Characterization of an autostimulatory substance produced by Escherichia coli

The recovery of dilute populations of stationary phase cells of Escherichia coli was studied using an automatic growth analyser. The addition of 30% s upernatant from 2-d-old stationary phase cells of the organism reproducibly shortened the apparent lag times by 22-57.5%, depending on the age of the inoculum. True lag times, as determined by colony counts, of stationary pha se cells were reduced by supernatant addition by 41-62%. The growth-stimula ting substance was characterized and partly purified from supernatants: the active material was shown to be dialysable, heat-stable, acid- and alkali- stable and protease-resistant. Extraction with ethyl acetate or ion-exchang e resins was not successful, but the active material could be quantitativel y extracted with ethanol after saturation with salt. It is concluded that t he active substance is a small, non-proteinaceous, non-ionic organic molecu le. Separation of extracts by HPLC indicated that the stimulatory substance is weakly hydrophobic and has retention times similar to those of uracil. So far, however, the exact chemical identity of the active substance has no t been elucidated.