Prokaryotic Organisms

    Before the invention of the electron microscope, cells were generally classified as either plant cells or animal cells. The reason for this, is that plant and animal cells are relatively large eukaryotic cells that could be easily seen using the magnifying power of the compound light microscope. As science and technology continued to advance, smaller cells were discovered. These included protists, fungi and bacteria. 
   

    The invention of electron microscopy, ushered in a new age of microbiology.  With the ability to peer into even the tiniest prokaryotic cells, scientists were able to make comparisons between different cells and different life forms like never before. ​

    Then... There Were 3

   In 1977, evolutionary biologist Carl Woese, discovered a new type of cell that existed as a single-celled organism. Carl Woese made this discovery during his work comparing the nucleotide sequences of different types of cells, to uncover phylogenic relationships. 

    The nucleotide sequences that Carl Woese examined were those that formed the gene that codes for the ribosomal RNA (rRNA) which forms the small ribosomal subunit. Woese's work not only found a fundamental difference between prokaryotic cells and eukaryotic cells, but he also found that prokaryotic cells were divided into 2 distinct groups possessing unique morphological and physiological characteristics. ​​

Small subunit ribosomal RNA, 5' domain taken from the Rfam database. This example is RF00177

   Bacteria cells were known at the time, but there was another type of cell that was distinctly unique from both the eukaryotic cells and the bacteria cells. Carl Woese originally called this newly discovered group of single-celled organisms archaebacteria, which translates to "ancient bacteria". There was a campaign to change the taxonomic structure of the day to include a third domain for the archaebacteria.   

   

Phylogeny is a diagrammatic hypothesis (giving us our phylogenic tree) about the history of the evolutionary relationships of a group of organisms, based on DNA evidence, morphological and physiological characteristics. 

The English Spelling for Eukaryotic and Prokaryotic is "Eucaryotic" and "Procaryotic"

Taxonomy the word taxonomy comes from the Greeks words meaning "method" and "arrangement".  It is the science of categorizing, defining and naming groups of organisms based on common genetic, morphological, and/or physiological characteristics. 

Bacteria

Archaea

    Following the initial discovery of disparity in the small ribosomal subunit of archeabacterial cells (now called archaeal cells), more differences were soon elucidated, confirming the uniqueness of the organisms belonging to this new category. Some of these differences include...

1. differences in cell wall composition
2. differences in lipids that form the cell membrane
3. differences in sensitivities to antibiotics
4. lipids, and sensitivity

   Eventually, in light of the overwhelming scientific evidence, the taxonomic structure was finally reorganized into the 3-domain system we know today. To further distinguish the archaebacteria as a separate domain from bacteria, the name was changed to simply, "archaea". 

Nomenclature

​    There are a multitude of life forms on our planet. New species are being discovered all of the time. The convenience of categorization, is that it assists us in communicating.  Could you image having to explain an organism to someone who has never seen it before without using categories?  Supposed this person wanted specific information about how the organisms metabolizes or reproduces. When we can employ the use of categories, if I describe an organism to someone and I mention that it is a "plant", this gives the listener a lot of great information about that organism from the use of just a single simple word! Cool!

    Species are assigned a scientific name (or binomial name or Latin name) according to their classification. These names are composed two words. The first word is the genus and the second word is the specific epithet. The genus and epithet together define the species. The epithet, in this context, is defined broadly an adjective expressing a quality or attribute of the organism. The names are typically odd-sounding and tongue-twisting and are often derived from Latin. Occasionally a species will be named in honor who discovered it, or the location in which it was discovered. ​

   Nomenclature Examples

Escherichia coli

• Escherichia coli was named after Theodore Escherich who first identified the common bacteria in stool. 

• Neisseria gonorrhoeae was named after Albert Neisser who first discovered it. 

​Some names are derived from the Latin terms that relate to their shape or physical appearance.

• Vibrio cholerae was named "vibrio" which means “comma-shaped,” because it resembles the shape of a comma.

​Vibrio cholerae

• Staphylococcus aureus received its name from the Latin words "staphylo-", which means "clusters" and "coccus", which means "round", due to its appearance that somewhat resembles clusters of round grapes. 

Neisseria gonorrhoeae

Staphylococcus aureus

Other names can be based on the physiological or chemical attributes or the organism. For example, 

• Saccharomyces cerevisiae got its name, because it was first observed in yeast cells, which were commonly used for fermentation. The name was assigned by Theodor Schwann in 1837. The word Saccharomyces comes from the Latin words "saccharo" meaning “sugar”, and "myce" which means “fungus”. Yeast is a single-celled fungus that converts sugars into alcohol through the process of alcoholic fermentation. The word "cerevisiae" is derived from the Latin word "cerevisia", which means “beer”. 

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​     Even though it is common to see the scientific names written in many different formats, there are actually only a couple of acceptable formats in which they should be written. The genus should be capitalized and italicized, whereas the epithet name is not capitalized but is also italicized. The genus name can either be written out fully, as in Escherichia coli, or it may be abbreviated, as in E. coli.  Alternatively, the scientific name may be underlined instead of italicized. For example, Escherichia coli and E. coli, are also acceptable formats.