Isolation and characterization of substance in yeast extract which inhibits growth of thymine-less strains of Escherichia coli

SUMMARY: Yeast extract which promotes the growth of wild-type strains of Escherichia coli had a potent bactericidal action on thymine-less mutants. The active principle in the yeast extract was found to be adenosine. All of the other nucleosides and their bases tested except guanine, hypoxanthine and inosine also showed various degrees of bactericidal activity. The activity of adenosine was competitively annulled by the addition of excess thymidine to the medium, but thymine showed practically no anti-adenosine effect.