Current Affairs 11th Class

They are present in rumen (first part of stomach) of cattles. This is simplest and most primitive group of bacteria. The cell wall of these bacteria is made of polysaccharides and proteins (peptidoglycans and muramic acid are absent in cell wall). Further branched chain lipids are present in plasma membrane of archaebacteria, due to which these can face extremes of conditions of temperature and pH. Archaebacteria are considered to be 'oldest of living fossils'. Three main groups of archaebacteria are following. (1) Methanogens : These are strict anaerobic bacteria and mainly occur in muddy areas and also in stomach of cattle, where cellulose is fermented by microbes. These are responsible for methane gas \[(C{{H}_{4}})\] formation in bio-gas plants, because they have capacity to produce CH4 from CO2 or formic acid (HCOOH). e.g., Methanobacterium, Methanobacillus, Methanosarcina and Methanococcus. (2) Salt lovers archaebacteria or Halophiles : These are also anaerobic bacteria, which occur in extreme saline or salty conditions (upto 35% of salt or NaCl in culture medium). A purple pigmented membrane containing bacteriorhodopsin is developed in sun-light in these bacteria, which utilizes light energy for metabolic activities (different from photosynthesis). e.g., Holobacterium and Halococcus. (3) Thermoacidophiles : These are the bacteria which are found in hot sulphur springs (upto 80oC). As against first two groups of archaebacteria, these are aerobic bacteria. These have the capacity to oxidize sulphur to \[{{H}_{2}}S{{O}_{4}}\] at high temperature and high acidity (i.e., pH 2.0), hence given the name Thermoacidophiles, i.e., temperature and acid loving. \[2S+2{{H}_{2}}O+3{{O}_{2}}\to 2{{H}_{2}}S{{O}_{4}}\]+ energy. e.g., Sulfobolus, Thermoplasma, Thermoproteus.

Monera (Monos – single) includes prokaryotes and shows the following characters : (1) They are typically unicellular organisms (but one group is mycelial). (2) The genetic material is naked circular DNA, not enclose by nuclear envelope. (3) Ribosomes and simple chromatophores are the only subcellular organelles in the cytoplasm. The ribosomes are 70 S. Mitochondria, plastids, golgi apparatus, lysosomes, endoplasmic reticulum, centrosome, etc., are lacking. (4) Sap vacuoles do not occur. Instead, gas vacuole may be present. (5) The predominant mode of nutrition is absorptive but some groups are photosynthetic (holophytic) and chemosynthetic. (6) The organisms are non-motile or move by beating of simple flagella or by gliding. (7) Flagella, if present, are composed of many intertwined chains of a protein flagellin. They are not enclosed by any membrane and grow at the tip. (8) Moneran cells are microscopic (1 to few microns in length). (9) Most organisms bear a rigid cell wall (Peptidoglycan). (10) Reproduction is primarily asexual by binary fission or budding. Mitotic apparatus is not formed during cell division. (11) The kingdom Monera includes true bacteria, mycoplasma, rickettsias, actinomycetes (ray fungi) etc. Microbiologists also include blue green algae (i.e., Cyanobacteria) under the group bacteria because of the presence of prokaryotic cell structure. Studies have established that the members of archaebacteria group are most primitive and have separated from eubacteria group very early in the process of evolution.      Study of bacteria is called bacteriology. Linnaeus placed them under genus vermes. Nageli classified bacteria under schizomycetes. Bacteria are unicellular, microscopic and cosmopoliton organisms. The branch of science, which deals with the study of microorganism and their process is called as microbiology. Antony Von Leeuwenhoek is known as father of microbiology and father of modern microbiology is Robert Koch. These are the smallest cell wall having prokaryotic cell. The bacteria constitute a highly specialised group of one celled plants. They differ from animals in having a rigid cell wall and being capable to synthesize vitamins. Bacteria were first seen by a Dutch lens maker, Antony Von Leeuwenhoek (1683) who named them animalcules. Louis Pasteur (1822-95) made a detailed study of bacteria and proposed germ theory of disease. Ehrenberg (1829) was the first to use the term bacterium. Robert Koch (1881) found that some diseases like tuberculosis, cholera in man, and anthrax in cattle is caused by bacteria. Lister introduced antiseptic surgery. He used carbolic acid for sterilization of surgical instrument. Pasturization theory was proposed by Louis Pasteur. (1) Size : They are 3 to 5 microns (1m = 1/1000 millimetre or about 1/25,000 inch) in length. A few species of bacteria are approximately 15m in diameter. (2) Shape : The bacteria possess the following forms : Cocci (Gk. Kokkos = Berry) : They are oval or spherical in shape. They are called micrococcus when occur singly as in Micrococcus, diplococcus when found in pairs as in Diplococcus pneumoniae, tetracoccus in fours, streptococcus when found more...

(1) Many species of Nostoc fix atmospheric nitrogen and thus increases soil fertility. (2) Reclamation of alkaline usar soils can be done by employing some species of Nostoc. (3) N. commune is consumed as vegetable in China and Japan.

Cyanobacteria have both beneficial and harmful effects in human affairs. Useful activities (1) Growth of cyanobacteria in hard water is most probably responsible for the deposit of limestones. (2) Since they grow, photosynthesis, multiply and ultimately die, thus adding organic matter to the soil and increasing its fertility. (3) Whereas some cyanobacteria act to breakdown rock, the species that live in hot springs actually build rocks. This they accomplish by depositing salts of calcium and silica within the gelatinous sheath of the algal cell wall. (4) Balls of Nostoc commune are collected, boiled and consumed as food by the Chinese and South Americans. The prepared food is called 'Yoyucho'. (5) Some cyanobacteria, such as Anabaena, Lyngbya etc. help in conservation of soil, thus checking soil erosion. (6) Few species of Anabaena and Aulosira are inoculated in ponds to check the development of mosquito larvae. (7) Certain cyanobacteria like Nostoc commune, Scytonema ocellantum, Aulosira fertissima are used for reclamation of usar (sterile alkaline) soil. Harmful activities (1) Their most harmful effect is undoubtedly the formation of blooms in bodies of water. (2) They choke the intake of water supply systems and give the water a disagreeable odour giving a fishy taste to drinking water. (3) Many cyanobacteria produce toxins. They are directly or indirectly harmful for human. e.g., Nostoc, Anabaena, Microcystes etc. Habitat : Nostoc is found in aquatic and terrestrial habitat. The alga forms a jelly like mass in which numerous filaments are embedded. When young, they are more or less spherical, solid and microscopic in size. With advance in age, the colony grows and becomes macroscopic. In species like N. amplissimum it attains the diameter of 30cm or almost equals to the size of hen's egg in N. punctiforme. A number of species of Nostoc on soil. They often swell up and glisten after rains and therefore called fallen stars. Morphology : The plant is filamentous and trichome are unbranched and appear moniliform.. All the cells of the trichome are similar in structure but at intervals are found slightly larger rounded, light yellowish, thick walled cells called as heterocysts. Trichome mostly breaks near heterocyst and forms harmogonia and thus they help in its multiplication. The heterocysts are intercalary and possess a very thick outer wall. Each heterocyst is connected with vegetative cells on two sides through prominent pores in the wall which later are occupied by a refractive cyanophycean granule called polar nodule. Each cell trichome in Nostoc has primitive nucleus and chromoplasm and very much resembles in all details to a cyanophycean cell. Vacuoles and definite chromatophores are absent. The cellwall is differentiated into two layers. Outside the cellwall there is a mucilaginous sheath. Due to confluence of various mucilaginous sheaths of filaments, a mucilaginous colony is formed. The cell is prokaryotic. Reproduction in Nostoc There is no sexual reproduction more...

Bacteria are our ‘friends and foes’ as they have both useful and harmful activities. Useful activities (1) In agriculture or In soil fertility : Some bacteria increase soil fertility. Nitrogen is essential for all plants. Nitrogen occupies 80% of the atmosphere. The plants take nitrogen in the form of nitrates. In soil, nitrates are formed by three processes : By nitrogen fixing bacteria : Bacteria are found in soil either free e.g., Azotobacter and Clostridium or in root nodules of leguminous plants e.g., Rhizobium leguminosarum. These bacteria are capable of converting atmospheric free nitrogen into nitrogenous compounds. Nitrifying bacteria : These bacteria convert nitrogen of ammonia into nitrite (NO2) e.g., nitrosomonas and convert nitrite compounds into nitrates e.g., nitrobacter. Decay of dead plants and animals : Some bacteria attack on dead bodies of plants and animals and convert their complex compounds into simpler substances e.g., carbon dioxide (CO2), water (H2O), nitrate (NO3), sulphate (SO4) etc. (2) In dairy : Bacterium lactici acidi and B. acidi lactici are found in milk. These bacteria ferment lactose sugar found in milk to form lactic acid by which milk becomes sour. Lactic acid bacteria bring together droplets of casein a protein found in milk and help in the formation of curd. On freezing of casein of milk protein it is fermented by bacteria with the result that foamy and soft substance, different in taste is formed. (3) In industries : From industrial point of view bacteria are most important. Some of the uses of bacteria in industries are as follows : Vinegar industry : Vinegar is manufactured from sugar solution in the presence of Acetobacter aceti. Alcohol and acetone : Clostridium acetobutylicum takes part in the manufacture of butyl alcohol and acetone. Fibre retting : By this process fibres of jute, hemp and flax are prepared. In the preparation of flax, hemp and jute the retting of stems of Linum usitatissimum (Flax = Hindi Sunn), Cannabis sativa (Hemp = Hindi Patson) and Corchorus capsularis (Jute) respectively is done. Tobacco industry : Bacillus megatherium is used for its fermentative capacity for developing flavour and taste in tobacco leaves. Tea industry : By fermentative action of Mycococcus condisans curing of tea leaves is done. By this process special taste is developed in the tea leaves. Tanning of leather : Some bacteria decompose fats which are found in skin of animal with the result that skin and hairs are separated from each other and this leather becomes ready for use. Disposal of sewage : Some bacteria convert organic faecal substances e.g., cow dung, decaying leaves of plants, etc. into manure and humus. Human symbionts : Escherichia coli inhabitats the large intestine of man and other animals and it synthesizes vitamins. (4) In medicines : Some of the antibiotics are manufactured by bacterial actions e.g., Bacillus brevis – antibiotic thyrothricin and B. subtilis – antibiotic subtelin. Vitamin B2 is manufactured by fermentative action of Clostridium acetobutylicum. Antibiotics : These are the chemical substances produces by living microorganisms capable more...

(1) Diseases in human beings : Mycoplamsa hominis causes pleuropneumonia, inflammation of genitals and endocarditis, etc. Mycoplasma pneumoniae causes primary a typical pneumonia (PAP), haemorrhagic laryngitis, etc. Mycoplasma fermentatus and M. hominis cause infertility in man, otitis media (inflamation of middle ear). (2) Diseases in animals : Mycoplasma mycoides causes pneumonia in cattle. Mycoplasma bovigenitalum, causes inflamination of genitals in animals. Mycoplamsa agalactia causes agalactia of sheep and goat. (3) Diseases in plants : Common mycoplasmal diseases of plants are: Bunchy top of papaya, witches' broom of legumes, yellow dwarf of tobacco, stripe disease of sugarcane, little leaf of brinjal, clover phylloidy, big bud of tomato etc. The new name of cyanobacteria has been given to myxophyceae or cyanophyceae. Cyanobacteria form a group of ancient Gram negative, photosynthetic prokaryotes. Many botanists prefer to call them blue-green algae. They have survived successfully for about 3 billion years. They may cause water blooms. Cyanobacteria are predominantly fresh water forms, a few are marine. They impart unpleasant taste and smell to the water. One species of cyanobacteria containing red pigment (Trichodesmium erythraeum) flourishes in red sea and is responsible for the red colour of its water. A few species grow in hot water springs having a temperature range of 70°–75°C (e.g., Phormidium, Hastigocladus) and other grow at very low temperature in the polar regions (e.g., Nostoc, Schizothrix, Microcoleus etc.).Some grow in the soil and help in fixation of nitrogen and utilize it in metabolism. Nostoc colony is found into the thallus of Anthoceros. Colonies of Nostoc and Anabaena grow in paddy fields. Anabaena cycadeae is found in coralloid roots of cycads.  Characteristics of Cyanobacteria (1) They have prokaryotic type of cells. (2) Cells do not have any organised nucleus. The nucleolus is absent and the nucleoid is not to be bounded by a nuclear membrane. The type of nucleus called incipient nucleus. (3) The photosynthetic pigments present in the cell are – chlorophyll a, b carotene, myxoxanthophyll, myxoxanthin, C-phycocyanin and C-phycoerythrin. The C-phycocyanin is blue and C-phycoerythrin is red in colour. If C-phycocyanin is more as compared to C-phycoerythrin, it gives characteristic blue- green colour to the algae. (4) The photosynthetic pigment are present in lamellae, called thylakoids. (5) The presence of chlorophyll–a, cyanobacteria synthesis their own food from carbon dioxide and water in the presence of sunlight. Certain cyanobacteria fix atmospheric nitrogen in the presence of oxygen. (6) In cyanobacteria food is stored as cyanophycean starch or a–granules.  (7) Some members possesses simple unbranched filament with heterocyst like Nostoc, Anabaena, Aulosira, Cylindrospermum etc. (8) Some members possesses simple unbranched filamentous forms without heterocysts and akinetes, e.g., Arthospira, Oscillatoria, Spirulina, Phormidium, Lyngbya, Symploca, Microcoleus, Schizothrix etc. (9) Cyanobacteria reproduce asexually by fission and fragmentation. Unicellular forms multiply by binary fission. Sexual reproduction is totally absent. (10) Flagella are completely absent but the movement occurs in some genera by special gliding motion. Such movements are connected with the secretion of mucilage. The genus Oscillatoria exhibits pendulum more...

On the basis of mode of nutrition, bacteria are grouped into two broad categories. First is autotrophic and second is heterotrophic bacteria.    Autotrophic bacteria : These bacteria are able to synthesize their own food from inorganic substances, as green plants do. Their carbon is derived from carbon dioxide. The hydrogen needed to reduce carbon to organic form comes from sources such as atmospheric \[{{H}_{2}},{{H}_{2}}S\] or \[N{{H}_{3}}.\]These are divided into two categories.   (1) Photoautotrophic bacteria : These bacteria are mostly anaerobic bacteria. They use sunlight as source of energy to synthesize food.  They possess a pigment called bacteriochlorophyll which is different from the chlorophyll pigment found in higher plants. This is known as anoxygenic photosynthesis. e.g., Green sulphur (Thiothrix) and purple sulphur (Chromatiun) bacteria. They can perform photosynthesis in far-red light. Rhodospirillum bacteria fixes \[C{{O}_{2}}\] into carbohydrate (Photoautotrophic).   Green sulphur bacteria : They are autotrophic. The hydrogen donor is \[{{H}_{2}}S\] and the pigment involved in the process is chlorobium chlorophyll (Bacterioviridin) e.g., Chlorobium.   \[6C{{O}_{2}}+12{{H}_{2}}S\underset{\text{Chlorobium}\,\,\text{chlorophyll}}{\mathop{\xrightarrow{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}}}\,{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+12S\].   Purple sulphur bacteria : They are also autotrophic. The hydrogen donor is thiosulphate and the pigment involved in photosynthesis is bacteriochlorophyll e.g., Chromatium.   \[6C{{O}_{2}}+15{{H}_{2}}O+3N{{a}_{2}}{{S}_{2}}{{O}_{3}}\underset{\text{Bacteriochlorophyll}}{\mathop{\xrightarrow{\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,}}}\,{{C}_{6}}{{H}_{12}}{{O}_{6}}+6{{H}_{2}}O+6NaHS{{O}_{4}}.\]   Purple non-sulphur bacteria : They are heterotrophic utilizing succinate or malate or alcohol. e.g., Rhodospirillum, Rhodopseudomonas.   \[6C{{O}_{2}}+12C{{H}_{3}}CHOHC{{H}_{3}}\xrightarrow{{}}{{C}_{6}}{{H}_{12}}{{O}_{6}}+12C{{H}_{3}}COC{{H}_{3}}+6{{H}_{2}}O.\]   (2) Chemoautotrophic bacteria : Some bacteria manufacture organic matter form inorganic raw materials (such as carbon dioxide) and utilize energy liberated by oxidation of inorganic substances present in the external medium such as ammonia, ferrous ion, nitrates, nitrites, molecular hydrogen, etc. The energy liberated from exergonic chemical reactions is trapped in the ATP molecules which is used in carbon assimilation to synthesize organic matter.   Sulphur bacteria : These bacteria derive energy by oxidizing hydrogen sulphide or molecular sulphur. Beggiatoa, a colourless sulphur bacterium oxidises hydrogen sulphide \[({{H}_{2}}S)\] to water and sulphur. The energy released is used up and the sulphur granules are deposited inside or outside the body of bacterial cell.   \[2{{H}_{2}}S+{{O}_{2}}\xrightarrow{{}}2{{H}_{2}}O+2S+\text{Energy}\].   Iron bacteria : Some chemoautotrophic bacteria such as Gallionella, Sphaerotilus, Ferrobacillus, etc, inhabit the environments where irons to ferric form. The Ferric ions are deposited in the form of soluble ferric hydroxide and the energy released during the conversion is used in the production of carbohydrates.   \[4FeC{{O}_{3}}+{{O}_{2}}+6{{H}_{2}}O\xrightarrow{{}}4Fe{{(OH)}_{3}}+4C{{O}_{2}}+\text{Energy}\,\text{(81}\,\text{k}\text{.cal)}\]   Hydrogen bacteria : These bacteria utilize free molecular hydrogen and oxidize to hydrogen into water with the help of either oxygen or oxidize salts e.g., Hydrogenomonas. \[2{{H}_{2}}+{{O}_{2}}\to 2{{H}_{2}}O+\text{Energy}\] (56 kcal). Amonifying bacteria : They oxidise protein and amino acid into NH3 (ammonia). e.g., Proteus vulgaris, Bacillus mycoids. Nitrifying bacteria : They oxidise ammonia to nitrites and then into nitrates.   \[N{{H}_{3}}+{{O}_{2}}\xrightarrow{\text{Nitrosomonas}}N{{O}_{2}}+{{H}_{2}}O+\text{Energy}\] and    \[2N{{O}_{2}}+{{O}_{2}}\xrightarrow{\text{Nitrobacter}}2N{{O}_{3}}+\text{Energy}\].   Denitrifying bacteria : They change nitrogen compound into molecular nitrogen. So that they reduce fertility of soil e.g., Micrococcus denitrificans, Pseudomonas denitrificans.   Methane bacteria : The bacterium Methanomonas utilizes methane as source of carbon and energy.   \[C{{H}_{4}}+2{{O}_{2}}\xrightarrow{{}}C{{O}_{2}}+2{{H}_{2}}O+\text{Energy}\].   Methane producing bacteria : These are spherical or rod shaped bacteria which produce methane \[(C{{H}_{4}})\] from hydrogen gas more...