Evaluation of the chitin-binding dye Congo red as a selection agent for the isolation, classification, and enumeration o
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Evaluation of the chitin-binding dye Congo red as a selection agent for the isolation, classification, and enumeration of ascomycete yeasts Tomas Linder1 Received: 3 February 2018 / Revised: 19 February 2018 / Accepted: 21 February 2018 © The Author(s) 2018. This article is an open access publication
Abstract Thirty-nine strains of ascomycete yeasts representing 35 species and 33 genera were tested for their ability to grow on solid agar medium containing increasing concentrations of the chitin-binding dye Congo red. Six strains were classified as hypersensitive (weak or no growth at 10 mg/l Congo red), five were moderately sensitive (weak or no growth at 50 mg/l), three were moderately tolerant (weak or no growth at 100 mg/l), while the remaining 25 strains were classified as resistant (robust growth at ≥ 100 mg/l) with 20 of these strains classified as hyper-resistant (robust growth at 200 mg/l). Congo red growth phenotypes were consistent within some families but not others. The frequency of Congo red resistance among ascomycete yeasts was deemed too high for the practical use of Congo red as a selection agent for targeted isolation, but can be useful for identification and enumeration of yeasts. Keywords Antifungal · Cell wall · Phenotype · Yeast
Introduction The development of genome sequencing over the past four decades has revolutionized yeast taxonomy and now enables nearly unambiguous species identification (Hittinger et al. 2015). More recent developments in spectroscopic methods also allows for rapid and direct identification of yeast isolates (Quintilla et al. 2017). Before the advent of these technologies, yeast species were exclusively identified using morphological and physiological characterization (Kurtzman et al. 2011). However, these methods are still widely used in many parts of the world, where sequencing or spectroscopic facilities are not readily available. Physiological properties of yeasts can also be used for targeted isolation of particular taxonomic groups. Chemically defined cultivation media that contain either selective growth inhibitors or selected carbon and/or nitrogen sources can be used for targeted isolation of certain taxonomic Communicated by Erko Stackebrandt. * Tomas Linder [email protected] 1
Department of Molecular Sciences, Swedish University of Agricultural Sciences, Box 7015, 750 07 Uppsala, Sweden
groups of yeasts. For example, chemically defined growth medium containing methanol as the sole carbon source is commonly used to isolate species of methylotrophic yeasts (van Dijken and Harder 1974). A third use of physiological properties of yeasts is the enumeration of viable yeast cells in mixed cultures using colony counting assays, which requires the use of selective media to distinguish individual yeast strains and species from each other. The anionic azo dye Congo red (disodium benzidinediazo-bis-1-napthylamine-4-sulfonate) was originally developed for the textile industry (Steensma 2001) and is used routinely to stain chitin in microsc
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