Vector competence of Culicoides bolitinos and C. imicola for South African bluetongue virus serotypes 1, 3 and 4

Abstract .The susceptibility of field-collected Culicoides bolitinos to infection by oral ingestion of bluetongue virus serotypes 1, 3 and 4 (BLU 1, 3 and 4) was compared with that of field-collected C. imicola and laboratory reared C. variipennis sonorensis . The concentration of the virus per millilitre of bloodmeal was 10^5.0 and 10^6.0TCID₅₀ for BLU 4 and 10^7.2TCID₅₀ for BLU 1 and 3. Of 4927 C. bolitinos and 9585 C. imicola fed, 386 and 287 individual midges survived 10 days extrinsic incubation, respectively. Midges were assayed for the presence of virus using a microtitration assay on BHK-21 cells and/or an antigen capture ELISA. Infection prevalences for the different serotypes as determined by virus isolation ranged from 22.7 to 82.0% in C. bolitinos and from 1.9 to 9.8% in C. imicola; infection prevalences were highest for BLU 1, and lowest for BLU 4 in both species. The mean log₁₀ TCID₅₀ titre of the three BLU viruses per single fly was higher in C. bolitinos than in C. imicola . The results suggested that C. bolitinos populations are capable vectors of the BLU viruses in South Africa. A high correlation was found between virus isolation and ELISA results for the detection of BLU 1, and less for BLU 4; the ELISA failed to detect the presence of BLU 3 in infected flies. The C. v. sonorensis colonies had a significantly lower susceptibility to infection with BLU 1, 3 and 4 than C. bolitinos and C. imicola . However, since infection prevalence of C. v. sonorensis was determined only by ELISA, this finding may merely reflect the insensitivity of this assay at low virus titres, compared to virus isolation.     

Symbiotic and competitive properties of motility mutants of Rhizobium trifolii TA1

Non-motile mutants of Rhizobium trifolii defective in either flagellar synthesis or function were isolated by transposon Tn5 mutagenesis. they were indistinguishable from motile control strains in growth in both laboratory media and in the rhizosphere of clover roots. When each non-motile mutant was grown together with a motile strain in continuous culture, the numbers of motile and non-motile organisms remained in constant proportion, implying that their growth rates were essentially identical. When inoculated separately onto clover roots, the mutants and wildtype did not differ significantly in the number of nodules produced or in nitrogen fixing activity. However, when mixtures of equal numbers of mutant and wild-type cells were inoculated onto clover roots, the motile strain formed approximately five times more nodules than the flagellate or non-flagellate, non-motile mutants, suggesting that motility is a factor in competition for nodule formation.     

Oxidation of Ferrous Iron and Elemental Sulfur by Thiobacillus ferrooxidans

The oxidation of ferrous iron and elemental sulfur by Thiobacillus ferrooxidans that was absorbed and unabsorbed onto the surface of sulfur prills was studied. Unadsorbed sulfur-grown cells oxidized ferrous iron at a rate that was 3 to 7 times slower than that of ferrous iron-grown cells, but sulfur-grown cells were able to reach the oxidation rate of the ferrous iron-adapted cells after only 1.5 generations in a medium containing ferrous iron. Bacteria that were adsorbed to sulfur prills oxidized ferrous iron at a rate similar to that of unadsorbed sulfur-grown bacteria. They also showed the enhancement of ferrous iron oxidation activity in the presence of ferrous iron, even though sulfur continued to be available to the bacteria in this case. An increase in the level of rusticyanin together with the enhancement of the ferrous iron oxidation rate were observed in both sulfur-adsorbed and unadsorbed cells. On the other hand, sulfur oxidation by the adsorbed bacteria was not affected by the presence of ferrous iron in the medium. When bacteria that were adsorbed to sulfur prills were grown at a higher pH (ca. 2.5) in the presence of ferrous iron, they rapidly lost both ferrous iron and sulfur oxidation capacities and became inactive, apparently because of the deposition of a jarosite-like precipitate onto the surface to which they were attached.     

Evolution and expression of the transplantation antigen gene family

We have cloned 26 different class I genes that are located in the major histocompatibility complex of the C57BL/10 mouse. Two of the three class I genes found in the H-2 complex encode the H-2Kb and H-2Db antigens; the other 23 class I genes map to the adjacent Tla complex. We have grouped the cosmids containing these genes into three clusters: one cluster links the H-2K and I-A regions, one cluster links the H-2D and Qa-2 regions, and the final cluster maps to the TL region. The class I gene organizations in the Qa-2 and TL regions of the C57BL/10 and BALB/c mice are generally similar, but there are several polymorphic segments. The Qa-2 region of both mice seems to have evolved by the duplication of gene pairs; furthermore, the H-2K region may have been generated by the translocation of a gene pair from the Qa-2 region. We have evidence that several of the genes in the Qa-2 region are expressed.     

Variants within the yeast Ty sequence family encode a class of structurally conserved proteins.

The Ty transposable elements of Saccharomyces cerevisiae form a heterogeneous family within which two broad structural classes (I and II) exist. The two classes differ by two large substitutions and many restriction sites. We show that, like class I elements a class II element, Tyl-17, also appears to contain at least two major protein coding regions, designated TYA and TYB, and the organisational relationship of these regions has been conserved. The TYA genes of both classes encode proteins, designated p1 proteins, with an approximate molecular weight of 50 Kd and, despite considerable variation between the TYA regions at the DNA level, the structures of these proteins are remarkably similar. These observations strongly suggest that the p1 proteins of Ty elements are functionally significant and that they have been subject to selection.     

Immunomodulation by Histoplasma capsulatum products; polyclonal activation and mitogenic effects

The presence of reactive spleen cells to sheep red blood cells (SRBC) in nonimmunized BALB/c mice injected with histoplasmin, the culture filtrate of Histoplasma capsulatum, was monitored for 21 days following inoculation. Polyclonal activation, as evidenced by a sharp increase in the number of anti-SRBC rosetteforming cells (RFC), as well as an enhanced response to heterologous non-cross-reactive erythrocytes from other species, was found in the spleens of these rodents on Days 11 to 13. Elimination of B-cell-derived RFC by the addition of complement indicated that the erythrocyte-binding cells consisted of both T- and B-lymphocytes. An immunosuppressive effect was detected if histoplasmin was injected 2 days before the antigen (SRBC), but could be reversed by injecting the filtrate 30 min prior to the antigen, as is found with polyclonal activators displaying immunosuppressive activity. Histoplasmin also had a mitogenic effect on lymphocyte obtained from the spleen, bone marrow, and thymus similar in magnitude to that produced by lipopolysaccharide (LPS) and concanaval in A. The biological significance of these findings is discussed.     

Influence of pipecolic acid on the release and uptake of [3H]GABA from brain slices of mouse cerebral cortex

Recently, pipecolic acid (PA) has been involved in the functioning of the GABAergic system. In the present work we have studied the effect of PA on GABA uptake and release in cerebral cortex slices. PA (100 M) was able to increase the release of [³H]GABA (90%) stimulated by mild depolarization with 15 mM potassium. If during the labeling of the tissue with [³H]GABA, -alanine was present, PA also enhanced the release (42%). However, when nipecotic acid was present instead -alanine, no stimulation of [³H]GABA release by potassium was observed neither in the control nor in the presence of PA. Spontaneous release was not affected by PA in any of the experimental conditions tested. In uptake experiments, only when -alanine was present in the medium PA significantly diminished the uptake (36%) of [³H]GABA. These results suggest that the effect of PA is mostly at the presynaptic level, inhibiting the neuronal GABA uptake and/or enhancing its release.