Systematic Classification of Bacteria, Biology tutorial


The most commonly employed reference for bacteria categorization is Bergey's Manual of Systematic Bacteriology, which is categorized into four volumes. Divisions in Bergey's manual are based on features like: Gram, reaction, cell, cell arrangement, shape, oxygen necessity, motility and metabolic properties.

Bacteria are as well categorized according to the international agreed rules through the international committee on methodical bacteriology.

Bergey's Manual of Systematic Bacteriology - Volume 1:

Ordinary Gram Negative Bacteria:

Bergey's Manual of Systematic Bacteriology, Volume 1 is build up of the ordinary Gram negative chemo heterotrophic bacteria, most of which have clinical, industrial and agricultural significance. They comprise:

The Spirochetes:

These bacteria encompass helical shapes. They encompass the capability to twist and contract their shape (that is, they are flexible). There is a presence of a special type of flagella known as periplasmic flagella or axial fibrils which might be more than one. They are so thin they can't be simply seen in light microscope. If gram stained, dark field microscope is employed to visualize such organisms, they are Gram negative bacteria. Most of the spirochetes are human pathogens.

Aerobic/motile, Helical/Vibrioid Bacteria:

They are Gram negative bacteria. The cells are rigid and range from vibrioid (that is, having less than one tumor twist) to helical. They swim by means of the polar flagella.

They are aerobic or microaerophilic. Most of them are harmless saprobes and take place in soil, fresh water or marine atmosphere however a few are parasitic and pathogenic for human animals and other bacteria. 

Non Motile Gram Negative Curved Bacteria:

These bacteria contain rigid cell which are curved to a variety of degrees forming coil, helical spirals and at time ring, they are not motile. They take place mostly in soil, fresh-water and marine atmosphere.

Gram Negative, Aerobic Rods and Cocci:

This group of bacteria makes one of the biggest and most diverse groups of bacteria. They are straight or slightly curved rods, a few of them are cocci. They are a severely respiratory kind of metabolism: 

Most of industrially, medical and environmentally significant bacteria habitats comprise water, soil and animal parasites.

Facultatively Anaerobic, Gram-Negative Rods:

Most of the important pathogens, oxidase and a need for organic habitats comprise plants, soil and animals, respiratory and intestinal regions. Most of this in the group is termed as 'enteric' found in the human intestine.

Aerobic, Gram-Negative Rods:

They are straight, curved and helical rods. They are rigid. They are obligately anaerobic (that is, can't live in pressure of O2), mainly found in the intestinal traits, some in mouth and genital trait and some of the most general organism in the intestine.

Dissimilatory Sulphate-Reducing or sulphur-Reducing Bacteria:

They contain a Gram-negative cell wall. They are mainly found in anaerobic sediments; decrease oxidized forms of sulphur to H2S. Dissimilation = nutrition not assimilated however instead excreted, take place in mud, fresh-water, marine and brackish environments.

Bergey's Manual of Systematic Bacteriology - Volume 2:

Ordinary Gram-Positive Bacteria:

Bergey's Manual of Systematic Bacteriology - Volume 2 is build up of the ordinary gram positive chemo heterotrophic bacteria, most of which encompass industrial, clinical or agricultural significance. They are:

a) Gram-Positive Cocci. Aerobic/Facultatively Anaerobic Cocci:

- They have cytochrome.

- They are capable to respire by means of oxygen.

- A few of them can as well get energy beneath anaerobic conditions through fermentation.

- Members are positioned in two families: Deinococcaceae and Micrococcaceae.

b) Aerotolerant Fermentative Cocci:

- They don't have cytochromes.

- They have merely a fermentative kind of metabolism and don't respire yet they can grow aerobically and anaerobically.

- The cells are arranged in chains, pairs or tetrads.

- Some representative genera comprise Streptococcus, Leuconostoc and Pediococcus.

c) Anaerobic Gram-Positive Cocci:

These cocci contain a fermentative kind of metabolism, cells in tetrads, clusters, short or long chains.

Endospore Forming Gram-Positive Bacteria:

  • Most of them are rod shaped however some are cocci.
  • Majority of them are gram-positive however some species stain gram-negative.
  • Motility when present is by means of peritrichous flagella.

Anaerobic Spore forming Rods:

They encompass a fermentative kind of metabolism. They are broadly distributed in soil, in marine and fresh water anaerobic sediments. They comprise Desulfotomaculum and Clostridium.

Non-Spore making Gram Positive Rods of regular shape:  

  • They are long or short rods in shape.
  • The group is build up of harmless saprobes.
  • A few of them are parasitic organisms.

Non-Spore making Gram-Positive of Irregular Shape:

This group comprises of a heterogeneous diversity of bacteria. Some of the general features are as follows:

a) Might be aerobic or facultatively anaerobic.

b) Aerobic/Facultatively Anaerobic branched Filamentous Rods. The bacteria of such group form colonies that at first are microscopic in size (that is, micro colonies) and have branched filamentous cells. As the colonies build up to macroscopic size most of the cells become diphtheroid (such as caryobacteria) or cocci in shape. Illustrations comprise Arachnia and Agromyces.

c) Anaerobic Non-filamentous or Filamentous. The organisms are either anaerobes or when facultatively anaerobic are preferentially anaerobic. Two of the genera in this group are Actinomyces and Propionbacterium. They are distinguished by their morphology and by their fermentation end products as determined through gas chromatography.


They belong to aerobic bacteria. Their cell walls comprise high amounts of lipids. They are building up of a single genus Mycobacterium that is slightly curved or straight rods which might show branching. They are acid fast.


They are aerobic bacteria which produce a substrate mycelium that is, a mat of branching hyphae formed beneath the surface of the agar medium.

Bergey's Manual of Systematic Bacteriology - Volume 3:

The organisms in this volume encompass unusual properties that are quite dissimilar from those in volumes one and two. The anoxygenic Phototrophs can be splitted into two main groups based on their pigmentation purple bacteria and green bacteria. They take place in anaerobic fresh water or marine atmosphere. They can as well take place below the surface of shallow aquatic atmospheres rich in organic matter like stagnant ponds and ditches.

Anoxygenic Phototropic Bacteria:

They mainly belong to the order Rhodospirillales. They are Gram-negative and able of carrying out photoorganotrophic and photolithothrophic kind of metabolism.

They contain bacteriochlorophyll. As well present in their cells are different water-insoluble carotenoid pigments which can as well trap or absorb light energy and broadcast it to the bacteriochlorophyll. 

The anoxygenic bacteria grow phototrophically only in anaerobic conditions and are not capable of forming O2 as they possess simply photosystem.

Oxygenic Phototrophic Bacteria:

They are bacteria that contain chlorophyll. They can employ light as an energy source and develop O2 in a manner identical to that of green plants. The group comprise: the Cyanobacteria (that is, blue-green algae).

Gliding, Fruiting Bacteria:

  • Gram-negative, non-phototrophic bacteria 
  • They be deficient in flagella; yet can glide across the solid surfaces.
  • They encompass a complex life-cycle in which the cells swarm altogether in masses and form fruiting bodies.
  • The fruiting bodies have myxo-spores that are shorter and thicker than the vegetative cells.
  • They are mainly found in the surface layers of soil, manure, compost, rotting wood and animal dung. Constituent genera comprise Stigmatella Chondromyes.
  • They are aerobic and microaerophilic organisms.
  • They live in soil or water.

Gliding, Non-fruiting Bacteria

Gram-negative non-phototrophic rods, filaments or multicellular trichomes which glide across solid surfaces: fruiting bodies are not generated. 

Illustrations of organisms comprise Cytophaga, Flexibacter, Simonsiella, Vitreoscilla Beggiotoa, Saprospira and Thiothrix.


Gram-positive or Gram-negative which are phylogenetically distinct from eubacteria; some generate methane gas; some need unusually high level of NaCl for growth: others are differentiated by their capability to grow at a low pH and a high temperature. Three major categories of Archaeobacteria acknowledged are the methanogens the red extreme halophiles, and the thermo-acidophiles.

Bergey's Manual of Systematic Bacteriology - Volume 4:

Gram-positive filamentous bacteria of the complex morphology:

The organisms in volume IV are the aerobic gram positive bacteria that form structures like mycelium of filamentous hyphae and asexual spores as found in microscopic eukaryotic fungi and encompass different cell kinds of cell walls based on the amino acid and sugar composition.

Filamentous bacteria which split in more than one plane:

The hyphae split not only transversely however as well longitudinally to generate cluster or packet of cells or spore; cell-wall type iii; soil organisms, animal pathogens and symbiotic nitrogen-fixers are represented. The genera represented in this group are: Geodermatophilus, Dermatophilus and Frankia.

Filamentous bacteria which form true sporangia:

Nontoxic soil and water organism whose hyphae split in a single plane; the spores are made in special sacs; cell-wall type ii or iii. A good illustration of a genus in this division is Actinoplanes.

Streptomyces and correlated genera:

The hyphae split in a single plane; long chain of conidiophores is made at the tips of sporogenic hyphae; the organism is mostly harmless soil organism which are noted for production of antibiotics; some are plant or human pathogen; cell-wall type.

Some of the genera in this group comprise Actinopycnidium, Streptroverticullium, Actinosporangium however the most popular of such genera is the Streptomyces.

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