Physiological characterization of osmotolerant yeast Pichia sorbitophila and comparison with a putative synonym Pichia farinosa.

The osmotolerant yeast Pichia sorbitophila was found to differ from other yeast species, not only from the conventional ones (Saccharomyces cerevisiae, Schizosaccharomyces pombe), but also from those widely known as osmotolerant (Debaryomyces hansenii, Zygosaccharomyces rouxii). P. sorbitophila was able to survive extremely high extracellular concentrations of salts (e.g., saturated solution of KCl) and other osmolytes (70% glucitol), although it is not classified as halophilic (or osmophilic). P. sorbitophila assimilated a broad range of carbon and nitrogen sources with extreme effectiveness. On solid media, P. sorbitophila created colonies of variable shapes and sizes in relation to media composition, number of colonies on the plate and cultivation conditions. Colonies were able to produce long-distance signals between each other that resulted in growth inhibition of the facing parts of both colonies, but were not inhibited by colonies of other yeast species growing on the same plate. Though sometimes P. sorbitophila has been indicated as a synonym of P. farinosa, comparative physiological studies together with PCR amplification of P. farinosa DNA fragments homologous to known P. sorbitophila genes provided a strong indication that this strain should be classified as a separate species.

Varicella-zoster Virus gB and gE coexpression, but not gB or gE alone, leads to abundant fusion and syncytium formation equivalent to those from gH and gL coexpression.

Varicella-zoster virus (VZV) is distinguished from herpes simplex virus type 1 (HSV-1) by the fact that cell-to-cell fusion and syncytium formation require only gH and gL within a transient-expression system. In the HSV system, four glycoproteins, namely, gH, gL, gB, and gD, are required to induce a similar fusogenic event. VZV lacks a gD homologous protein. In this report, the role of VZV gB as a fusogen was investigated and compared to the gH-gL complex. First of all, the VZV gH-gL experiment was repeated under a different set of conditions; namely, gH and gL were cloned into the same vaccinia virus (VV) genome. Surprisingly, the new expression system demonstrated that a recombinant VV-gH+gL construct was even more fusogenic than seen in the prior experiment with two individual expression plasmids containing gH and gL (K. M. Duus and C. Grose, J. Virol. 70:8961-8971, 1996). Recombinant VV expressing VZV gB by itself, however, effected the formation of only small syncytia. When VZV gE and gB genes were cloned into one recombinant VV genome and another fusion assay was performed, extensive syncytium formation was observed. The degree of fusion with VZV gE-gB coexpression was comparable to that observed with VZV gH-gL: in both cases, >80% of the cells in a monolayer were fused. Thus, these studies established that VZV gE-gB coexpression greatly enhanced the fusogenic properties of gB. Control experiments documented that the fusion assay required a balance between the fusogenic potential of the VZV glycoproteins and the fusion-inhibitory effect of the VV infection itself.

Effect of IFN-gamma receptor gene deletion on vaccinia virus virulence.

Two vaccina virus (VV) strains, WR and Praha, were selected for a study undertaken to determine whether the virus-encoded interferon-gamma receptor (IFN-gamma R) plays any role in virus virulence. Both of the viruses expressed the B8R gene coding for IFN-gamma R in infected cell cultures. The nucleotide sequence of the Praha virus B8R gene was determined, and, when compared with the published sequence of the WR virus, it only displayed one silent nucleotide substitution. Mutants of the WR and Praha viruses with deleted B8R gene were constructed. In rabbits, skin lesions produced by the WR B8R-deleted mutants were smaller and tended to disappear earlier than those caused by wild-type WR virus. Similar results were obtained with both independently prepared WR B8R-deleted mutants. These data strongly suggested that the product of B8R gene did play a role in virus virulence. A similar comparison of the wild-type Praha virus and its mutant could not be done because of the very low virulence of the parental virus for rabbits.

Immune response to vaccinia virus recombinants expressing glycoproteins gE, gB, gH, and gL of Varicella-zoster virus.

Immunogenicity of Varicella-zoster virus glycoproteins gE, gB, gH, and gL expressed by recombinant vaccinia viruses (VV) separately or simultaneously was determined in mice and guinea pigs by ELISA, Western blotting, radioimmunoprecipitation, plaque reduction assay, and skin test. Single VV-gE and VV-gB recombinants and double VV-gH/gL recombinant elicited specific antibodies with VZV neutralizing activity in mice. Co-expression of gE and gB by one recombinant VV resulted in an increased antibody response in comparison with immunization with single recombinants or their mixtures. Unlike anti-gB and anti-gH/gL antibodies, the gE-specific antibodies had no virus neutralizing activity in absence of complement, and when used alone, they even caused considerable increase of VZV infectious units. Moreover, immune sera containing anti-gE antibodies antagonized complement independent virus-neutralizing activity of anti-gB- and anti-gH/gL-positive sera. The ability to induce delayed hypersensitivity reaction to VZV antigens was observed after immunization of guinea pigs with gE- and/or gB-expressing VVs.

Characterization of interaction of gH and gL glycoproteins of varicella-zoster virus: their processing and trafficking.

Varicella-zoster virus (VZV) glycoproteins gH and gL were examined in a recombinant vaccinia virus system. Single expression of glycoprotein gL produced two molecular forms: an 18 kDa form and a 19 kDa form differing in size by one endoglycosidase H-sensitive N-linked oligosaccharide. Coexpression of gL and gH resulted in binding of the 18 kDa gL form with the mature form of gH, while the 19 kDa gL form remained uncomplexed. The glycosylation processing of gL was not dependent on gH; however, gL was required for the conversion of precursor gH (97 kDa) to mature gH (118 kDa). Subsequent analyses indicated that gL (18 kDa) was a more completely processed gL (19 kDa). Screening of the culture media revealed that gH and gL were secreted, but only if coexpressed and complexed together. The secreted form of gL was 18 kDa while that of gH was 114 kDa. The fact that secreted gH was smaller than intracytoplasmic gH suggested a proteolytic processing event prior to secretion. The 19 kDa form of gL was never secreted. These findings support a VZV gL recycling pathway between the endoplasmic reticulum and the cis-Golgi apparatus.

Induction of varicella-zoster virus-neutralizing antibodies in mice by co-infection with recombinant vaccinia viruses expressing the gH or gL gene.

Recombinant vaccinia viruses (VV) expressing the varicella-zoster virus (VZV) glycoprotein H (gH) or glycoprotein L (gL) were constructed. The 94 kDa gH intermediate glycoprotein was synthesized in cell cultures infected with the VV-gH recombinant, but only co-infection with both recombinants resulted in the synthesis of the fully processed 118 kDa gH molecule. The VV-expressed gH and gL formed a complex that displayed the conformational neutralization epitope detectable by means of human VZV gH-specific monoclonal antibody V3. Formation of this epitope was inhibited by tunicamycin but not by monensin. Simultaneous intraperitoneal inoculation of mice with high doses of both VV-gH and VV-gL viruses resulted in the development of VZV-neutralizing, complement-independent antibodies; these antibodies were not detected in mice infected solely with either the VV-gH or the VV-gL recombinant.