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Studies on the Extracellular Starch Production by Species of Torulopsis

1951; Kansas Academy of Science; Volume: 54; Issue: 1 Linguagem: Inglês

10.2307/3626250

1938-5420

Lewis E. Goyette,

Yeasts and Rust Fungi Studies

by Species of Torulopsis LEWIS E. GOYETTE, University of Kansas, Lawrence It was reported by Aschner, Mager, and Leibowitz (1945) that the yeasts Torulopsis neoformans (Sanfelice) Red. and Torulopsis rotundata Red. produced extracellular starch under special growth conditions. These conditions were: a shift in the hydrogen-ion concentration during growth to below pH 5; active cell proliferation; and the addition of thiamine. Any available source of carbon or of nitrogen which favored this acidification was satisfactory for starch production (Mager and Aschner, 1946, 1947). Aschner, Mager, and Leibowitz (1945) studied the properties of the starch produced and concluded that it probably consisted of at least two different polysaccharides, one of which corresponded to the amylose fraction of the starch of green plants, the other being a pentosan. This pentosan is derived from the capsule of the fungus (Mager and Aschner, 1947). In further studies on the polysaccharides of capsulated yeasts Mager (1947) reported that this yeast starch is probably intermediate between alpha amylose and beta amylose, and possibly identical with the gamma amylose compound of corn starch as described by Kerr and Severson (1943). The cultural and morphological resemblance of T. neoformans to contaminating non-pathogenic yeasts is confusing. In attempting to find a reliable character as an aid in identification, Mager and Aschner (1946) reported that a strain of T. neoformans, isolated from a case of torulameningitis, produced extracellular starch. The amount of starch produced could easily be detected by flooding the culture with Lugol's iodine solution. They were able to secure positive results with sixteen other strains of T. neoformans. A large number of fungi belonging to other yeast genera were also tested but none exhibited starch production. Mager (1947) demonstrated the presence of phosphorylase in the cells of T. rotundata. He stated that the probability is that the enzymatic apparatus for starch production might be liberated by destruction of the cellular organization. This destruction sets free a starch-producing enzyme which acts as a phosphorylase. The question remains why this phenomenon of extracellular starch formation is limited to a group of non-fermenting capsulated yeasts. The most plausible theory was stated in the paper by Mager (1947): Starch is the precursor of the yeast capsule pentosan. Under normal conditions