Yeasts

By: Jvo Siegrist, Analytix 2009, 5, 7.

Product Manager Microbiology ivo.siegrist@sial.com

A versatile organism with a diversified range of species ...

Yeast is one of the most important microorganisms known and utilised by mankind. Ancient Middle Eastern civilisations used the organism to bake bread and to produce mead, beer and wine.

Yeast is one of the best studied eukaryotic organisms and is often used in molecular biology as well as diverse other applications. It is the most frequently used organism for fermentation. Yeasts are unicellular fungi, although they sometimes build multicellular constructs known as pseudohyphae, or false hyphae. Most yeasts are not pathogenic; however there are certain strains that can cause infections in humans. In current technology, yeasts have an important role in the production of biofuels. The biomass from yeast is also used as a nutritional supplement or as a component of microbiological media. It is also an important source of vitamin B12.

The natural sources of yeast vary broadly. They may be found in the ocean, on the skin of humans and animals, and on the skins of fruit.

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Reproduction:

Yeasts have asexual and sexual reproductive cycles; however, the most common method for reproduction is asexual by budding or fi ssion. The nucleus of the parent cell splits and a daughter cell is built out of the parent cell and is separated.

The sexual reproduction method (meiosis) entails division of a diploid chromosome set and production of haploid spores, which then may conjugate with another cell to reform a diploid cell. However, haploid cells will generally die under stress, while spores can survive harsh conditions.

Table 1 Scientific classification and typical divisions (not complete)


There are diverse species of yeasts with a broad range of applications. While the majority of yeasts are benefi cial to humans and provide benefi ts such as biotechnological advancements, other unpleasant organisms may lead to infections or cause spoilage of fruit juices and alcoholic beverages. Some of the best-known yeast species with their respective descriptions are listed in the info box on the right-hand side.

  • Saccharomyces cerevisiae: also called budding yeast or baker’s yeast. Saccharomyces comes from the Greek term for sugar mould. The organism is also used as top-fermenting yeast in the brewery. It can ferment glucose, fructose, mannose, galactose, maltose, maltotriose, raffinose, and trehalose, but not lactose and cellobiose. The cells are round to ovoid and have a diameter of 5–10 micrometres. The organism reproduces by asexual reproduction called budding.
  • Saccharomyces carlsbergensis, Saccharomyces uvarum: bottom-fermenting yeasts, used for the production of lager beer; also ferments many sugars at low temperatures.
  • Candida albicans: an opportunistic pathogen that causes oral, intestinal and vaginal infections.
  • Candida utilis: used in the production of Kefir
  • Brettanomyces bruxellensis (Dekkera bruxellensis): spoilage organism in wine
  • Pichia pastoris: organism for biotechnological production of proteins (high growth rate and non-fastidious)
  • Malassezia furfur: responsible for skin problem (scurf)

     

Figure 1 Several baker’s yeast colonies on a microbiological medium


Media Brand Cat. No. Organisms/remarks
CaCO3 Agar Fluka 40545 yeast differentiation based on acid production from glucose
BiGGY Agar Fluka 73608 Candida albicans, Candida tropicalis.
Corn Meal Agar Fluka 42347 yeasts, fungal stock cultures, chlamydospore production by Candida albicans, mycel/pseudomycelium forming
Czapek Dox Agar Fluka 70185 fungi and yeasts, defined C-source and inorg. N-source
Dichloran Rose bengal Agar (Base) Fluka 17147 yeasts and moulds
EMB Agar Fluka 70186 rapid identification of Candida albicans, differentiation and identification of bacteria (E. coli, Aerobacter aerogenes, Staphylococci)
Levine EMB Agar Fluka 62087 rapid identification of Candida albicans, differentiation and identification of bacteria (E. coli, Aerobacter aerogenes, Staphylococci)
Lysine Medium Sigma L5910 wild yeasts in pitching yeasts, defined medium
Malt Agar Sigma M9802 yeasts and moulds
Malt Extract Agar Fluka 70145 yeasts and moulds
Malt Extract Agar modified, Vegitone Fluka 38954 yeasts and moulds
Malt Extract Broth Fluka 70146 yeasts and moulds
OGY Agar Fluka Fluka 75310 yeasts and moulds
Orange-serum Agar Fluka 75405 acid-tolerant spoilage microorganisms
Peptone Yeast Extract Agar Fluka 77196 yeasts and moulds
Potato Glucose Agar Fluka Fluka 70139
51684
yeasts and moulds
Potato Glucose Rose bengal Agar (Base) Fluka 17204 For promoting ascospore production
Potato Glucose Sucrose Agar Fluka 17205 Zygosaccharomyces rouxii
Rice Extract Agar Fluka 83551 yeasts, differentiation by chlamydospores and morphology
Rose Bengal Agar Base Fluka R1273 yeasts and moulds
Rose bengal Chloramphenicol Agar Fluka 17211 yeasts and moulds
Sabouraud 2 % Glucose Agar Fluka 84086 dermatophytes, fungi and yeasts
LSabouraud 4 % Glucose Agar Fluka 84088
40376
55277
cultivation of pathogenic and non-pathogenic fungi, especially dermatophytes
Sabouraud Glucose Agar with Chloramphenicol Fluka 89579 fungi and yeasts
Sabouraud Glucose Broth Fluka S3306 yeasts, moulds and aciduric bacteria
Sabouraud Maltose Agar Fluka S4181 dermatophytes, fungi and yeasts
SD Agar Fluka 84605 yeast
Tomato Juice Broth Fluka Fluka 17218 yeasts and other aciduric microorganisms
 
Table 2 Most common media for yeasts

For the detection, enumeration and cultivation of yeasts, the classical culture method is still needed. The media are in many cases very simple, as yeast is non-fastidious. Regarding selectivity, oxytetracyclin, gentamicin, chloramphenicol, rose bengal, chlortetracycline, and bismuth ammonium citrate at low pH conditions are often used. For diff erentiating the morphology of the colony, the microscopic image (budding, spore production, mycel/pseudo-mycelium forming) and biochemical reactions are used. An overview of some common media is given in Tables 2 and 3.

Media Brand Cat. No. Organisms/remarks
HiCrome™ OGYE Agar Base Fluka 66481 yeasts and moulds; C. albicans shows green and Sacch. cerevisiae colourless colonies
Candida Ident Agar Fluka 94382 Candida albicans (green), other yeasts (white, pink, beige), Gonnococci, moulds
 
Table 3 Chromogenic media for yeasts and moulds

Chromogenic media, one of the cleverest systems, provide a perfect solution for the selective isolation, diff erentiation and identifi cation of moulds and yeasts. With the aide of chromogenic substrates, certain characteristic enzymes are detected, and antibiotics inhibit bacterial growth. Diff erentiation is easy because of the diff erent colours of the colonies, depending on the species, caused by the ability to cleave diff erent chromogenic substrates (see Table 3 and Figure 2).

Figure 2 Candida Ident Agar, modified (Candida albicans = green-coloured smooth colonies, Candida tropicalis = blue to metallic blue-coloured raised colonies. Candida glabrata = cream to white, Candida krusei = purple coloured fuzzy colonies)


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New Detection Kits for Yeasts

The HybriScan® Test Kit is a new technology based on a rRNA probes sandwich method. It is possible to detect diverse species or a group of organisms at the same time if the appropriate probes are chosen. The test needs no PCR and is as simple as the ELISA test. It is a very robust system and detects only living cells, unlike the PCR. It is also possible to quantify the cell numbers with a colour reaction and microplate reader. The HybriScan®D Yeast kit was designed with a specifi c probe for yeasts of the family of Saccharomycetaceae. The HybriScan®D Drink kit detects additional beverage-spoiling bacteria.

More information about the theoretical background of the system, additional kits available, and much more, can be found under sigma-aldrich.com/hybriscan

Product Description Tests Brand Cat. No.
HybriScan®D Yeast 96 Fluka 61397
Specificity: yeasts including genera Zygosaccharomyces, Saccharomyces, Candida, Dekkera, Torulaspora and Pichia
HybriScan®D Drinks 96 Fluka 68301
Specificity: amongst other yeasts of the genera Saccharomyces, Zygosacchromyces, Brettanomyces, Torulaspora, Pichia, Candida and bacteria of the genera Lactobacillus, Acetobacteraceae and Alicyclobacillus
 
Table 4 HybriScan Kits for detection of yeast species

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Materials

     

References

  1. Balasubramanian M.K., Bi. E., Glotzer M. “Comparative Analysis of Cytokinesis in Budding Yeast, Fission Yeast and Animal Cells”. Curr. Biol. 14 (18) (2004).
  2. Yeong F.M., ”Severing All Ties Between Mother and Daughter: Cell Separation in Budding Yeast”. Mol. Microbiol. 55 (5), p. 1325–31 (2005).
  3. Neiman A.M.,”Ascospore Formation in the Yeast Saccharomyces cerevisiae”. Microbiol. Mol. Biol. Rev. 69 (4), p. 565–84 (2005).

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