Classification and Nomenclature

I. All living organisms are classified into a system originated in 1735 by Carl von Linne (von Linne changed his name to Carolus Linnaeus because it sounded more Latin and thus fit in with his classification system better). This scheme includes the following seven levels:

Kingdom

Phylum or Division

Class

Order

Family

Genus

Specific epithet

A. most of our discussions will involve organisms referred to by a two-part scientific name (binomial nomenclature). This name consists of the genus and specific epithet. The genus is capitalized while the specific epithet name is not. Both are italicized (ex. Bacillus cereus) or underlined (Bacillus cereus).

1. In your reading, after an organism has been referred to once, its genus name will be abbreviated to a single letter (ex. Bacillus cereus becomes B. cereus).
2. A third name will sometimes be given. This is referred to as the subspecies or strain name. Usually strains of the same species differ in only minor and extremely subtle ways.  

B. The most inclusive grouping in the classification of living organisms is the Kingdom. The most widely used scheme of classification is the five-kingdom system proposed by Robert Whittaker in 1969. The kingdoms we will be concentrating on most in this class are: Monera (or Prokaryotae), Protista and Fungi (or Myceteae). We will pay passing attention to Animalia.

1. All members of the kingdom Monera are prokaryotic organisms known as bacteria. These organisms are classified according to biochemical capabilities and visible characteristics. Characteristics used for classification and, subsequently, identification will be discussed shortly.

a. The cells of prokaryotic organisms are smaller and lack the internal compartments (organelles) of eukaryotic cells.
b. Prokaryotic cells never form multicellular organisms. They will congregate into colonies or multicellular arrangements (such as long strings of bacteria attached end to end) but never form tissues or organs seen in animals or plants.

c. Recently it has become apparent that two radically different types of bacteria exist.  Living in extreme environments (high temperature, high salt, etc.) are a type of bacteria that are now referred to as Archaea. These bacteria have significant biochemical differences from the run-of-the-mill bacteria found in less extreme environments (eubacteria).  For the most part when we talk of prokaryotic organisms in this class we will be referring to eubacteria.

2. Members of the kingdom Fungi are eukaryotic; their cells have organelles and are larger than the cells of bacteria. These species can exists as unicellular or multicellular organisms. Fungi are saprophytic. They must absorb nutrients from their environment. Included in this kingdom are the molds, mushrooms and yeasts.
3. Members of the kingdom Protista are eukaryotic and most are capable of movement. Some types of algae are included in this family. Algae are capable of photosynthesis; consequently, they are less reliant on absorption or ingestion of nutrients from the environment. Members of protista are capable of both sexual and asexual reproduction but do not develop from embryos (like plants and animals) or produce spores (like fungi). 
4. Members of the kingdom Animalia consist of eukaryotic cells and are multicelluar. There cells lack cell walls. At some stage in there development, animals are capable of movement.  They reproduce primarily via sexual reproduction and develop from an embryo.  The only animal species we will address directly will be the parasitic worms, the helminthes. Indirectly we will address more complex animals that act as vectors for disease.

5. Members of the kingdom Plantae are multicellular, eukaryotic and are capalbe of photosynthesis.  They are capable of both sexual and asexual reproduction.  

C. Viruses are different! Though sometimes mistakenly included in the kingdom Monera, viruses consist of nucleic acids, proteins and usually a little lipid. They have no capacity of their own to carry out those biochemical reactions necessary for life. Instead they invade and take over cells (either eukaryotic or prokaryotic). They then reproduce by using the biochemical systems of that cell for their own designs.

1. Viruses are extremely specific about both the species they will infect and which cells within the organism they can reproduce in.
2. Viruses that infect bacteria are referred to as phages. Phages are also specific about the species they will attack and utilize for reproduction. For example, the phage that will infect cells of the species Escherichia coli usually will not infect cells of the species Bacillus cereus.  In some cases, phages are specific for certain subspecies, not infecting other cells of the same species but different subspecies. Differences in susceptibility to phage infection is sometimes used to identify certain subspecies.

Some links!!

Classification, Nomenclature, Laboratory Identification   University of Texas Medical School

http://medic.med.uth.tmc.edu/path/00001458.htm

 

Principles of Classification of Eubacteria   Prescott, Harley and Klein (1998) Microbiology

http://www2.ntu.ac.uk/life/sh/modules/hlx202/Lectures/Lectured.htm