- Bacteriahave a cell wall composed of peptidoglycan and muramic acid.
Bacteria also have membrane lipids with ester-linked, straight-chained
fatty acids that resemble eukaryotic membrane lipids. Most prokaryotes
are bacteria. Bacteria also have plasmids, which are small, double-stranded
DNA molecules that are extrachromosomal. - Eukarya are of the domain eukarya and have a defined nucleus and mem-
brane bound organelles.
TAXONOMIC RANK AND FILE
A taxonomy has an overlapping hierarchy that forms levels of rank orcategory
similar to an organization chart. Each rank contains microorganisms that have sim-
ilar characteristics. A rank can also have other ranks that contain microorganisms.
Microorganisms that belong to a lower rank have characteristics that are asso-
ciated with a higher rank to which the lower rank belongs. However, character-
istics of microorganisms of a lower rank are not found in microorganisms that
belong to the same higher rank as the lower-rank microorganism.
Microbiologists use a microbial taxonomy(Fig. 9-3), which is different from
what biologists, who work with larger organisms, use. Microbial taxonomy is
commonly called prokaryotic taxonomy. The widely accepted prokaryotic tax-
onomy is Bergey’s Manual of Systematic Bacteriology,first published in 1923 by
the American Society for Microbiology. David Bergey was chairperson of the
editorial board.
In the taxonomy of prokaryotes, the most commonly used rank (in order from
most general to most specific) is:Domain
Kingdom
Phyla
Class
Order
Family
Genus
Species
The basic taxonomic group in microbial taxonomy is the species. Taxonomists
working with higher organisms define their species differently than microbiolo-
gists. Prokaryotic species are characterized by differences in their phenotype and(^144) CHAPTER 9 Classification of Microorganisms