A strain of E. coli that produces a glycerol kinase insensitive to feedback inhibition by FDP is killed by the addition of glycerol. The product responsible for this effect diffuses to the medium and can be separated from the cells that produce it. Some characteristics of this product are: it has bactericidal effect on gram+ and gram- strains; it is produced by Hfr or F+ but not by F- strains; it inhibits protein synthesis; it is dialyzable and heat stable.