| description |
An estimated 1.1 million transposon mutants in S. Typhi have been assayed using Illumina nucleotide sequencing from within the transposon into the adjacent target DNA. With this method, which we have called TraDIS (Transposon Directed Insertion-site Sequencing), we have been able to map 394,000 unique transposon insertion sites to the Salmonella enterica serovar Typhi chromosome. The unprecedented density and resolution of mapped insertion sites, an average of 1 every 15 bp, has allowed us to assay simultaneously every gene in the genome for essentiality and generate a genome-wide list of candidate essential genes. In addition, the semi-quantitative nature of the assay allowed us to identify genes that are advantageous and those that are disadvantageous for growth under standard laboratory conditions. Comparison of the mutant pool following growth in the presence or absence of ox bile enabled every gene to be assayed for its contribution towards bile tolerance, a trait required of any enteric bacterium and for carriage of S. Typhi in the gallbladder. This screen validated our hypothesis that we can simultaneously assay every gene in the genome to identify niche-specific essential genes. |