streaking to check phage sensitivity was done using a P22 clear-plaque mutant, H5. Electroporation of low ionic strength cell suspensions was done with a Gene Pulser (BioRad; Hercules, CA) as specified by the manufacturer and used at the following settings: capacitance, 25 [F; capacitance extender, 250 [F; pulse controller 200 Q; voltage, 2.5kV using cuvettes with a 0.2 cm gap. Putative transformants were purified by single colony isolation. Plasmid DNA was isolated with Qiagen Spin mini-prep kits (Qiagen Inc., Santa Clarita, CA).

Cloning of thepduB Gene for Complementation Studies

     Vectorplac22 was used for cloning the pduB gene so that its expression could be induced by IPTG (Bobik et al. 1997). The DNA used for cloning was obtained via PCR amplification of plasmid, pVJ70, using the following primers: forward 5'GGAATTCAGATCTATGGCAGAAAAAAGCTGCAGTTTAACG-3'; and reverse, 5'AAGGATCCAAGCTTTGAATCAGCCTCGTGGGTATCAGATG-3'. The BglII (forward primer) and HindIII (reverse primer) sites are underlined. Pfu polymerase was employed for the amplification because of its high fidelity of replication. The amplified DNA was gel purified and ligated to plac22 that had been digested with the same restriction enzymes and gel purified. The ligation was heated to 700C for 15 minutes to inactivate the ligase and then used to transform S. enterica TR6579 by electroporation. A clone (pGH9) containing an insert of expected size (722 bp) was moved into BE38 by transduction to create strain GH42.

Complementation Studies

     Strains were grown in batch culture at 370C, with shaking at 275 RPM, in 125 or 250 ml Erlenmeyer flasks. NCE minimal medium supplemented with either 1%