Classification of Microorganisms
is the science of the classification of organisms, with the goal of
showing relationships among organisms.
also provides a means of identifying organisms.
The Study Of Phylogenetic Relationships
is the evolutionary history of a group of organisms.
taxonomic hierarchy shows evolutionary, or phylogenetic, relationships
were separated into the Kingdom Prokaryotae in 1968.
organisms were divided into five kingdoms in 1969.
organisms are currently classified into three domains. A domain can be divided into kingdoms.
- In this
system, plants, animals, fungi, and protists belong to the Domain
(with peptidoglycan) form a second domain.
(with unusual cell walls) are placed in the Domain Archaea.
A Phylogenetic Hierarchy
are grouped into taxa according to phylogenetic relationships (from
a common ancestor).
of the information for eukaryotic relationships is obtained from the
relationships are determined by rRNA sequencing, although some fossils
of prokaryotes exist. (Figure
to scientific nomenclature, each organism is assigned two names, or
binomial : a genus and a specific epithet, or species.
for the assignment of names to bacteria are established by the International
Committee on Systematic Bacteriology.
for naming fungi and algae are published in the International Code
of Botanical Nomenclature.
for naming protozoa are found in the International Code of Zoological
The Taxonomic Hierarchy
- A eukaryotic
species is a group of organisms that interbreeds but does not breed
with individuals of another species.
species are grouped into a genus; similiar genera are group into a
family; families into an order; orders into a class; classes into
a division or phylum; phyla into a kingdom; and kingdoms into domains.
Classification of Prokaryotes
Manual of Systematic Bacteriology is the standard reference on bacterial
- A group
of bacteria derived from a single cell is called a strain.
related strains constitute a bacterial species.
10.4, Figure 10.6
Classification of Eukaryotes
organisms may be classified into the Kingdom Fungi, Plantae, or Animalia.
are mostly unicellular organisms; these organisms are currently being
assigned to kingdoms.
are absorptive chemoheterotrophs that develop from spores.
photoautotrophs are placed in the Kingdom Plantae.
ingestive heterotrophs are classified as Animalia.
Classification of Viruses
are not placed in a kingdom. They
are not composed of cells and cannot grow without a host cell.
- A viral
species is a population of viruses with similar characteristics that
occupies a particular ecological niche.
Methods Of Classifying And Identifying Microorganisms
s Manual of Determinative Bacteriology is the standard reference for
laboratory identification of bacteria.
characteristics are useful in identifying microorganisms, especially
when aided by differential staining techniques (Gram staining and
acid fast stains can suggest a course of treatment before the organism
is positively identified).
presence of various enzymes, as determined by biochemical tests, is
used in identifying microorganisms.
10.8) Rapid identification can be accomplished with specific sets
of biochemical tests. (Figure
tests, involving the reactions of microorganisms with specific antibodies,
are useful in determining the identity of strains and species, as
well as relationships among organisms.
Slide agglutination (Figure
10.10), ELISA (Figure 10.11),
and Western blotting (Figure
10.12) are examples of serological tests.
typing is the identification of bacterial species and strains by determining
their susceptibility to various phages.
acid profiles can be used identify some organisms.
cytometry measures physical and chemical characteristics of cells.
percentage of GC base pairs in the nucleic acid of cells can be used
in the classification of organisms.
number and sizes of DNA fragments, or DNA fingerprints, produced by
restriction enzymes are used to determine genetic similarities.
sequence of bases in ribosomal RNA can be used in the classification
polymerase chain reaction (PCR)
can be used to detect small amounts of microbial DNA in a sample.
strands of DNA and RNA, from related organisms will hydrogen-bond
to form a double-stranded molecule; this bonding is called nucleic
blotting and DNA probes, including DNA chips, are examples of hybridization
10.16, Figure 10.17)
Summary: (Figure 10.18)
keys are used for the identification of organisms. Cladograms show phylogenetic relationships