Key Concepts for Chapter 19

These are the most important concepts you are learning in this chapter:

1. In order to make sense of the diversity of organisms, it is necessary to group similar organisms together and organize these groups in a nonoverlapping hierarchical arrangement. Taxonomy is the science of biological classification.

2. It appears that the procaryotic groups (archaeobacteria and eubacteria) first developed, then the eukaryotes. This resulted in three domains or empires: Eubacteria (Bacteria), Archaea, and Eucarya. These domains differ from one another in rRNA sequences and many other ways.

3. The basic taxonomic group is the species, which is defined in terms of either sexual reproduction or general similarity.

4. Classifications are based on an analysis of possible evolutionary relationships (phylogenetic or phyletic classification) or on overall similarity (phenetic classification). The results of these analyses are often summarized in treelike diagrams called dendrograms.

5. Morphological, physiological, metabolic, ecological, genetic, and molecular characteristics are all useful in taxonomy because they reflect the organization and activity of the genome. Nucleic acid sequences are probably the best indicators of microbial phylogeny and relatedness because nucleic acids are either the genetic material itself or the products of gene transcription.

6. The first edition of Bergey’s Manual of Systematic Bacteriology is largely phenotypic and divides the bacteria into groups based on easily determined characteristics such as shape, Gram-staining properties, oxygen relationships, and motility. The second edition, with its five volumes and 30 sections, will be phylogenetically organized and distribute procaryotes among two domains and at least 14 kingdoms.

7. Bacterial taxonomy is rapidly changing due to the acquisition of new data, particulary the use of molecular techniques such as the comparison of ribosomal RNA structure and chromosome sequences. This is leading to new phylogenetic classification.

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