Sunday, 20 May 2012

Structure Of Bacteria


Bacteria when observed under the electron microscope, shows detail cell structure.
The bacteria has a nucleus without a nuclear membrane.
Based on the staining technique of Christian Gram the bacteria are classified into two types.
  1. Gram positive.
  2. Gram negative.
Bacteria shows the following structures.

Cell Wall
  • The bacterial cell is enclosed by a definite and complex cell wall.
  • The cell composes of several peptidoglycan or mucopeptide layers.
  • The cell wall of gram positive bacteria contains teichoic acid. In gram negative bacteria it is absent.
Functions Of Cell Wall
  1. It gives definite shape and size to the cell.
  2. It protects the cell from toxic materials.
  3. It protects the cell from osmotic lysis.
  4. In some bacteria the components of the cell wall lead to its pathogenic nature.

Gram Positive

A gram positive bacteria is almost similar to gram negative bacteria internally. but, it is totally different in its structure externally. It has cytoplasmic lipid membrane. It has a thick peptidoglycan layer which is made up of mucopeptides, glycopeptides, mureins and which constitutes about 95% of the total cell wall. Teichoic acids and lipoids are present which link to form  lipoteichoic acids. These lipoteichoic acids act as chelating agents and help in attachment to certain substances. The function of teichoic acids is not completely known yet.

Gram Negative

It has a cytoplasmic membrane. It has a thin peptidoglycan layer compared to gram positive bacteria. Outer membrane consists of Lipopolysaccharides. There is a space between the layers of peptidoglycan and the secondary cell membrane called the periplasmic space.

Structures Outside the Cell Wall
The structures present outside the cell wall help in protection, attachment to other objects and movement of the cell.

  • It is a sugar coat formed by the network of polysaccharides.
  • It is present just outside the cell wall.
  • It is also known as the bacterial capsule.
  • It protects the bacteria from phagocytes.


  • It is 20nm in its thickness.
  • It is made up of a protein called flagellin.
  • It is hollow, cylindrical and helical in shape.
  • The flagellin is responsible for the helical structure of the flagella.
  • It helps in locomotion.


  • It is a thin, hollow, cylindrical, hairlike structure.
  • It is similar to flagella.
  • It does not promote locomotion.
  • It is helps in attachment to surfaces.
  • Some pilli called as sex pilli help in the transfer of genetic material.

Tuesday, 21 February 2012

What Are Bacteria?

  • Bacteria are unicellular micro-organisms. These are Prokaryotic in cellular organisation and placed under the kingdom Monera in a single Class Schizomycetes.
  • Bacteria were not known until the invention of the microscope.
  • Bacteria were discovered by Anton van Leeuwenhoek in Delft, Holland in 1676.
  • Leeuwenhoek with the help high power lenses observed his own teeth scrapping and found that it contained millions of living creatures or organisms and he named them Animalcules.
  • Ehrenberg first called these creatures as Bacteria.
  • Later researches were carried out by Louis Pasteur and Robert Koch which highlighted the importance of bacteria.
  • But at present a lot of information is available regarding bacteria and viruses.
Characters of Bacteria
  • Bacteria are found in soil, water, air and also inside the body of living organisms.
  • These can withstand extreme drought, cold and heat.
  • Some bacteria live as parasites on other living organisms and plants.
  • Some plants live in symbiotic association. For example., Rhizobium forms root nodules of legumes and fixes atmospheric nitrogen, Escherichia coli commonly called E.coli lives in the intestine of man.
  • Bacteria are found in different shapes such as rod shape, spherical shape, comma shape, and spiral shape.
  • Bacteria that change their shape according to the environment and nutrients available are called pleomorphic bacteria. For example., Acetobacter.

Sunday, 12 February 2012


  • Microbiology is a branch of biology that deals with the study of invisible organisms or micro-organisms. These organisms can be observed in the microscope only.
  • Organisms such as algae, fungi, protozoa, bacteria, viruses fit into this criteria and hence are referred as micro-organisms. However some algae and fungi are macroscopic and visible with naked, yet they are studied my microbiologists.
  • Microbiology employs techniques such as sterilization and the use of culture media that are necessary for successful isolation and growth of micro-organisms.
  • Micro-organisms are present everywhere in our environment.
  • There are some micro-organisms that can tolerate extreme acidic, alkaline conditions, high and low temperatures and salt concentrations. Such organisms are called acidophilic, alkalophilic, thermophilic and halophilic organisms respectively.
Importance of Microbiology
  • Micro-organisms recycle elements such as oxygen, sulphur, carbon, nitrogen, phosphorus.
  • Micro-organisms help in creating a disease free world by producing antibiotics and vaccines.
  • The antibiotic Penicillin was discovered by Alexander Fleming from a fungus called Penicillium notatum.
  •  Walksman obtained Streptomycin from Streptomyces griseus.
  • Industrial products such as enzymes, amino acids, vitamins, organic acids and alcohols are commercially produced by micro-organisms.
  • Micro-organisms play an important role in production of dairy products.
  • Microbes like bacteria and fungi are used in sewage disposal.
  • Micro-organisms are also used in extracting valuable metals such as uranium from the rocks. This reduces more than 20% of the cost.
  • One of the biggest achievements of microbiology is the ability to alter genetic material of organisms. This is commonly referred to as Genetic Engineering.
  • Micro-organisms are used as bio-control agents.
  • Methane gas is also produced by the activity of  micro-organisms, which can be used as a fuel.
With the advent of RDNA technology and genetic engineering microbiology has become a weapon to unravel the challenges in the field of Biotechnology.