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Modern Genomics: How to identify microbial species.

Created by George Rice, Montana State University

Classic methods dependent upon comparative morphology and culturing fall short for the following reasons -
  • Prokaryotes are incredibly diverse with relatively little morphological distinction (can't tell them apart under the microscope).
  • Fewer than 1% of the known microbes in any given environment can be cultured (the great plate anomaly).

The Answer - Molecular systemetics based upon 16s rRNA sequences (thanks to Carl Woese, the father of modern microbial systematics).

Sequence of the 16s gene.
A simplified map of the 16s rRNA gene. (courtesy of Bruce Fouke's lab)

Sequencing 16s rDNA from individual organisms has given us the ability map phylogenetic relationships between single celled organisms based upon how similar their 16s genes are. A classic example of this is shown below in the "Tree of Life" published by Norm Pace in 1997.

Norm Pase's 16s phylogenetic tree.
Norm Pace, 1997.

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