Classification of Prokaryotes

Exam 2

Domain bacteria:

Cells lack nuclei (prokaryotic)

Unicellular

Have peptidoglycan

Divide by binary fission

Most common shapes are cocci, bacilli, or spiral

Domain archaea:

Cells lack nuclei (prokaryotic)

Unicellular

Divide by binary fission

Some have flagella but do not have peptidoglycan

Domain eukarya

Cells contain nuclei (eukaryotic)

Unicellular or multicellular (primarily multicellular)

Include algae, fungi, protozoa, animals, and plants

Do not have peptidoglycan

Taxonomy

The branch of biology that deals with classification

Carl Linnaeus

Came up with the binomial nomenclature

Carl Woese

Introduced the most current 3 domain classification system

6 kingdoms

Archaea, bacteria, protista, fungi, plantae, animalia

Kingdom archaea

Consists of the most primitive and simplest organisms that do not have a nucleus and are known as prokaryotes. 

Kingdom bacteria

Consists of single celled organisms that do not have a nucleus (prokaryotes) (ex. e.Coli)

Kingdon protista

Consists of organisms that are mostly single celled with a nucleus (eukaryotes) (ex. green algae)

Kingdom fungi

Consists of non photosynthetic multicellular or unicellular organisms that cannot make their own food. They obtain their food from other organisms and digest it externally. (ex. yeast, mushrooms)

Kingdom plantae

Consists of photosynthetic multicellular organisms. They can make their own food (ex. algae, roses, oak trees)

Kingdom animalia

Consists of non photosynthetic multicellular organisms. They cannot make their own food (ex. humans, cats)

Domain (largest)

Collection of similar kingdoms

Kingdom

Collection of similar phyla

Phylum

Collection of similar classes

Class

Collection of similar orders

Order

Collection of similar families

Family

Collection of similar genera

Genus

Group of similar related species

Species (smallest)

Group of closely related strains

Identification

The process of identifying organisms to the species level using biochemicals

Classification

Arranging organisms into similar groups

Nomenclature

Assigning each organism with a genus and species name

Methods to identify and classify microorganisms:

Microscopic examinations

Culture characteristics

Biochemical tests

Nucleic acid analysis

Staining procedures used to classify and/or identify bacteria and bacterial structures:

Gram staining

Acid fast stain

Capsule stain

Flagella stain

Endospore stain

Serology

Uses specific interactions of antibodies and antigens. These tests are used for identification of pathogens

Nucleic acid probes

May be used in identification of organisms which cannot be grown in culture using polymerase chain reaction (PCR). This method amplifies sequences that are used for identification

Phage typing

Process used to identify bacteria using phages (bacterial viruses). This method has mostly been replaced by molecular methods

Antibiograms

Used to differentiate bacterial strains based on antibiotic susceptibility. Discs containing antibiotics are placed on plates inoculated by bacteria. Clear zone around a disc indicated microbial susceptibility. Different strains will have different susceptibility patterns. 

Sequencing

Comparison of 16s rRNA has revolutionized classification. Because of its very slow rate of mutation 16s rRNA identification process allows distant relatedness of organisms. 

DNA hybridization

Related organisms can be determined by similarity of nucleotide sequences. Sequence homology is measured by DNA hybridization. If two trains show high percentage of DNA hybridization they are considered related

DNA base ratio

Comparison of genomes to determine DNA base ratios. Looking at relative proportion of A:T and G:C bonding in DNA. Base ration is expressed in G:C content. If the G:C ratio deviates significantly the organisms are not related.