin of endosymbionts for the first time to the beta Proteobacteria. Biased base transitions and compensatory mutations of the symbionts' sequences that may contribute to their identity in the three Crithidia spp. are noted.

Symbiote-free hemoflagellates, Blastocrithidia culicis and Crithidia oncopelti: their liver factor requirement and serologic identity

Several aposymbiotic strains of Blastocrithidia culicis and Crithidia oncopelti were cultivated in Trager's chemically defined medium as well as in a blood broth, both supplemented with 0.25% (v/v) liver extract concentrate. For all such strains, the liver extract was found to serve as an essential growth factor in the defined medium and as growth promoting additive in the blood broth. The active molecules were found to be water-soluble, heat stable, dialyzable, and probably nonlipid fractions. Antisera were developed in rabbit against all the available aposymbiotic strains. An almost total cross-reactivity at very high titers was observed in reciprocal agglutination test using strains with and without the bacterial symbiotes. These results indicate that the loss of the symbiotes does not affect the antigenic identity of B. culicis and C. oncopelti.

Surface membrane carbohydrate alterations of a flagellated protozoan mediated by bacterial endosymbiotes

Crithidia oncopelti, a parasitic trypanosomatid protozoan of insects, normally contains intracellular symbiotic bacteria. As shown earlier, the protozoa can be rid of their endosymbiotes by chloramphenicol, producing a symbiote-free cell line. Here surface-membrane carbohydrate ligands of the symbiote-containing and symbiote-free strains were compared by lectin-mediated agglutination, lectin-ultrastructure localization. [3H] lectin-binding, and fluorescent lectin staining. Symbiote-free organisms consistently had 3-fold higher agglutination titers than symbiote-containing cells with concanavalin A. Conversely, symbiote-containing flagellates had 2- to 3-fold greater agglutination titers with a fucose-binding lectin than symbiote-free organisms. Ultrastructure results showed that more of concanavalin A-horseradish peroxidase-diaminobenzidine reaction product was present at the surface of symbiote-free than on symbiote-containing cells. Treatment with [3H]concanavalin A revealed that surface membrane sites available per cell for [3H]lectin-binding ranged from 6.2 to 7.4 x 10(4) and from 24 to 27 x 10(4) for symbiote-containing and symbiote-free organisms, respectively, i.e., the mean binding level of the latter for the lectin was 3.5 times greater than that of the former. Moreover, symbiote-free cells fluoresced more than symbiote-containing organisms after staining with fluorescein-labeled concanavalin A. Apparently, the prokaryotic endosymbiotes somehow alter the quantity of saccharide ligands in the C. oncopelti surface membrane.

Heme biosynthesis in bacterium-protozoon symbioses: enzymic defects in host hemoflagellates and complemental role of their intracellular symbiotes

Heme biosynthetic activity in the symbiotic association involving crithidial flagellates and intracellular bacteroids was studied by enzymic, nutritional, and isotope incorporation experiments. Component organisms and their complexes in this association were analyzed separately to determine the underlying cause of the hemin requirement of hemoflagellates and the role of symbiotes in sparing this requirement of two crithidial species. Nutritional study of symbiote-free flagellates showed that their growth requires at least 0.1 mug/ml of hemin, which can be substituted by protoporphyrin IX, but not by the porphyrin precursors, delta-amino-levulinic acid or porphobilinogen. These flagellates, in the presence of protoporphyrin IX, incorporated 59Fe into heme, indicating that they possess ferrochelatase (EC 4.99.1.1), the terminal enzyme in the heme biosynthetic pathway, which catalyzes the insertion of iron into protoporphyrin IX. In symbiote-containing flagellates serially cultured in a defined medium free of tetrapyrrole compounds, heme and porphyrins can be detected by a fluorophotometric method, indicative of heme biosynthesis. Study of [14C]glycine incorporation into heme showed that the rate is much higher in symbiote-containing flagellates than in those without symbiotes. Microassay of uroporphyrinogen I synthase [EC 4.3.1.8; porphobilinogen ammonia-lyase (polymerizing)] revealed that the specific activity is high in symbiote-containing flagellates and higher still in isolated symbiotes, but essentially negligible in symbiote-free organisms. It is concluded that the bacterial symbiotes augment a very limited heme biosynthetic capacity of host flagellates by supplying uroporphyrinogen I synthase and perhaps other enzymes preceding ferrochelatase in the heme biosynthetic chain.