CHAPTER 2
ANALYSES OF POLYHEDRAL ORGANELLE FORMATION IN Salmonella enterica SEROVAR TYPHIMURIUM LT2

                                   Introduction

     Virtually all salmonella degrade PD in a coenzyme B12-dependent fashion, and this ability (which is absent in E. coli) is thought to be an important aspect of the Salmonellaspecific lifestyle (Jeter 1990). PD is likely to be encountered by Salmonella in the host organism's gut, as it is a fermentation product of the plant sugars fucose and rhamnose (Lin 1987, Obradors et al. 1988). Additionally, fucose is a constituent of glycoconjugates found on intestinal epithelial cells, where it is involved in host-parasite interactions (Bry et al. 1996). In vivo expression technology (IVET) has indicated that the PD utilization (pdu) genes of S. enterica, may be important for growth in host tissues, and competitive index studies in mice have shown thatpdu mutations confer a virulence defect (Conner et al. 1998, Heithoff et al. 1999). Hence, the degradation of PD appears to play an important role in the interaction of Salmonella with its host organisms.

     The catabolism of PD has been investigated (Toraya et al. 1979, Obradors et al. 1988). The process is initiated by the conversion of PD to propionaldehyde, a reaction catalyzed by the B12-dependent diol dehydratase (Abeles and Lee Jr. 1961). The aldehyde is then disproportionated to propanol by a putative propanol dehydrogenase, and to propionic acid, presumably by a CoA-dependent propionaldehyde dehydrogenase, phosphotransacylase, and propionate kinase. This pathway provides a source of energy, an electron sink and a carbon source that can be channeled into central metabolism via