Monera : Monera is the most plentiful and smallest living organisms on the earth. These are found everywhere on land. They can be found in hot springs, underside ice bags and on the deep ocean floor, in the hottest and driest deserts as parasites on and in other life forms.
Characteristics of Monera
1. These are Prokaryotic Unicellular organisms.
2. Does not have a well-defined nucleus or any membrane bound organelle.
3. Monera have a rigid cell wall.
4. There are various modes of nutrition. Could be autotrophs or heterotrophs.
5. They behave as decomposers and mineralisers in the biosphere.
Classification of Kingdom Monera
Eubacteria Archaebacteria
(True bacteria) (Ancient bacteria)Other subgroups of Cyanobacteria
of bacteria (Blue-green algae)
Bacteria
Leeuwenhock was the first biologist who observed and reported about bacteria in 1675. These were described as unicellular micro-organisms. These are named as animalcules.
They are described as microscopic, unicellular, achlorophyllous or chlorophyllous organisms. Bacteria multiply by binary fission.
Bacteria are cosmopolitan in distribution. These are found every where in soil,water, atmosphere and on or inside the living organisms. It has been found that they occur upto a few metres deep in the soil, deep sea water, hot water springs and ice.
They being unicellular micro organisms, their size and shape varies according to the species. Majority of the bacteria are in the range of 0.5-1.0 × 2.0-50 m in size. However, the smallest bacterium, Pasturella is of 0.2 × 0.3-0.7 m and the largest bacterium Beggiota is 15-22 m in diameter and several microns in length. Bacteria are of following four types.
Shape of Bacteria
1. Cocccus : Spherical bacteria.
(a) Monococcus A single spherical bacterium.
(b) Diplococcus A pair of bacteria.
(c) Streptococcus A long chain of spherical bacteria found in a single row.
(d) Sarcina These are arranged as cubes of eight bacteria.
(e) Staphylococcus: They are found in a group and arranged in irregular shapes.
2. Bacillus : These are rod-shaped bacterium.
(a) Monobacillus A single, rod shaped bacterium
(b)Diplobacillus Arranged in pairs and they are rod shaped.
(c) Streptobacillus Rod-shaped bac teria and are found in the form of a chain.
3. Vibrio : Coma-shaped bacterium.
4. Spirillum : Spring-shaped or helically coiled shaped bacteria.
Flagella
Atrichous : Flagella are not present.
Monotrichous : On the side of the cell is found a single flagellum.
Lophotrichous : A tuff of flagella are present which are attached to one side of the cell.
Amphitrichous : Two tuffs of flagella are on either end of the cell.
Peritrichous : All over the cell surface many flagella are distributed.
Protoplasm
There are three inside the cell wall in which protoplasm present can be differentiated. They are (i) Cell membrane (ii) Cytoplasm and (iii) Nucleoid.
Nutrition
Autotrophic bacteria : The in-organic substances absorb from the environment by green plants are converted into organic substances.
Heterotrophs : Heterotrophs are those which cannot make use of CO2 and meet their carbon requirements from organic substances like glucose and amino acids.
Photo-autotrophs : Photo-autotrophs are chlorophyll possessing bacteria just like green plants. They obtain energy from sunlight and carbon from environmental carbon dioxide. Purple sulphur and green sulphur bacteria belong to this group.
Photo-heterotrophs : These bacteria get energy from sunlight. They obtain carbon from organic substances. Examples are non-sulphur purple bacteria like Rhodospirillum Rhodopseudomones and Rhodomicrobium.
Chemo-autotroph : As the name indicates, this group of bacteria takes the carbon from carbondioxide and energy from the oxidation of inorganic substances. Examples are Hydrogen bacteria, colourless sulphur bacteria and nitrifying bacteria.
Chemo-heterotrophs : This group of bacteria derives both carbon and energy from organic substances like glucose and amino acids.
Saprophytes : These bacteria grow on dead and decaying substances e.g. Bacillus.
Parasites : These bacteria grow on the plants and animals which are living ones. e.g: Xanthomonas, Salmonella.
Symbionts : These bacteria make mutually beneficial association with other organisms. e.g: Rhizobium in the root nodules of legume plants.
Staining properties of bacteria : Bacterial staining method was suggested in 1884 for the first time by Gram. In this method previously bacteria are stained by alkaline violet crystals. In this process all bacterial cells take violet colour. Then bacteria which become violet are called Gram positive and remaining colourless bacteria are called Gram negative.
Reproduction in Bacteria : There are two methods used by bacteria for reproduction namely vegetative and asexual methods. Some bactria do conjugation type of sexual reproduction.
Vegetative Reproduction
(i) By budding : According to Bisset and Hale, the bacteria Bingid bacterium bifidus reproduce by budding.
(ii) By binary fission : Binary fission is the most common way of reproduction in all kinds of bacteria. Under favourable conditions bacterial cell expands. Cytoplasm divides into two parts due to construction and formation of a transverse septum in the centre of the cell. Finally, these two parts separate out from each other and produce two cells.
Asexual reproduction : There are three methods of asexual reproduction viz. (i) By endospores (ii) By conidia (iii) By zoospores.
Sexual reproduction—It was believed for a long time that in bacteria sexual reproduction does not take place. Laderberg and Tatum (1946) proved that sexual reproduction takes place in bacteria. For this discovery they were awarded Nobel Prize.
Now it has been proved that three types of sexual reproduction are found in bacteria.
Economic Importance of Bacteria
Useful Activities:
(a) Increase in soil Fertility : Soil fertility is increased by some bacteria. Nitrogen is essenial for all plants. Atmosphere contains about 78% of nitrogen. The plants take nitrogen in the form of nitrates. There are following three methods by which nitrates are formed in the soil.
(i) By nitrogen fixing bacteria : Bacteria are found in soil both in free state e.g. azotobacter and clostridium or in root nodules of leguminous plants. e.g. Rhizobium leguminosarum. Atmospheric free nitrogen is converted into useful nitrogenous compounds by these bacteria.
(ii) Nitrifying bacteria : Nitrifying bacteria do the job of converting nitrogen of ammonia into nitrite e.g. nitrosomonas convert nitrite compounds into nitrates e.g. nitrobacter.
(iii) Decay of Dead Organisms : Some bacteria live on dead bodies of animals and plants and convert their complex compounds into simpler substances. These converted substances are mainly carbon dioxide, water, nitrates sulphates etc.
(b) In dairy : Milk contains Bacterium lactici acid and B. acidi lactici. These bacteria ferment lactose sugar found in milk to form lactic acid by which milk becomes sour and gets converted into curd.
Lactic acid bacteria bring together a protein found in milk which called casein and help in the formation of curd.
On freezing of casein of milk protein it is fermented by bacteria.
(c) Industrial uses of bacteria : Bacteria are useful in following products—
(i) Vinegar industry : Sugar solution is used in the manufacture of vinegar in the presence of Acetobacter aceti.
(ii) Alcohol and acetone : Acetone and butyl alcohol are manufactured by the bacteria clostridium acetobutylicum.
(iii) Fibre ratting : Fibre ratting is used to prepare fibres of jute, hemp and flax. In the preparation of flax, hemp and jute the ratting of stems of Linum usitatissimum(Flax = Hindi Sunn), Cannabis sativa (Hemp = Hindi Patson) and Corchorus capsularis (Jute) respectively is done.
(iv) Tobacco industry : Process of fermentation is used for developing flavour and taste in tobacco leaves. The bacteria used for this purpose are Bacillus megathenium mycococcus.
(v) Tea industry : Fermentation by Mycococcus condisans is used for curing of tea leaves is done. This is a process which develops a special taste in the tea leaves.
(vi) Tanning of leather : Some bacteria decompose fats which are found in skin of animal with the result that skin and hair are separated from each other and makes the leather ready for use.
(d) In Medicines : Bacterial actions are used in the manufacture of some important antibiotics. These are Bacillus brevis—antibiotic thyrothricin and B. subtilis—antibiotic subtelin. Vitamin B2 is manufactured by fermentative action of Clostridium acetobutylicum.
(e) Miscellaneous :
(i) Disposal of sewage : Some bacteria convert organic faecal substances e.g. dung, decaying leaves of plants, etc. into manure and humus in the disposal of sewage.
(ii) Human symbionts : Escherichia coli inhabitat the large intestine of man and other animals and it synthesizes vitamins.
Harmful Activities
(A) Disease caused in plants by Bacteria :
Name of bacteria Name of disease
1. Pseudomonas Potato wilt solanacearum
2. Erwinia Pear and Apple ameylevora fire blight
3. Agrobacterium Crown gall tumefaciens
4. Xanthomonas Citrus Canker citri
5. X. campestris Black rot of cabbage
(b) Reduction of soil fertility : Bacteria like Thiobacillus denitrificans and Micrococcus denitrificans convert nitrates and Ammonia into free nitrogen. This process is called denitrification which reduces soil fertility.
(c) Food spoilage : Some saprophyte bacteria destroy food stuffs made up of fishes, vegetables, butter etc. and make them poisonous Clostridium botulinum destroys meat and other proteinaceous vegetables.
(d) Cotton destruction : Cotton fibres are destroyed by Spirochaete cytophage bacteria.
(e) Penicillin destruction : Some bacteria produce penicillase enzyme which destroys penicillin.
Because the above named harmful and useful activities of bacteria it is said that—“Bacteria are our friends and foes”.
