The three domains of life

According to modern taxonomy, life on this planet can be grouped into three branches or domains—the Eukarya, the Bacteria, and the Archaea (Figure 2-1).This organization for classifying all living organisms was proposed and established in the 1980s by Carl Woese and is based on the relatedness of specific 16S rRNA sequences using a technique called oligonu-cleotide cataloging.This three-branch tree of life displaced the classical taxonomy that had recognized only two groups, eukaryotes and pro-karyotes, and that was based primarily on morphology and biochemical attributes. All of the microorganisms relevant to fermented foods (and food microbiology, in general) belong to either the Eukarya or Bacteria. The Archaea, while interesting for a number of reasons, consists of organisms that generally live and grow in

Entamoebidae

Entamoebidae

Phylogenetic Tree Three Domains Life

Figure 2-1. Phylogenetic tree of life (based on 16S rRNA sequences). Courtesy of the Joint Genome Institute (U.S. Department of Energy).

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Chloroflexi

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Figure 2-1. Phylogenetic tree of life (based on 16S rRNA sequences). Courtesy of the Joint Genome Institute (U.S. Department of Energy).

extreme environments (e.g., very high temperature, very low pH, very high salt), but rarely are they associated with foods.

Classification of organisms as eukaryotic or prokaryotic is based on a variety of characteristics (Bergey's Manual lists more than 50 cytological, chemical, metabolic, molecular, and reproductive properties), but the traditional distinguishing feature is the presence of a nuclear membrane in eukaryotes. Included within the Eukarya domain are animals, plants, protists, and fungi.The latter are represented by the Kingdom Fungi, which includes both yeasts and molds.

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Brew Your Own Beer

Discover How To Become Your Own Brew Master, With Brew Your Own Beer. It takes more than a recipe to make a great beer. Just using the right ingredients doesn't mean your beer will taste like it was meant to. Most of the time it’s the way a beer is made and served that makes it either an exceptional beer or one that gets dumped into the nearest flower pot.

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