Classification of microbes (and other living things)

Major events in the history of life:life was originally microscopic and

unicellular

Taxonomy: the science of naming and classifying organisms (Carolus Linnaeus)

Phylogeny: evolutionary history

Systematics: the science of classification basedon evolutionary history of organisms

Linnaean classification system is used today (with modifications)

• Binomial (“scientific name”)– Genus and species

names (specific epithet)

• Hierarchical classification

How is classification achieved?

• Observation– Similarities and differences– Fossil record

• Molecular analysis – DNA – Ribosomal RNA– Mitochondrial DNA– Proteins

Ideas about classification have changed

• Linnaeus- plants and animals (1735)• Where do bacteria and fungi belong?

– Von Nägeli- with plants (1857)– Haeckel- Kingdom Protista (1866)

• Whitaker – five kingdoms (1969)• Woese- domains (1978)

Classification may change again

Classification by RNA sequence data

Phenotypes (physical differences) between the domains

Classification of prokaryotes

• Morphology (Gram-staining)• Nutrition• Metabolism• Environmental niche• rRNA sequences (all living cells have them)• Reference: Bergey’s Manual of Systematic

Bacteriology; Bergey’s Manual of Determinative Bacteriology)

• Most prokaryotes have not been discovered!

Microbial identification

• Differential media• Biochemical testing• Serology• Phage typing• Genetic testing

– rRNA sequencing

A dichotomous key

• Classic tool for identification

• Most of these tests can be administered simultaneously

• Different keys can be developed for groups of bacteria

How do you make bacteria look different?

Genomic analysis Phage typing

Archaea: “extreme bacteria”

• Discovered in late 1970’s• Species live at extreme temperature, pH,

have unusual metabolic properties• Hard to study

Classification of eukaryotes• Plantae- mosses, ferns, conifers, flworing plants

(some algae)– multicellular, photosynthetic

• Animalia- sponges, worms, various vertebrates and invertebrates– multicellular, ingest nutrients

• Fungi (1959)- yeasts, molds, mushrooms– Absorb nutrients, form hyphae if multicellular

• Protists- unicellular organisms– Don’t fit anywhere else!

Classification of viruses

• Not cellular, so are not classified in hierarchical system

• Viral species- population of viruses with similar characteristics and that occupy a particular ecological niche

Summary

• Eukaryotes are much more diverse than prokaryotes

• Some have evolved much more recently than others

• All are “successful” in their niche• Classification is an ongoing process• Genetic and phenotypic differences are

considered in classification