phage transduction, expression plasmids, and an allele replacement system that uses linear transformation (Datsenko and Wanner 2000). In this dissertation studies of AdoB12-dependent PD degradation by S. enterica are used to improve our general understanding of B12.

                   B12-Dependent PD Degradation in S. enterica Degradation of Propanediol

1,2-propanediol

      Enteric bacteria encounter PD frequently, as it is a fermentation product of the

methylpentoses, rhamnose and fucose, which are prevalent in the soil and in the intestinal environment (Lin 1987, Obradors et al. 1988). In addition, fucose is a component of glycoconjugates found on the surface of intestinal epithelial cells where they participate in host-parasite interactions (Bry et al. 1996). In vivo expression technology (IVET) has suggested thatpdu genes are 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). The catabolism of PD in salmonella occurs in an Ado-B12dependent fashion and the genes required for this process map at the PD utilization (pdu) operon (Jeter 1990) (Figure 1-3).

The pdu locus

      Thepdu locus is situated adjacent to the cob operon and is comprised of thepduF and pocR genes which encode a PD diffusion facilitator and a transcriptional regulator, respectively, and the divergently transcribed pdu operon (Figure 1-3) (Chen et al. 1994, Bobik et al. 1997). Previously, our laboratory established the DNA sequence of thepdu operon and showed that it included 21 putative genes (Bobik et al. 1999). The pduCDE genes have been shown to encode the large, medium, and small subunits of diol