The major goal of this project is to understand how Salmonella uses formate to colonize the chick intestine, and to develop detailed knowledge of the metabolites present in the intestine of the chick during chick development. This knowledge is a first step to identify mechanisms that we can use to inhibit Salmonella colonization of the chick intestine. This knowledge may allow us to develop rationally designed probiotics that interfere with Salmonella colonization in the chick intestine.Objective 1. Identify the Salmonella genes needed for formate oxidation in the chick. Delete, individually and in combination, the formate dehydrogenases (FDH-N, FDH-H, and FDH-O) in either Salmonella Typhimurium or Enteritidis (both if funds permit) and test the resulting mutants for their ability to colonize chicks.Identify the terminal electron acceptor used by Salmonella in the intestine of chicks by deleting cytochrome oxidases and terminal electron acceptor reductases individually and testing the ability of mutants lacking these genes to colonize chicks.Identify the electron acceptor used during formate oxidation by generating double mutants lacking formate dehydrogenases and terminal electron acceptor reductases and testing the resulting mutants in competitive infections with FDH single mutants.Link all genes and phenotypes using complementation in trans.Objective 2: Determine intestinal formate level and correlate with taxonomic shifts and formate metabolic pathways in the microbiota.Quantify formate in the intestine of chicks using GC/MS, in both uninfected and infected animals in the first three weeks post-hatch, a critical period when the intestinal microbiota develop.Correlate changes in formate level to changes in the bacterial taxa present in the intestine and the active transcription of metabolic genes metagenomic analysis.Objective 3: Test commensal E. coli "Nissle" strains unable to generate formate for their ability to reduce Salmonella colonization in chicks. Colonize chicks soon after hatching using the commensal E. coli "Nissle" (EcN) strain and an EcN mutant lacking the ability to produce formate.Test the ability of chicks colonized with Nissle, but unable to produce formate, to support Salmonella colonization.