Tn-seq yields many false positive results.

The forty genes with the lowest relative fitness in the second growth period of MMC Tn-seq experiment are listed. Each gene was deleted and the deletion mutants were tested for sensitivity to MMC using a spot titer assay and a range of MMC concentrations. Genes labeled as not sensitive had no difference in growth relative to the WT strain on MMC containing media, with the exception of ylbK, which resulted in a polar effect on ylbL (see S3 Fig).