The Amino Acid Requirements of a Single Strain of Actinomyces israelii Growing in a Chemically Defined Medium

The Wills strain of Actiiiornyces israelii will survive repeated subculture in the medium HP 9 described by Christie & Porteous (1962 b) but modified to contain ammonium sulphate and only seven amino acids (serine, cysteine, glutamic acid, lysine, leucine, isoleucine and tryptophan) ; the total-N content of this new medium was 240 pg./ml. On the evidence available this new medium probably represents the minimal medium in respect of amino acids (and growth factors) for this strain of Acti?zomyces israelii. The yield of organism from this new medium was comparable with that reported by Christie & Porteous ( 1 9 6 2 ~ ) for more complex media, namely approximately 70 pg. cell total-N/ml. medium. Some observations are presented on inhibition of growth of Actinomyces israelii by ‘growth factors ’ and by purine and pyrimidine bases