Phosphorus and the Growth of Euglena gracilis

SYNOPSIS. Growth of streptomycin‐bleached Euglena gracilis depends in part on the availability of phosphorus. Maximum cell density on a defined medium is reached at a phosphorus (supplied as inorganic phosphate) concentration of 4–5 μ/ml. At lower concentrations, the cells apparently deplete the medium of phosphorus. Inorganic phosphorus at > 1 mg/ml inhibits growth in terms of cell density per ml and generation time. Phosphorus‐limited cells survive for at least 6–7 days and are able to undergo mitosis following a lag period when returned to phosphorus‐containing medium. The majority of inorganic ³²P incorporated by these Euglena ends up in the hot trichloroacetic acid soluble fraction and in the ethanol‐ether soluble fraction.