Alessandro Martini

Saccharomyces Meyen ex Reess

Publisher Summary This chapter focuses on Saccharomyces genus and its member species. The cells of this genus are globose, ellipsoidal, or cylindroidal. Vegetative reproduction occurs through multilateral budding, and pseudohyphae may be formed but not septate hyphae. The vegetative phase is predominantly diploid (or of higher ploidy) and conjugation occurs on or soon after germination of the ascospores. The ascospores are globose to short ellipsoidal, with a smooth wall and usually one to four per ascus. The member species of this genus include Saccharomyces barnettii, Saccharomyces bayanus, Saccharomyces castellii, Saccharomyces cerevisiae, and Saccharomyces dairenensis. The cells of Saccharomyces barnettii species, after a growth in 5% malt extract at 25° C for three days appear as globose, ovoidal, or elongate. The vegetative cells of this species are transformed directly into persistent asci containing one or two, and rarely four, globose to short ellipsoidal ascospores. The ascospores were observed on acetate agar usually after 20-40 days at 25° C. The cells of Saccharomyces bayanus species, after growth in 5% malt extract for 3 days at 25° C, are globose, ovoidal, or elongate and are usually isolated. The vegetative cells are transformed directly into persistent asci containing one to four globose to short ellipsoidal ascospores.

Origin and domestication of the wine yeast Saccharomyces cerevisiae

Recent ecological evidence points to a circulation model for Saccharomyces cerevisiae in nature which is different from that proposed at the end of the last century. The wine yeast ‘par excellence’ is isolated with extreme difficulty from conventional habitats, such as vineyard soil or the surface of ripe grapes, while it is almost the only species colonising the surfaces of the winery equipment.

Facts, myths and legends on the prime industrial microorganism

SummaryArchaic speculations and firmly established legends regarding the origin of the yeastSaccharomyces cerevisiae and related species are revisited in light of past and recent ecological evidence pointing to a strict association with artificial, man-made environments such as wineries and fermentation plants. The nomenclature within this industrially important group is also discussed in view of the modifications imposed from application of molecular techniques to classification.

Electrophoretic karyotyping as a taxonomic tool in the genus Saccharomyces

SummaryThe electrophoretic karyotypes of strains of the ten species of the yeast genusSaccharomyces (sensu Vaughan-Martini & Martini 1992) were determined by the CHEF (contour-clamped homogeneous electric field) system of pulsed field gel electrophoresis. The number of bands was found to vary from 6 to 17 and the calculated molecular weights of haploid genomes ranged from 7.9 to 14.6 Mbp. The type strains ofS. exiguus and the four species of theSaccharomyces sensu stricto complex (S. bayanus, S. cerevisiae, S. paradoxus andS. pastorianus) have genomes comprised of chromosomes of all three size classes: light (< 500 kb), medium (500–1000 kb) and heavy (> 1,000 kb).Saccharomyces kluyveri DNA has only heavy bands, while the remaining species exhibit medium and heavy chromosomes. When more than one strain of each species was examined, it was seen that while the speciesS. bayanus, S. castellii, S. cerevisiae, S. kluyveri, S. paradoxus andS. pastorianus showed uniform karyotypes,S. dairensis, S. exiguus, S. servazzii andS. unisporus comprise heterogeneous taxa.

Production of carotenoids by strains of Rhodotorula glutinis cultured in raw materials of agro-industrial origin

The production of carotenoids by strains of Rhodotorula glutinis on different raw materials of agro-industrial origin (grape must, glucose syrup, beet molasses, soybean flour extract, maize flour extract) was investigated. Maximum yield (5.95 mg/l of total carotenoids culture fluid, 630 μg/g dry cell weight) was obtained with a particular strain of Rhodotorula glutinis after a batch culture of 120 h in a substrate containing concentrated rectified grape must as the sole carbohydrate source. In all experiments, the major pigments forming carotenoids (β-carotene, torulene, torularhodin) were quantified.

Yeast flora of grape berries during ripening

The yeast flora associated with the surface of grapes during ripening was studied with regard to different sectors of the grape skin and the position in the bunch by means of traditional as well as more vigorous preisolation and precounting treatments. The yeast number per square centimeter of skin increases with ripening and is highest in the area immediately surrounding the stem. The cluster sector closer to the peduncle seems to constitute a favorable substrate for yeasts, hosting a resident flora about 10 and 100 times higher than the central and lower parts of the bunch, respectively.Kloeckera apiculata was the normal resident species of grapes regardless of the sector or the ripening period, and constitutes the fermenting flora of mature grapes. The ecological implications of the results of this survey are discussed.

A Taxonomic Key for the Genus Saccharomyces

Summary Complete physiological analyses of eighty-six strains of the ten recognized species of the genus Saccharomyces were performed with the scope of establishing a reliable taxonomic key. Results showed that it is possible to clearly distinguish strains of the species Sacch. bayanus, Sacch. cerevisiae, Sacch. kluyveri, Sacch. paradoxus, Sacch. pastorianus, Sacch. servazzii and Sacch. unisporus . Some difficulties can be encountered in the classification of strains of Sacch. dairensis and Sacch. exiguus which probably comprise heterogeneous taxa.

Electrophoretic Karyotypes of Authentic Strains of the Sensu Stricto Group of the Genus Saccharomyces

A comparative electrophoretic karyotyping study was performed with several certified authentic strains of the four species that could be distinguished by nuclear DNA (nDNA)-nDNA reassociation data within the sensu stricto group of the genus Saccharomyces. A multivariate analysis of the polymorphisms observed in pulsed-field gel electrophoretic profiles (numbers and molecular weights of separated units) revealed that the strains could be separated into four clusters that corresponded to the taxa that were distinguished on the basis of nDNA comparisons. Discrepancies between nDNA reassociation data and membership in the corresponding clusters were observed only with two strains of Saccharomyces paradoxus. Blind tests carried out with additional industrial strains confirmed the general validity of the statistical model created for comparison of karyotypes within the species included in Saccharomyces sensu stricto.

Systematics of the species of the yeast genus Saccharomyces associated with the fermentation industry

SummaryThe so-called wine yeasts Saccharomyces cerevisiae, S. chevalieri, S. bayanus, S. italicus and S. uvarum are characterized by high ethanol tolerance and fermentation velocity. They are ecologically related, being predominantly associated with grape must and wine, and are taxonomically indistinguishable. The only significant physiological differences are between the ability to ferment certain sugars. A taxonomic revision of more than 1,000 strains isolated during the past 50 years and belonging to the above species showed extreme instability in the ability to ferment different sugars. The relationships between these yeasts were examined for DNA base composition and DNA-DNA reassociation. The G+C ranged from 37.6% to 39.0% while optical reassociation experiments defined a first group of species (Saccharomyces cerevisiae, S. chevalieri and S. italicus) exhibiting high base sequence complementarity (>90%). S. bayanus and S. uvarum also showed a high degree of relatedness. Low homology values (∼30%) indicate that the two groups of species are not closely related. While it is proposed to combine S. cerevisiae, S. chevalieri and S. italicus into one single species under the oldest epithet Saccharomyces cerevisiae, a study of a larger number of strains is recommended before considering the taxonomic position of S. bayanus and S. uvarum.

Taxonomic revision of the yeast genus Kluyveromyces by nuclear deoxyribonucleic acid reassociation

Deoxyribonucleic acid relatedness among the type strains of all taxa and known anamorphs assigned to the yeast genus Kluyveromyces was assessed by the optical reassociation technique. Three groups of species related at the 95% level or higher were found: (i) K. lactis including K. drosophilarum, K. phaseolosporus, K. vanudeni, and the anamorph Candida sphaerica; (ii) K. marxianus with K. bulgaricus, K. cicerisporus, K. fragilis, K. wikenii, and the anamorphs Candida kefyr, Candida macedoniensis, and Candida pseudotropicalis; (iii) K. thermotolerans with K. veronae and the anamorph Candida dattila. The remaining species, including the recently described K. blattae and K. waltii, are not related to each other or to the members of the above three groups. The nomen nudum K. cellobiovorus is not conspecific with any of the species of the genus. The species assignment obtained by nuclear deoxyribonucleic acid reassociation does not entirely conform with the previously proposed reorganization of the genus Kluyveromyces (J.-P. van der Walt and E. Johannsen, p. 224–251, in N. J. W. Kreger-van Rij, ed., The Yeasts. A Taxonomic Study, 1984).