Cletus P. Kurtzman

Methods for isolation, phenotypic characterization and maintenance of yeasts

Yeasts are recovered from a wide range of aquatic, marine, atmospheric, and terrestrial habitats. Many yeasts occur widely, whereas some appear to be confined to specific habitats. Yeasts seldom occur in the absence of either molds or bacteria. Consequently, selective techniques are often used for recovery of yeasts, employing media that permit the yeasts to grow, while suppressing molds and bacteria. Under the morphological characterization of yeasts there are several factors that include: texture, color, surface, elevation, and margin. In texture, mucoid growth is frequently associated with encapsulation of cells from production of extracellular polysaccharides; membranous growth generally results from profuse formation of hyphae or pseudohyphae. In color, the presence of red, orange, or yellow nondiffusible carotenoid pigments is characteristic of certain genera, for instance, Phaffia, Rhodosporidium, and Sporidiobolus. In surface, the strains that are smooth when first isolated sometimes become rough when maintained on agar. This change is, in some cases, accompanied by a change in texture from butyrous to membranous. Restreaking generally results, once again, in formation of smooth and rough colonies. In elevation, the growth is flat, depressed in the center, raised and dome-like, or conical. And in margin, the edge of the streak or colony is entire, undulating, lobed, erose, or fringed with hyphae or pseudohyphae.

Chapter 90 – Candida Berkhout (1923)

Publisher Summary This chapter studies the genus Candida. In the asexual reproduction it is seen that cells are globose, ellipsoidal, cylindroidal, or elongate and occasionally ogival, triangular, or lunate. Reproduction is by holoblastic budding. Pseudohyphae and septate hyphae may be formed. The cell wall is ascomycetous and two-layered. Ballistoconidia are not formed. Arthroconidia may be formed, but not extensively. Sexual reproduction is absent. The chapter also discusses physiology/biochemistry and phylogenetic placement of the genus in which glucose may be fermented, nitrate may be assimilated, and starch-like compounds are not produced. The diazonium blue B reaction is negative and xylose, rhamnose, and fucose are not present in cell hydrolysates. The type species taken is Candida vulgaris. The chapter also explores the systematic discussion of the species that involves growth on YM agar, growth in glucose-yeast extract broth, and Dalmau plate culture on corn meal agar.

Sexual Reproduction in Candida lipolytica

Candida lipolytica is a rather common yeast isolated more frequently from substrates containing lipids or proteins, such as dairy products, than from substrates rich in sugars. This species assimilates hydrocarbons and is currently being studied for its potential to convert petroleum into yeast cells for use in feeds and foods. We have found C. lipolytica to exist in nature primarily in the heterothallic haploid state. When appropriate strains of opposite sex are mixed on a suitable sporulation medium, conjugation occurs followed by the production of ascospores. Since heterothallism permits laboratory control of hybridization, this characteristic of C. lipolytica enhances the possibility of im proving its strains for technological uses.

Structural characterization of novel sophorolipid biosurfactants from a newly identified species of Candida yeast

Sophorolipids are a group of O-acylsophorose-based biosurfactants produced by several yeasts of the Starmerella clade. The known sophorolipids are typically partially acetylated 2-O-β-D-glucopyranosyl-D-glucopyranose (sophorose) O-β-glycosidically linked to 17-L-hydroxy-Δ9-octadecenoic acid, where the acyl carboxyl group often forms a 4″-lactone to the terminal glucosyl residue. In a recent MALDI-TOFMS-based screen for sophorolipid-producing yeasts we identified a new species, Candida sp. NRRL Y-27208, that produces significant amounts of novel sophorolipids. This paper describes the structural characterization of these new compounds, using carbohydrate and lipid analysis, mass spectrometry, and NMR spectroscopy. Unlike those reported previously, the NRRL Y-27208 sophorolipids contain an ω-hydroxy-linked acyl group (typically 18-hydroxy-Δ9-octadecenoate), and occur predominantly in a non-lactone, anionic form. In addition, 17 dimeric and trimeric sophoroses were identified by MALDI-TOFMS from this strain. The surfactant-like properties of these sophorolipids have value as potential replacements for petroleum-based detergents and emulsifiers.

Gene Sequence Analyses and other DNA-Based Methods for Yeast Species Recognition

Publisher Summary This chapter focuses on the resolution of species using various types of DNA comparisons. DNA sequence analyses, and other DNA-based methodologies, have transformed the way in which yeasts are identified. DNA comparisons of yeasts have paralleled the increasing sophistication of methods for nucleic acid characterization in general. The chapter further involves the nuclear DNA reassociation that includes quantitation of the degree of gene sequence similarity between strains that became possible with the development of DNA reassociation techniques. These measure the extent of pairing of nucleotide sequences when DNA is made single-stranded, and then allowed to re-pair as a double strand. There are two basic methods. One is “free solution,” in which both DNAs of the test pair react while dissolved in a buffer solution, and the second relies on binding of one of the pair as single-stranded DNA to a matrix, such as a nitrocellulose filter, while the other strand of DNA remains free in the buffer surrounding the bound DNA.

Principles and Methods Used in Yeast Classification, and an Overview of Currently Accepted Yeast Genera

Yeasts are of benefit to mankind because they are widely used for production of foods, wine, beer, and a variety of biochemicals. Yeasts also cause spoilage of foods and beverages, and are of medical importance. At present, approximately 700 yeast species are recognized, but only a few are commonly known. Relatively few natural habitats have been thoroughly investigated for yeast species; consequently, we can assume that many more species await discovery. Because yeasts are widely used in traditional and modern biotechnology, the exploration for new species should lead to additional novel technologies.

Agriculturally Important Yeasts: Biological Control of Field and Postharvest Diseases Using Yeast Antagonists, and Yeasts as Pathogens of Plants

Publisher Summary This chapter discusses two important agricultural aspects of yeasts—control of plant diseases through application of yeasts as the control agent, and yeasts that are plant pathogens. Yeasts as biocontrol organisms are presented first, followed by a discussion of some of the more common plant pathogenic yeasts. In biocontrol, it is convenient to divide biotic diseases of plants into those in which the pathogen predominantly gains entrance to the plant via its underground parts versus those that infect aerial tissues of the plant. The vast majority of research on the biological control of plant diseases in the field using yeasts or yeast-like fungi has concentrated on diseases of above ground parts of plants. The potential of yeasts as biocontrol agents of soil-borne fungal plant pathogens is reviewed in the chapter. The use of yeasts to reduce decay on harvested commodities has also received considerable research attention. Application of yeasts for this purpose has been evaluated both as a pre- and as a postharvest treatment. Fruits are rich in easily utilizable carbon and are natural habitats for a variety of yeasts. Until recently, yeasts of grape and apple were studied most extensively because of their importance in vinification and making apple cider.

Chapter 34 – Kazachstania Zubkova (1971)

Publisher Summary This chapter studies the genus Kazachstania. Asexual reproduction is by multilateral budding on a narrow base. Cells are spherical, ovoid, or elongate. Pseudohyphae may be formed, but true hyphae are not produced. Colonies are smooth and white to tan in color. In sexual reproduction it is seen that asci may be unconjugated or show conjugation between independent cells or between a cell and its bud. Asci are persistent or deliquescent at maturity and produce 1–16 spherical, ovoid, or reniform ascospores. Ascospore surfaces may be roughened or smooth. In physiology and biochemistry it is seen that species are generally characterized by restricted responses to the standard tests used in yeast taxonomy. The chapter further examines the phylogenetic placement. The type of species mentioned is Kazachstania viticola. The species accepted are Kazachstania aerobia, Kazachstania africana, Kazachstania aquatica, Kazachstania barnettii, Kazachstania bovina, Kazachstania bulderi, and Kazachstania exigua. The systematic discussion of the species includes growth on YM agar, growth in YM broth, growth on the surface of YM broth, Dalmau plate culture on corn meal agar, formation of ascospores, CoQ, Mol% G1C, gene sequence accession numbers, type strain, cell carbohydrates, origin of the strains studied, systematics, ecology, biotechnology, agriculture and food, and clinical importance.

Automated UV-C Mutagenesis of Kluyveromyces marxianus NRRL Y-1109 and Selection for Microaerophilic Growth and Ethanol Production at Elevated Temperature on Biomass Sugars

The yeast Kluyveromyces marxianus is a potential microbial catalyst for fuel ethanol production from a wide range of biomass substrates. To improve its growth and ethanol yield at elevated temperature under microaerophilic conditions, K. marxianus NRRL Y-1109 was irradiated with UV-C using automated protocols on a robotic platform for picking and spreading irradiated cultures and for processing the resulting plates. The plates were incubated under anaerobic conditions on xylose or glucose for 5 mo at 46 °C. Two K. marxianus mutant strains (designated 7-1 and 8-1) survived and were isolated from the glucose plates. Both mutant strains, but not wild type, grew aerobically on glucose at 47 °C. All strains grew anaerobically at 46 °C on glucose, galactose, galacturonic acid, and pectin; however, only 7-1 grew anaerobically on xylose at 46 °C. Saccharomyces cerevisiae NRRL Y-2403 did not grow at 46 °C on any of these substrates. With glucose as a carbon source, ethanol yield after 3 d at 46 °C was higher for 8-1 than for wild type (0.51 and 0.43 g ethanol/g glucose, respectively). With galacturonic acid as a carbon source, the ethanol yield after 7 d at 46 °C was higher for 7-1 than for wild type (0.48 and 0.34 g ethanol/g galacturonic acid, respectively). These mutant strains have potential application in fuel ethanol production at elevated temperature from sugar constituents of starch, sucrose, pectin, and cellulosic biomass.

Adding yeasts with sugar to increase the number of effective insecticide classes to manage Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) in cherry

BACKGROUND Drosophila suzukii is a major pest of cherry in the western United States. We evaluated whether the addition of sugary baits could improve the efficacy of two classes of insecticides not considered to be sufficiently effective for this pest, diamides and spinosyns, in laboratory and field trials in cherry. RESULTS Adding cane sugar alone or in combination with the yeasts Saccharomyces cerevisiae or Aureobasidium pullulans significantly improved insecticide efficacy. However, the significance of adding yeasts to the sugar plus insecticide on fly mortality varied with respect to both the insecticide and yeast species. The addition of S. cerevisiae to sugar also did not significantly reduce egg densities in fruit compared with sugar alone. The addition of a yeast plus sugar significantly reduced egg densities in three field trials with cyantraniliprole and in two out of three trials with spinosad. CONCLUSION The addition of cane sugar with or without yeast can improve the effectiveness of diamide and spinosyn insecticides for D. suzukii in cherry. Inclusion of these two insecticides in D. suzukii management programs may alleviate the strong selection pressure currently being imposed on a few mode-of-action insecticide classes used by growers to maintain fly suppression over long continuous harvest periods of mixed cultivars. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.