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Abstract
SUMMARY: Phormidium persicinum requires light intensities < 300 foot-candles and grows at 10°–33°. The medium developed for P. persicinum is representative of the early types of artificial media having a relatively high concentration of chelator and, necessarily, of trace metals. Other media, varying widely in trace metal: chelator ratios and concentrations allow growth of P. persicinum. Tris 2-amino-2- hydroxymethylpropane-1:3-diol is a suitable pH buffer; its antagonism of potassium utilization was demonstrated and was amply overcome by the addition of 200 mg. K/l. to the medium. Inorganic and organic phosphates were utilized and were required at relatively low concentrations. P. persicinum utilized NO3 − and NH4 + but not atmospheric nitrogen. NaNO3 was the most satisfactory inorganic nitrogen source but the cultures bleached after prolonged growth. Asparagine (0·2–0·8 g./l.) maintained the normal purple pigmentation over a longer period; it served as a non-toxic slowly-utilized reservoir of available N. Vitamin B12 is the only essential vitamin and is needed at a concentration (100 mμg./l.) which is higher than for most algae. All the cobalamins including factor B, but not methionine or deoxy- ribosides, can substitute for vitamin B12. The physiological and ecological resemblances of P. persicinum to red or violet blue-green algae growing in deep water are discussed.
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