Introduction to Prokaryotes

The prokaryotes are an organization composed of millions of genetically different unicellular microorganism. They have a low structural diversity, however are genetically and physiologically very diverse (Kenneth Todar, 2009). Particular qualities help to assemble or recognize, particular band of prokaryotic organisms to microbiologists. The classification design is dominated by the prokaryotes phylogeny. Inside the phylogenic Tree of Life, prokaryotes are split into 2 domains
  • Archaea
  • Bacteria
The new model of Bergey's Manual of Systematic Bacteriology, exposed the life of 24 different phyla of bacteria. Extant phyla of the Site Bacteria
  1. Acidobacteria
  2. Actinobacteria
  3. Aquificae
  4. Bacteroidetes
  5. Chlamydiae
  6. Chlorobi
  7. Chloroflexi
  8. Chrysiogenetes
  9. Cyanobacteria
  10. Deferribacteres
  11. Deinococcus-Thermus
  12. Dictyoglomi
  13. Fibrobacteres
  14. Firmicutes
  15. Fusobacteria
  16. Gemmatimonadetes
  17. Nitrospirae
  18. Planctomycetes
  19. Proteobacteria
  20. Spirochaetes
  21. Thermodesulfobacteria
  22. Thermomicrobia
  23. Thermotogae
  24. Verrucomicrobia

What are bacteria?

Bacteria are unicellular organisms and almost all of them multiply by binary fission. Water bodies, land and air are teeming with these microscopic microorganisms known bacteria. Many of them are free-living microorganisms; however some of them need dog or herb hosts to complete their live routine. Scientifically bacteria are the most abundant living things on earth. Bacterial study also called as, Bacteriology, revealed these microscopic microorganisms are intricately associated with every life process, whether that of human animal or plant life. Bacteria absorb nutrients from their bordering environment secret a mixture of waste that help their development and success and excrete waste products.

Structure, Size and Shape of bacteria

Each bacterium is an individual cell, which is very minuscule, in regards to a few micrometers (10-6 meters) in length and has a very simple framework. A bacterium cell has five important structural constituents, a cell wall, a cell membrane, a nucleoid (DNA), ribosomes and some sort of surface level which can or can not be built in the wall. Based on the framework, there are three distinctive parts of the cell. Starting with appendages that are attached to the top of cell in form of flagella or pili, a cell envelop, constituting of any capsule, a cell wall structure and a plasma membrane and lastly the cytoplasmic region which has the skin cells organelles.

Table 2. 1: Brief summary of functions and characteristics of typical bacterial cell structures



Predominant substance composition(s)


Swimming motion.



Sex pilus

Stabilizes mating bacteria during DNA transfer by conjugation.


Common pili or fimbriae

Attach to surfaces; protects against phagocytic engulfment.


Capsules (includes "slime tiers" and glycocalyx)

Attach to floors; protects against phagotrophic engulfment, sometimes get rid of or digest; storage space of nutrition or protects against dehydration.

Usually polysaccharide; almost never polypeptide

Cell wall

Gram-positive bacteria

Prevents from osmotic break down of cell protoplast and add rigidity and condition to cells.

Peptidoglycan (murein) complexed with teichoic acids

Gram-negative bacteria

Peptidoglycan inhibits osmotic breakdown and present rigidity and condition; permeability of outer membrane act as a barrier; merged LPS and protein have a number of functions.

Peptidoglycan (murein) enclosed by phospholipid protein-lipopolysaccharide "outer membrane"

Plasma membrane

Transportation of solutes, permeability barrier; ATP technology; site of various enzyme systems.

Phospholipid and protein


Sites of translation (health proteins synthesis)

RNA and protein


Often reserves of nutrients; additional specialised functions

Highly varying; carbohydrate, lipid, protein or inorganic


Genetic materials of cell


[source: Kenneth Todar, 2009]

Various bacterias can be identified, simply through aesthetic perusal. The identification begin by considering the appearance of the bacterial colony, accompanied by viewing specific bacterium under a microscope and considering the patterns, types of groupings and other feature including the location and volume of flagella. Regarding to designs and cell plans, there are three main morphological categories of bacteria, cocci (spherical), bacilli (rod-shaped) and spiral (twisted) however pleomorphic bacteria can have various shapes. Cell organisation can be singularly, in clusters and in chains.

Cocci may be oval, elongated, or flattened on one part and can remain fastened after cell section.

Figure 2. 1: Preparations of cocci; [source: Anon]

Bacillus is a fishing rod shape. As bacilli separate only across their short axis there are fewer groupings.

Figure 2. 2: Plans of bacilli; [source: Anon]

Spiral bacteria have one or more twists.

Figure 2. 3: Plans of Spiral bacteria; [source: Anon]

Nutritional classification for bacteria

Bacteria have various requirements for progress. As bacterias are greatly influenced by environmental conditions, their growth depends upon the support with their environmental niches for his or her individual needs. The main environmental factors influencing microbial growth are pH, normal water activity, oxygen levels and temp; however the option of nutrition in their surroundings is also a key point (Micheal H. Geradi, 2006). The major dietary types of bacterias are (Anon)

  • Photoautotrophs are microorganisms that can convert light energy into chemical substance energy.
  • Photoheterotrophs are organisms that make organic carbon as a source for biosynthesis however use light energy to create ATP (photosynthesis).
  • Chemoautotrophs or Lithoautotrophs (Lithotrophs) are microbes that obtain their energy by oxidizing inorganic ingredients such as iron, hydrogen gas and hydrogen sulfide.
  • Chemoheterotrophs or Heterotrophs are bacteria that derive their way to obtain energy from organic materials such as sugars, lipids and proteins.

Microbial classification matching to environmental requirement of growth.

Physical and chemical type conditions of the surroundings greatly affect the actions of microorganisms. Different organisms react differently the many kinds of environmental conditions. A host which is favourable to one microorganism may be damaging another; however some microbes are suffering from tolerance to undesirable condition in which they cannot development properly. Organisms may respond in a different way to a habitat in term of, success, growth, differentiation and duplication (E. B. Smith). The major factors impacting on microbial development are
  • Temperature
  • Oxygen
  • pH
  • Water activity (Osmotic effects)


Temperature probably is the main factor affecting development, because if heat changes happen microorganisms will stop growing. The average temps for bacterial progress vary among microorganisms. Some varieties of microbes can expand at low temperature as -10oC among others at high temperature as 100oC or even higher (John Blamire, 2000). The bigger and lower heat affect the cell metabolism. At low temperatures, debris move slower, enzymes cannot control chemical substance reactions, and therefore the viscosity of the cytoplasm brings all activity to a halt. An increase in temps make particles to go faster, metabolism is improve up by enzymes activities and progress rate increases. However cellular expansion ceases as temperature increases to a spot where enzymes denaturation occurs anticipated to raised rate of activities (John Blamire, 2000). Each microorganism has

  • a minimum temp for development and below which development will minimize,
  • an optimal temps which allow swift growth,
  • and a maximum heat range and above which the development is impossible.

These three types of temperature are called cardinal temps and are unique to each type of microorganisms.

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