c17 lecture 3

Taxonomy vs phylogeny

T: Phenetic organization, based on phenotypes

P: Based on evolutionary relationships

Polyphasic Taxonomy

Incorporates various phenetic and phylogenetic information, with 16S RNA analysis

Ferdinand Cohn

Father of Bacteriology

Sorted bacteria based on morphology

Robert Koch on bacterial species designation:

Bacteria that maintain the characteristics when cultured in the same conditions should be designated a species

Biological classification


How do we define species for prokaryotes?

- Prokaryotes lack sexual reproduction -> cant use interbreeding

- Collection of strains, housekeeping genes


Differ biochemically and physiologically


Differ morphologically


Differ in antigenic properties

Type strain

First strain isolated, used as a reference

Binomial system of nomenclature for microbes

Genus species

G. Species


Pathogenic strain of bacteria after recieving new genetic information through HGT

Phenetic classification system for microbes

Based on as many characteristics as possibleMorphologicalPhysiologicalEcologicalMolecular

Ecological characteristics of a microbe

Life cycle patternsSymbiotic relationshipsPathogenic abilityHabitatGrowth Requirements

6 analysis methods of molecular taxonomy

1) Nucleic acid base composition2) Nucleic acid hybridization3) Nucleic acid sequencing4) Genomic fingerprinting5) Proteins6) Fatty acids

G+C variation among prokaryotes


G+C variation among a genus


Hybridization percentage and interpretation

0-25% = different genera25-75% = same genus, different species75-100% = same species

Most powerful and direct method for comparing genes and genomes?

Nucleic acid sequencing

3 main problems with phylogeny in microbes

1) Taxonomy not based on evolutive relationships

2) Asexual reproduction + HGT

3) No fossil record to support evolutive taxa