SUMMARY: cells were maintained on yeast extract/neopeptone/glucose medium (YNG). Experimental medium was depleted of endogenous metal ions by repeated passage of YNG over a chelating ion-exchange resin. This treatment did not compromise the glucose or vitamin content but provided a basal medium to which essential salts could be added in defined concentrations. Accordingly it was possible to demonstrate growth requirements by this yeast species for K, Mg, Zn and Fe. Na would not replace K. Additions of 1.0 μ;M-Ca, NH+ and Na, or 0.1 μ;M-Ni, Sn, Al, Co or Cr to a minimal, reconstituted medium were without effect. Cu and Mn additions were not required for growth but, like Mg, Zn and Fe, they positively affected the biosynthesis of periplasmic acid phosphatase. Cells from iron-depleted medium had only 1 unit (g dry wt) of native acid phosphatase activity although this could be stimulated 10-fold by addition of FeCl to washed cell suspensions before enzyme assay. Additions of 10-60 μ;M-FeCl to untreated YNG medium progressively increased the concentration of acid phosphatase after 3 d of culture to an upper value of 75 units (g dry wt), and also increased the amount secreted into the growth medium. While unfortified YNG supported cells with only 28% of their acid phosphatase expressed (the bulk being subject to activation by Fe in the assay medium) the cells from YNG fortified with 60 μ;M-FeCl displayed fully activated acid phosphatase. Cells from Mg-depleted medium exhibited bizarre, elongated cell shapes and those from Zn-deficient medium appeared somewhat angular by light microscopy. Fe-deficient cells had apparently normal morphology.


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