Biological Studies on Capsulated Yeasts

Abstract

Using Bei-jerinck''s auxanographic agar plate method, with a KH2PO4, MgSO4, glucose and yeast-or meat extract, addition of Lugol''s soln. showed that the N-source is not the controlling factor for growth and starch production by the capsulated, non-fermenting yeast, Torulopsis rotundata. Nitrates caused growth but no starch formation. Inorganic ammonium salts caused both phenomena, the cations'' assimilation decreasing pH''s below 5, this decrease proving to be the governing factor for starch formation. Starch accumulated only extraplasmotically; the cells were abnormal, with detached or ruptured capsules. Thiamine is the only vitamin required. In an aerated (NH4)2SO4, KH2PO4, 0.5 to 0.8% glucose medium, maximal growth and starch yields occurred at pH 3 to 4. Active cell proliferation is essential to starch formation. Of 36 C-sources studied, only those affording growth and medium acidification served as starch-yielding substrates. Growth and extracellular starch were measured photometrically, starch in the medium by extinction values of the blue color with standard iodine solution, and pH''s colorimetri-cally. 28 starch-positive and 38 starch-negative spp. or strains were encountered, starch production being limited exclusively to capsulated, non-fermenting and non-sporulating yeasts, pathogenic and non-pathogenic. Alcohol precipitated a polysaccharide (85% pentose, 15% hexose) from media in which capsulated yeasts had grown, none when non-capsulated yeasts were cultured. T. rotundata displays an S-M variation; only the M-form is capsulated, producing the polysaccharide. The capsular material is devoid of immuno-logical activity.