Structure and economic importance of Bacteria.

Systematic position

     Thallophyta

          Schizophyla

                Schizomycetes

                       Eubacteriales

                                  Bacteria

It was Von Leeuwenhock,who discovered bacteria in 1675 and studied it under a simple microscope developed by himself. He named that micro-organisms as 'Animacule'. Ehrenberg C.G. in 1828 named it as 'Becteria'. Louis Pasteur in 1864 gave first description of Bacteria.He made detailed study of this microorganism and established a new branch 'Bacteriology'.

 The modern description of ultrastructure of a bacterial cell could only be possible after the discovery of electron microscope. The study under the electron microscope provide the detailed structure of a bacterial cell .A brief description is given here on the basis of electron microscopic study.

Structure

The structure of a bacterial cell may be basically divided into three main parts (a) cell wall (b)cytoplasm and (c) nuclear material

A.Cell-wall:-

              The cell wall of a bacterial cell consists of three layers (a)slime layer- the— outermost layer (b) cell- wall —middle layer (c) cytoplasmic membrane— the innermost layer.

(a) Slime layer- It is the outermost layer of the cell made up of gummy and mucilagenous substances. This layer is sometimes thick and forms the shape of the cell more or less like a capsule .so the Bacterial cell is also called capsule .

 Being the outermost layer  it functions as protective and preventive layer.

(b) Cell -wall -It is the second layer of the cell wall just inside the slime layer forming middle layer. It is true cell wall which is rigid, elastic and mainly protective in function.

(c) Cytoplasmic membrane—It is  the innermost layer of the cell wall laying inside the middle layer. It is actually the protein layer of cytoplasm being thicker and denser in nature. It is provided with sufficient quantity of lipids and lipoproteins. It surrounds the cytoplasm of the cell and functions as permeable membrane.

B.Cytoplasm:-

The cytoplasm is spread all over the space homogeneously inside the cell-wall. In the younger stage of cytoplasm is provided with several tiny dense particles of ribosome.Ribosome is chemically made of of RNA and protein . The ribosomal particles are distributed uniformly in cytoplasm . The outer structure found in cytoplasm are known as cell inclusions. The main cell inclusions are —

(a) Metachromatic granules:—These granules may be observed by treating with methylene blue. The granules maybe found throughout the cytoplasm or or at the ends of the cell in groups .It is mainly  nitrogenous reserved food substances. Sometime these granules are also referred as volutine granules.

(b) Fats(lipid droplets):—The fat droplets are also reserved food materials. Usually formed in nitrogen fixing soil bacteria (Azotobacter or  Rhizobium) or in spirillum.

(c) Mesosome:—The Mesosome is a membranous structure of cytoplasm and arise a invagination of plasma membrane. The Mesosome is active in Cell-wall synthesis and secretion of extra cellular substances.

C.Nuclear material:

The true nucleus is absent in bacterial cell and hence bacteria come to the prokaryotes. The recent studies reveal that a primitive or incipient nucleus is present in centre as chromatin granules .The chromatin granules functions as nucleus and are present in definite numbers during the period of active growth .The granules are chemically deoxyribose nucleic acid (DNA), find in centre as bundles of fibres. The bacterial nucleus is never surrounded by a nuclear membrane and does not take part in mitosis or other type of cell division .The nucleus only divides just before the division of whole bacterial cell.

             Economic importance

.. The plants and animals including human being are greatly concerned with the activities of bacteria .There is not even a single organised on the earth which is unaffected from bacteria. Bacteria are microbes and found everywhere in all types of environment. They remain alive in all range of temperatures and on all heights of Earth. They have control over all the activities of plants and animals. So bacteria are our nearest friend as they have countless activities which are useful for us .At the same time there are a large number of activities which are very harmful to us. Considering these harmful activities the bacteria prove themselves as our great enemy. Therefore that is a proverb that bacteria are our friend and foe

A. Beneficial activities of bacteria

1. Sanitation

           Sanitation is the most essential requirement of life and that is done by bacteria to a great extent .The bacteria have a property of decomposition. Due to this property the bacteria act on cow dung, human excreta ,sewage products, industrial waste, dead bodies and all other waste matter and decomposes them into simple organic compound which come to the soil and become available to the plants and animals.

2. Soil fertility

        

            Man and animals depend on soil for their food. Not only these, the plants also depend on soil for their food. The production of food grains, vegetables, pulses ,fruits etc entirely depend on the fertility of soil ,and the fertility  is dependent on the activities of bacteria. The bacteria present in soil and in root nodules of leguminous plants take nitrogen from atmosphere and fix it in the soil after several changes in the form of nitrate. This nitrate increases the fertility of soil. The bacteria also decomposes that dead bodies and their part into small organic compounds which ultimately come to the soil to increase the fertility.

3. The industrial activities

        ★Fermentation:- The anaerobic decomposition of sugars, carbohydrates, and starches by the enzymatic action of bacteria is known as fermentation. Fermentation has a very important place in the field of industry because all type of alcohols, beers ,wines, cheese, bread and different type of organic  acids are produced by the process of fermentation on industrial scale.

e.g-production of alcohols, preparation of acetic acid (vinegar), Lactic acid ,amino acid ,butaric acid.

★Retting of jute:-the the jute fibres are obtained after retting of jute. It is is done on large scale by defeating the stem cutting of jute in water.

The  clostridium bacteria present in water act upon them decomposes them and separate the fibres.

★Curling of tobacco leaves:- The tobacco leaves are  curled, improved to colour, texture and aroma by the process of fermentation by Bacillus megatherium , Bacillus sarbatilis bacteria

★Curding of milk:-The streptococcus lactis bacteria act upon milk and ferment it into curd.

★Baking industry:-The breads are  obtained from the process of  fermentation by Saccharomyces cerecisiae bacteria.

★Production of vitamins and enzymes:-Many vitamins and enzymes are produced with the help of bacteria. Vitamin B12 is obtained by streptomyces bacteria 

.

4. Medicinal value

★Medicine production:-a large number of medicines are obtained by the activity of bacteria .

example-

Name of bacteria.         Name of medicines

★Streptomyces griseus                Streptomycin

★Bacillus brevis                                    Thyrothrycin

★Streptomyces venezuele                  Chloromycetin

★Vaccines:-Many vaccines are  obtained by the activities of different type of bacteria , such as vaccine for T.B ,Smallpox, Diphtheria, Cholera, Influenza, Polio and Tetanus  etc.

B.The harmful activities of bacteria

1.Diseases:-Almost all dreadful disease are caused by either bacteria or       virus.

Pneumonia, Influenza, Typhoid, Cholera, Diphtheria, Dysentery,T.B are caused by bacteria whereas Cancer is caused by Virus.

★Diseases produced by bacteria in Man:-

Name of bacteria               Name of disease

→Bacillus typhosus                      Typhoid

→Clostridium tetani                     Tetanus

→Vibro Cholera                             Cholera

→Corynbacterium diphtherae     Diphtheria

→Hemophilous Influenzae          Influenza

→Mycobacterium tuberculosis   T.B.

★ Disease produced by bacteria in plants

 Name of bacteria                                   Name of disease

→Xanthomonas                                            Citrus canker

→Corynbacterium repondonicum 

2.Food poisoning:-Food poisoning is mainly caused by bacteria .The food ,fruits, vegetables are spoiled by bacteria.

3.Denitrification:-The fertility of soil is  decreased  due to denitrification which is caused by Bacillus denitrificans bacteria