No abstract

Starvation ofFurthermore, evidence suggests that the σ E and σ S regulons function through separate mechanisms in the SSR. In contrast, C-starvation does not appear to generate signals required for Cpx regulon induction which support the findings that it is not required for LT-CSS or cross-resistance to H 2 O 2 , pH 31 or PmB challenges. However, it was required to achieve maximal cross-resistance to 55 SC. Therefore, σ E is a key regulatory component of the SSR and represents an additional σ factor required for the SSR of Salmonella.

The Epstein-Barr virus (EBV) gH-gL complex includes a third glycoprotein, gp42. gp42 binds to HLA class II on the surfaces of B lymphocytes, and this interaction is essential for infection of the B cell. We report here that, in contrast, gp42 is dispensable for infection of epithelial cell line SVKCR2. A soluble form of gp42, gp42.Fc, can, however, inhibit infection of both cell types. Soluble gp42 can interact with EBV gH and gL and can rescue the ability of virus lacking gp42 to transform B cells, suggesting that a gH-gL-gp42.Fc complex can be formed by extrinsic addition of the soluble protein. Truncated forms of gp42.Fc that retain the ability to bind HLA class II but that cannot interact with gH and gL still inhibit B-cell infection by wild-type virus but cannot inhibit infection of SVKCR2 cells or rescue the ability of recombinant gp42-negative virus to transform B cells. An analysis of wild-type virions indicates the presence of more gH and gL than gp42. To explain these results, we describe a model in which wild-type EBV virions are proposed to contain two types of gH-gL complexes, one that includes gp42 and one that does not. We further propose that these two forms of the complex have mutually exclusive abilities to mediate the infection of B cells and epithelial cells. Conversion of one to the other concurrently alters the ability of virus to infect each cell type. The model also suggests that epithelial cells may express a molecule that serves the same cofactor function for this cell type as HLA class II does for B cells and that the gH-gL complex interacts directly with this putative epithelial cofactor.

The genus Cellulomonas is comprised of a group of Gram-positive, soil bacteria capable of utilizing cellulose as their sole source of carbon and energy. Cellulomonas flavigena KU was originally isolated from leaf litter and subsequently shown to produce large quantities of a curdlan-type (beta-1,3-glucan) exopolysaccharide (EPS) when provided with an excess of glucose or other soluble carbon-source. We report here that curdlan EPS is also produced by Cellulomonas flavigena KU when growing on microcrystalline cellulose in mineral salts-yeast extract media. Microscopic examination of such cultures shows an adherent biofilm matrix composed of cells, curdlan EPS, and numerous surface structures resembling cellulosome complexes. Those Cellulomonas species that produce curdlan EPS are all non-motile and adhere to cellulose as it is broken down into soluble sugars. These observations suggest two very different approaches towards the complex process of cellulose degradation within the genus Cellulomonas.

FkpA is a peptidylprolyl isomerase whose expression is regulated by the alternative sigma factor, sigma factor E ( E ). In contrast to the results of a previous report, inactivation of fkpA was found to have only a minor effect on the ability of Salmonella enterica serovar Typhimurium to invade and survive within epithelial and macrophage cell lines and cause infection in mice. However, an effect of the fkpA mutation on serovar Typhimurium virulence was seen if the mutation was combined with mutations in surA or htrA, two other E -regulated genes, which encode proteins involved in protein folding and/or degradation in the periplasm.