In Salmonella Typhimurium YB1, the asd gene was placed under a hypoxia-inducible promoter so that in the hypoxic tumor microenvironment, the bacteria would survive, but in normal tissues, the asd gene would not be expressed and the bacteria would lyse.40 This strain also has an aroA deletion making it an aromatic compound auxotroph. This evidence concerns the gene ARSD and neoplasm.