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.     

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.     

The action of philanthotoxin-343 and photolabile analogues on locust (Schistocerca gregaria) muscle

The effects of philanthotoxin-343 (PhTX-343; tyrosyl-butanoyl-spermine) and photolabile analogues of this synthetic toxin on locust (Schistocerca gregaria) skeletal muscle have been investigated using whole muscle preparations (twitch contractions), single muscle fibres (excitatory postsynaptic currents (EPSCs)) and muscle membrane patches containing single quisqualate-sensitive glutamate receptors (qGluR). Analogues containing an azido group attached to either the butanoyl side-chain of PhTX-343 or as a substitute for the hydroxyl moiety of the tyrosyl residue were about 6 fold more potent antagonists than PhTX-343; those with an azido group located at the distal end of the toxin molecule were generally 2–3 fold less potent than PhTX-343. When these compounds were tested in subdued light, they were reversible antagonists of the muscle twitch, EPSC and qGluR. When a muscle was irradiated with U.V. during application of photolabile toxin combined with either neural stimulation of the muscle orl-glutamate application, antagonism of the twitch, EPSC and qGluR was complete and irreversible.     

Microsomal and cytosolic cytochrome P450 mediated benzo(a)pyrene hydroxylation in Pleurotus pulmonarius

Summary Microsomal and soluble fractions of Pleurotus pulmonarius exhibited a reduced carbon monoxide difference spectrum with P450 maxima at 448nm and 450–452nm respectively. Substrate induced Type I spectra were observed on addition of benzo(a)pyrene to both fractions. Benzo(a)pyrene hydroxylation was measured using the aryl hydrocarbon hydroxylase assay and was observed to be P450 dependent as indicated by carbon monoxide inhibition together with the substrate binding characteristics. The activity of the fractions were observed to give K_m of 200mM and 660mM and V_max of 1.25 nmol/min/nmol P450 and 0.57 nmol/min/nmol P450 for the microsomal and cytosolic fractions respectively.