Classification of Bacteria part 1

Classification of Bacteria
Classification, nomenclature, and identification are the three separate but interrelated areas of taxonomy. Classification can be defined as the arrangement of organisms into taxonomic groups (taxa) on the basis of similarities or relationships. Classification of prokaryotic organisms such as bacteria requires a knowledge obtained by experimental as well as observational techniques, because biochemical, physiologic, genetic, and morphologic properties are often necessary for an adequate description of a taxon .Nomenclature is naming an organism by international rules according to its characteristics. Identification refers to the practical use of a classification scheme: (1) to isolate and distinguish desirable organisms from undesirable ones; (2) to verify the special properties of a culture in a clinical setting, (3) to isolate and identify the causative agent of a disease.
Criteria for Classification of Bacteria
The valuable information can be obtained microscopically by observing cell shape and the presence or absence of specialized structures such as spores or flagella. Staining procedures such as the Gram stain can provide reliable assessment of the nature of cell surfaces. Some bacteria produce characteristic pigments, and others can be differentiated on the basis of their complement of extracellular enzymes; the activity of these proteins often can be detected as zones of clearing surrounding colonies grown in the presence of insoluble substrates (eg, zones of hemolysis in agar medium containing red blood cells).

Identification & Classification Systems
1-Numerical Taxonomy
Numerical taxonomy (also called computer taxonomy, phenetics, or taxometrics) became widely used in the 1960s. Numerical classification schemes use a large number (frequently 100 or more) of unweighted taxonomically useful characteristics.

2-Phylogenetic Classifications:
Toward an Understanding of Evolutionary Relationships among Bacteria Phylogenetic classifications are measures of the genetic divergence of different phyla (biologic divisions). Close phylogenetic relatedness of two organisms implies that they share a recent ancestor, The genetic properties of bacteria may allow some genes to be exchanged among distantly related organisms. Furthermore, multiplication of bacteria is almost entirely vegetative, and their mechanisms of genetic exchange rarely involve recombination among large portions of their genomes The formal ranks used in the taxonomy of bacteria are listed in Table 1.


Table 1. Taxonomic Ranks.



Formal Rank Example
Kingdom Prokaryotae
Division Gracilicutes
Class Scotobacteria
Order Eubacteriales
Family Enterobacteriaceae
Genus Escherichia 
Species coli 


3-Bergey s Manual of Systematic Bacteriology
Bergey s Manual of Systematic Bacteriology. First published in 1923, the Manual is an effort to classify known bacteria and to make this information accessible in the form of a key. A companion volume, Bergey s Manual of Determinative Bacteriology, serves as an aid in the identification of those bacteria that have been described and cultured.
Description of the Major Categories & Groups of Bacteria
There are two different groups of prokaryotic organisms: eubacteria and archaebacteria. Eubacteria contain the more common bacteria, ie, those with which most people are familiar. Archaebacteria do not produce peptidoglycan, a major difference between them and typical eubacteria. They also differ from eubacteria in that they live in extreme environments (eg, high temperature, high salt, or low pH) and carry out unusual metabolic reactions, such as the formation of methane. A key to the four major categories of bacteria and the groups of bacteria comprising these categories is presented in Table 2. The four major categories are based on the character of the cell wall: gram-negative eubacteria that have cell walls, gram-positive eubacteria that have cell walls, eubacteria lacking cell walls, and the archaebacteria.










Table 2. Major Categories and Groups of Bacteria That Cause Disease in Humans Used As an Identification Scheme in Bergey s Manual of Determinative Bacteriology, 9th Ed.



I. Gram-negative eubacteria that have cell walls  
   Group 1: The spirochetes Treponema
Borrelia
Leptospira
Campylobacter
Helicobacter
Spirillum
None
  Group 4: Gram-negative aerobic/microaerophilic rods and cocci Alcaligenes
Bordetella
Brucella
Francisella
Legionella
Moraxella
Neisseria
Pseudomonas
Rochalimaea
Bacteroides (some species)
Escherichia (and related coliform bacteria)
Klebsiella
Proteus
Providencia
Salmonella
Shigella
Yersinia
Vibrio
Haemophilus
Pasteurella
Bacteroides
Fusobacterium
Prevotella
None
  Group 8: Anaerobic gram-negative cocci None
  Group 9: The rickettsiae and chlamydiae Rickettsia
Coxiella
Chlamydia
None
  Group 11: Oxygenic phototrophic bacteria None
  Group 12: Aerobic chemolithotrophic bacteria and assorted organisms None
  Group 13: Budding or appendaged bacteria None
  Group 14: Sheathed bacteria None
  Group 15: Nonphotosynthetic, nonfruiting gliding bacteria Capnocytophaga
  Group 16: Fruiting gliding bacteria: the myxobacteria None
II. Gram-positive bacteria that have cell walls  
  Group 17: Gram-positive cocci Enterococcus
Peptostreptococcus
Staphylococcus
Streptococcus
Bacillus
Clostridium
Erysepelothrix
Listeria
Actinomyces
Corynebacterium
Mobiluncus
Mycobacterium
  Groups 22–29: Actinomycetes Nocardia
Streptomyces
Rhodococcus
 
   Group 30: Mycoplasmas Mycoplasma
Ureaplasma
 
  Group 31: The methanogens None
  Group 32: Archaeal sulfate reducers None
  Group 33: Extremely halophilic archaebacteria None
  Group 34: Cell wall-less archaebacteria None
  Group 35: Extremely thermophilic and hyperthermophilic sulfur metabolizers None