Session 3, Abstract 18

A GENETIC ANALYSIS OF THE ROLES PLAYED BY BACTERIOPHAGE E15 PROTEINS GP21 AND GP22 IN CONVERTING THE O-POLYSACCHARIDE OF ​SALMONELLA ANATUM​ FROM AN ALPHA-GLYCOSIDICALLY LINKED FORM TO A BETA-GLYCOSIDICALLY LINKED FORM

Amelia Krouse* (Michael McConnell), Department of Biology, Point Loma Nazarene University, 3900 Lomaland Drive, San Diego, CA 92106

A distinguishing feature of all Gram negative bacteria is the presence of lipopolysaccharide (LPS) on the cell surface. LPS is a structurally complex molecule consisting of: 1) lipid A, which anchors the molecule in the outer membrane; 2) R-core, an oligosaccharide attached to the lipid A that contains unusual 7C and 8C sugars, as well as most of the charged groups of the LPS molecule; and 3) O-polysaccharide, a hydrophilic polymer generated from a 3-6 sugar repeat unit that is attached to the outer tip of the R-core and which projects outward into the cell’s aqueous environment. Lipid A (aka endotoxin) is considered the most dangerous part of LPS from a medical standpoint, but the O-polysaccharide is also of significance, in that it is the part of the LPS molecule with which the human immune system initially interacts during an infection by Gram-negative bacteria. Bacteriophage E15 is a virus known to alter O-polysaccharide structure upon infection of its Salmonella enterica, serovar Anatum host cell. Normally, the mannosyl-rhamnosyl-galactose repeat units of Salmonella anatum O-polysaccharide polymers are held together by alpha glycosidic bonds, but upon infection or lysogenization by E15, the alpha linkages are replaced by beta linkages. We have conducted a two-pronged, genetic approach to analyze the roles played by bacteriophage E15 proteins gp21 and gp22 in bringing about this change. Specifically, we have deleted E15 genes 21 and 22, both individually and in combination, from Salmonella anatum (E15) lysogenic strains and we have also introduced each gene individually via low copy number plasmids into non-transformed Salmonella anatum host cells. The phenotypes of these deletion mutants and transformants indicate that bacteriophage E15 proteins gp21 and gp22 cooperate together to convert the alpha-glycosidically linked, O-polysaccharide polymer of Salmonella anatum into a beta-glycosidically linked, O-polysaccharide polymer.

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