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Urease testing and yeast taxonomy.

J L Booth, H S Vishniac

    Canadian Journal of Microbiology
    |May 1, 1987
    PubMed
    Summary
    This summary is machine-generated.

    Basidiomycetous yeasts, including the Cryptococcus vishniacii complex, produce urease, contrary to previous reports. Conventional urease testing can yield anomalous results due to medium acidification and alkalinization.

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    Area of Science:

    • Microbiology
    • Yeast Taxonomy
    • Enzymology

    Background:

    • Urease activity in yeasts is a key characteristic for identification and understanding metabolic pathways.
    • Previous studies indicated certain yeast groups, like the Cryptococcus vishniacii complex, were urease-negative.
    • Conventional urease testing methods can be prone to inaccuracies.

    Purpose of the Study:

    • To re-evaluate urease production in various yeast species using [14C]urea hydrolysis.
    • To investigate the causes of anomalous results in conventional urease testing, specifically Roberts' rapid urea hydrolysis (RUH) test.
    • To assess the impact of ethylenediaminetetraacetic acid (EDTA) on urease production and its potential for differentiating yeast varieties.

    Main Methods:

    • Assaying urease production via [14C]urea hydrolysis to measure 14CO2 production.

    Related Experiment Videos

  • Utilizing Roberts' rapid urea hydrolysis (RUH) test and comparing results with [14C]urea hydrolysis.
  • Culturing yeasts in media with and without ethylenediaminetetraacetic acid (EDTA) to observe effects on urease production.
  • Supplementing EDTA-containing media with Ni+2 to investigate restoration of urease activity.

    • Main Results:

    • All tested basidiomycetous yeasts, including the Cryptococcus vishniacii complex, demonstrated significant urease activity.
    • The Schizosaccharomycetaceae were the sole urease-positive ascomycetous yeasts identified; Yarrowia lipolytica was urease-negative.
    • Anomalous RUH test results were attributed to medium pH changes from endogenous metabolism and autolysis, and also to prior growth in the presence of EDTA.
    • Ethylenediaminetetraacetic acid (EDTA) inhibited urease production in most yeasts, except Filobasidiella (Cr.) neoformans var. neoformans.
    • The RUH test differentiated between Filobasidiella neoformans varieties based on EDTA resistance, with var. neoformans being more resistant than var. bacillispora.
    • Urease production in Fil. neoformans var. bacillispora was restored by Ni+2 in the presence of EDTA.

    Conclusions:

    • Basidiomycetous yeasts are generally urease-positive, necessitating a revision of previous classifications.
    • Conventional urease tests require careful interpretation due to potential interference from metabolic byproducts and chelating agents like EDTA.
    • Ethylenediaminetetraacetic acid (EDTA) sensitivity and Ni+2 supplementation can serve as valuable tools for differentiating yeast varieties within the Filobasidiella genus.