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Symposium: “Herman Phaff: Learning from Yeast” Santiago de Compostela, Spain, 23–24 September 2003

Alessandro Martini, Ann Vaughan-Martini
DOI: http://dx.doi.org/10.1016/j.femsyr.2004.06.005 889-890 First published online: 1 September 2004

Thomas Gonzàlez Villa, Professor of Microbiology at the University of Santiago de Compostela and former postdoctoral fellow in the laboratory of Herman J. Phaff, in conjunction with the Fundación Ramón Areces, organized a symposium in memory of the former Professor at the University of California, Davis. The symposium, held during the 29th annual meeting of the Spanish Society for Microbiology (SEM), offered a panoramic view of Phaff's enormous contributions to the knowledge of yeast biology, taxonomy and ecology. Seminars were presented by former Phaff students and postdocs covering various aspects of yeast research originated and associated with the stay in Davis, while some Spanish yeast scientists discussed investigations indirectly inspired by Phaff.

Introductory remarks were made by Thomas Villa, Carlos Hardisson, President of the Spanish Society of Microbiology, and Julio Villanueva for the Fundación Ramón Areces.

Then Arnold Demain (R.I.S.E.-Drew University, Madison, NJ) began with a moving review of Phaff's career: “Herman Jan Phaff: professor, mentor, friend and colleague”. Phaff left the family wine-trade in Winschoten, The Netherlands, to pursue a degree in Chemical Engineering at the Technical University of Delft under Albert Jan Kluyver. This was followed by a move to the United States and a brilliant career, first at University of California, Berkeley, and then at UC Davis. This seminar, together with that of Sally Ann Meyer (Georgia State University): “Beer, bread and beyond”, offered a very human picture of a great yeast scientist. Phaff was remembered as an inexhaustible worker, a stickler for details, a global scientist and a “human yeast encyclopedia”. At the same time, he was readily available for useful advice, and offered a friendly home atmosphere during the renowned parties that he and his wife Marinka regularly gave for students over the years.

AndréLachance (University of Western Ontario, London, Canada) reviewed: “The Phaff school of yeast ecology”, pointing out that although Phaff's work spanned the whole gamut of yeast biology, his most original contribution was to the understanding of the position of yeasts in nature. Six focal points of the “Phaff approach” were resumed as: (1) yeasts as such are a sufficient object of study; (2) species must be correctly identified in order to have a clear idea of a yeast community; (3) adequate sample size is essential for deriving ecologically meaningful conclusions; (4) the bacteriological dictum “everything is everywhere” does not necessarily apply to yeast distribution; (5) the cornerstone of yeast ecology is the habitat; and (6) the most exciting aspect of yeast biology is ecology.

Eric Johnson (University of Wisconsin, Madison, WI, USA) in “Phaffia rhodozyma: a colorful odyssey” discussed the interesting biotechnological aspects of a yeast isolated by Phaff and associates in the 1960s. The use of Phaffia rhodozyma (and its teleomorphic state Xanthophyllomyces dendrorhous) as pigment sources in aquaculture of salmonids and lobsters, as well as for the coloration of chicken and quail egg yolks, is one the most successful industrial applications of yeasts. The pigment, astaxanthin (3,3′-dihydroxy-β,β-carotene-4,4′dione), widely studied since its discovery in the 1970's, has been shown to protect P. rhodozyma from damage by reactive oxygen species. Over the years Johnson and his group have studied the nutritional and environmental conditions which regulate astaxanthin biosynthesis in P. rhodozyma.

Ann Vaughan-Martini (University of Perugia, Italy) discussed another Phaff passion: correct yeast identification, in “Reflections on what Herman Phaff taught us about taxonomy and classification of yeasts for different end users in biotechnology, ecological studies or medicine”. The approach to yeast identification has changed radically since the early years of Phaff's career with the advent of molecular taxonomy and the enormous advances in laboratory technology. As a consequence, while some conventional methods can still be validly applied, many molecular techniques have been developed which allow for strain classification on all taxonomic levels. It is only after a critical evaluation of the actual scope of each identification procedure that one can determine the most appropriate use of the many protocols now available.

Enrique Herrero (University of Lérida, Spain) offered an overview of recent progress following the complete sequencing of the genomes of Saccharomyces cerevisiae, Candida albicans and Schizosaccharomyces pombe, with: “Comparative genomics of yeast species: new insights into their biology”. The sequencing of these and other Hemiascomycetes provides important information regarding the evolutionary relationships between yeast species. It has been shown that gene order conservation is progressively lost as phylogenetic distance increases, even though gene function seems to have been much more conserved during evolution. The finding that C. albicans has a larger number of species–specific genes with respect to S. cerevisiae and Sch. pombe could possibly account for some of the peculiar biological characteristics of this dimorphic yeast.

The second day of the symposium was initiated with an overview of industrial applications of yeasts presented by Arnold Demain in collaboration with JoséAdrio (Puleva Biotech, Granada, Spain), entitled: “Fungal biotechnology”. Even though the biotechnological application of fungi and yeasts surely goes back to prehistoric times, the twentieth century could be considered the golden age of industrial microbiology with a myriad of fermentation products (solvents, antibiotics, enzymes, vitamins, etc.) now available. This trend received even more impetus with the advent of molecular biology as yeast and molds came to be used as microbial “cell factories” for the production of homologous and heterologous proteins and other metabolites. Finally, the best is yet to come as genomes of additional species are sequenced, and gene and protein arrays become available.

Amparo Querol, with “Molecular evolution of yeasts of biotechnological interest” offered an intriguing prospective on the “domesticated” species of Saccharomyces and Kluyveromyces which, due to millennial use in various food fermentations, have undergone an accelerated evolution as opposed to strains living in natural environments. Molecular studies on genomic and mitochondrial DNA sequences have shown that multiple hybridizations have occurred between industrial species of the Saccharomyces sensu stricto complex, leading to progeny with variably composed genomes coming from two or more parents. Similar mechanisms of adaptive evolution appear to have also occurred in K. lactis strains associated with the microbial transformation of milk products.

Alessandro Martini (University of Perugia, Italy) discussed recent studies confuting the long-maintained Pasteur hypothesis regarding the natural (vineyard) origin of wine strains of S. cerevisiae with “Biotechnology of natural and winery-associated strains of Saccharomyces cerevisiae”. The Querol proposal regarding adaptive evolution in industrial strains was supported by the results of experiments comparing the enological characteristics of different S. cerevisiae strains isolated from natural and winery environments. The winery-isolated strains exhibited exceptional enological properties, as well as a capacity to produce an assortment of volatile compounds specific to various Italian DOC zones. These results indicate that the domestication of these strains has led to the formation of particularly favorable characteristics useful for special biotechnological transformations, and offers an interesting prospective as to the utility of isolating autochthonous strains to be used as locality-specific starters for the wine industry.

The symposium was closed with a final seminar by Mariano Gacto regarding research done in collaboration with Thomas Villa, which discussed: “Learning from yeasts: intracellular sensing of stress conditions”. This investigation sought to determine how cells respond to stress and distinguish between different stressing stimuli. Studies on the stress-activated protein kinase (SAPK) pathways and related mechanisms provide insight into the biochemistry that regulates signal transmission and leads to cell adaptation and differentiation. Sch. pombe was chosen as a model system since it has been found to be more closely related to higher eukaryotes than budding yeasts, thus offering a more significant approach to solving biological issues relevant to mammalian cells.

Full manuscripts of most of these seminars have been recently published in a special edition of International Microbiology (volume 6(3): 155–219, September 2003), the official journal of the Spanish Society for Microbiology (http://www.IM.microbios.org).

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