Desktop version

Home arrow Education

  • Increase font
  • Decrease font


<<   CONTENTS   >>

Taxonomy, Diversity, and Typing of Brewing Yeasts

Jose Paulo Sampaio1*, Ana Pontes1, Diego Libkind2 and Mathias Hutzler3

  • 1UCIBIO-REQUIMTE, Departamento de Ciencias da Vida, Faculdade de Ciencias e Tecnologia, Universidade Nova de Lisboa, Caparica, Portugal.
  • 2Laboratorio de Microbiologi'a Aplicada, Biotecnologi'a y Bioinformatica de levaduras, Instituto Andino-Patagonico de Tecnologi'as Biologicas y Geoambientales (IPATEC), Consejo Nacional de Investigaciones en Ciencia y Tecnica (CONICET ), Universidad Nacional del Comahue, Bariloche, Argentina.
  • 3Research Center Weihenstephan for Brewing and Food Quality, TU Munchen, Freising, Germany.
  • *Correspondence: This email address is being protected from spam bots, you need Javascript enabled to view it

https://doi.org/10.2177S/9781910190616.04

Abstract

The taxonomy and systematics of brewing yeasts have been a matter of debate and controversy since the early days of microbiology in the 1800s, when Saccharomyces cerevisiae and Saccharomyces carlsbergensis were first cultivated. The turbulent history of beer yeast systematics epitomizes the endeavours of yeast taxonomy since its origins when researchers used morphological characters and physiological traits to distinguish and classify species. The molecular revolution initiated in the 1980s exposed limitations of phenotypic methods, revealing numerous species synonyms and misclas- sifications. Today, DNA sequence data provide the means for accurate species identifications, strain typing, and phylogenetic classifications. Progress in the scientific knowledge of beer yeasts was also delayed by another level of complexity, which included inter-species hybridizations occurring in the brewing environment. Inter-species hybridizations created a plethora of chimeric genomes that could only be completely resolved when genomics entered the scene in the last two decades. Indeed, many key beer genotypes like S. pastorianus, the lager yeast, and S. bayanus, a beer contaminant, are complex multi-Saccharomyces species hybrids whose life history and ancestry are only now being revealed. Recently, a combination of novel genome sequencing approaches and microbial ecology studies solved decades-long disputes and revealed the wild genetic stocks of domesticated beer lineages. Here, we give an historical perspective of brewer's yeast taxonomy including also non-Saccharomyces yeast species and review available phenotypic and genetic-based typing methods for species and strain discrimination.

Introduction

Yeasts together with malt, water, and hops are an essential ingredient for beer. Their primary role is to convert sugars extracted from cereals into ethanol and carbon dioxide. Myriad other products of yeast metabolism are also essential for the unique sensorial characteristics that contribute to the final product. Studies on the history of beer and brewing have traced the ancestor of modern beers to cereal- based beverages produced in Ancient Egypt and in Mesopotamia circa 6,000 BC (Hornsey, 2003; McGovern, 2009). It is likely that the microorganisms that fermented those primeval beers were not radically different from those that we use today. For example, yeast cells were detected in Egyptian leavened bread dough dated 3.000 BC (Samuel, 1996;

2000) and molecular evidence for the presence of S. cerevisiae in wine fermentation has been obtained from pottery jars ofthe same period (Cavalieri et al., 2003).

The most relevant microorganisms for brewing are by far yeasts of the genus Saccharomyces. This genus includes also the yeast species that are essential for all the other processes that involve alcoholic fermentation. The best examples of such products are bread, wine and sake, but many other foods and beverages with a more local range of production and consumption, like palm wine or sorghum beer (Tapsoba et al., 2015), also rely on yeasts of the genus Saccharomyces.

Yeasts form a heterogeneous and artificial group of fungi that live predominantly in the unicellular stage and, similarly to other groups of microorganisms, lack distinct morphological traits (Kreger van Rij, 1987). Therefore, contrary to most plants or animals, yeasts are not only normally invisible to the naked eye but, when observed with a microscope, lack the distinctive morphological features that could allow the recognition of different species. Invisibility and lack of distinguishable micro-morphologies or other stable and phylogenetically coherent phenotypic markers, such as species-specific physiological properties, condemned yeasts, and microbes in general, to an unstable taxonomy. This contributed to consolidate, especially among the non-specialists, the belief that the recognition of the relevant yeasts for brewing was a daunting task, shadowed by disputed and conflicting taxonomic criteria and obscure nomenclature rules. In the period of more than 150 years from the first scientific records of yeasts by Cagniard-Latour, Ktitzing and Schwann in the 1830s (Barnett, 2004) to the generalization of DNA sequence data for taxonomy in the 1990s, a combination of methodologies that did not have the power to clearly differentiate species was employed in successive attempts at understanding yeast diversity and the species and lineages underlying it. Different approaches and different philosophies lead to frequent name changes that, for the most part, confounded those in industry or other applied fields that required at best a stable and logical nomenclature system. The age of enlightenment for microbial taxonomy was initiated when molecular sequence data were used to recognize species and to infer phylogenetic relationships, first for bacteria and archaea (Woese and Fox, 1977) and then for microscopic eukaryotes, with fungi being among the first to be investigated (e.g. Walker and Doolittle, 1982).

 
<<   CONTENTS   >>

Related topics