What are Prokaryotes? 

• As the name indicates, pro means primitive & karyon means nucleus. In short, the primitive nucleus organisms are referred to as the prokaryotes.
• By the primitive nucleus, we simply mean, a nucleus that is not bound by a distinct nuclear membrane from outside such that their genetic material remains suspended freely in the cytoplasm of their cell.
• Being the prokaryotes, they were the first organisms to have evolved on the Earth when the evolution of life first began on this planet somewhere, around 3.6 billion years ago and may be compared to the present day bacteria.
•  Today the prokaryotes comprise the following three kinds of organisms, all included in the kingdom Monera:
• The bacteria
• The Cyanobacteria &
• The Mycoplasmas; also called as PPLO.
• They all are noted for having a primitive cellular structure that is covered from the outside by a cell wall that in its chemical composition is absolutely different from the one present in a plant cell.
• This distinct cell wall composition and structure probably had enabled them to survive under extremely hostile conditions present on the earth when they first evolved on it and even found today under similar tough and hostile conditions.
• Noted that among all the prokaryotes, it is only the Mycoplasmas that are devoid of a cell wall and hence, constitute an exception as a result of this, they can easily change their shapes and thus, are also described as the joker’s of Microbiology.
• They are all pathogenic in nature and hence, discovered as such for the first time among cattle in being the casual organisms of a lung infection. For this reason, they are also called as PPLOs (pleura pneumonia like organisms).
• Nevertheless, all prokaryotes are noted for having a similar cellular structure characterized for the presence of following prominent cellular structures:
• *Cell wall: Chemically made up of Peptidoglycan that is a mixture of proteins and complex carbohydrates that are generally polysaccharides. This is in contrast to the cell wall composition of a eukaryotic cell, like a plant where it is made up of cellulose.
• *Flagella: A locomotory structure in prokaryotes, made of a material called as Flagellin.
• *Nucleoid or Genophore: A region in the cell cytoplasm where their genetic material remains concentrated. Their genetic material (DNA) is however, a single chromosome only
• *Plasmids & Mesosomes: Plasmids refer to the extra-nuclear DNA present exclusively in prokaryotes. Mesosomes are considered as the bacterial Mitochondria and are a site of respiration. Since the discovery of these small ringlets of DNA in bacteria called as Plasmids, they have been used as one of the most important tools of biotechnology. Being used as cloning vectors in Biotechnology, plasmids are being used as so called molecular ferries for transporting a foreign piece of DNA after being fused or ligated to it and then sealed with the help of molecular adhesives called as DNA-Ligases.
• * Ribosomes:  Probably, the only common cell structures found in both Prokaryotes as well as Eukaryotes and perform the same role of protein synthesis in both types of cells. However, the prokaryotic ribosomes are noted for being 70-S type and refer to prokaryotic ribosomes. Similar ribosomes are also found inside the Eukaryotic mitochondria & plastids. Thus, it is sometimes said that both of the above cell organelles are believed to be the bacterial endosymbionts.
• Useful Prokaryotes:  The beneficial bacteria which have served the man kind since ages in terms of their use either in the production of life saving drugs especially, antibiotics or their use in the industrial production right from various organic acids to their use most famously, in dairy industry.
• Simultaneously, the single most prokaryotes that have been used extensively in the Agriculture industry across the world and have been entitled as the biofertilizers are the famous BGA or cyanobacteria. Their property of being the biofertilizers owe to their unique quality of fixing the atmospheric molecular nitrogen and converting the same into nitrates.

Diseases caused by Bacteria

• What are Eukaryotes?  They are simply defined as the true nucleus organisms that came after the prokaryotes on this earth around 2 billion years ago. The first ever Eukaryotes however were unicellular from which the entire complex and advanced life originated gradually through evolution that occurred unstoppably over millions of years and is still underway. Their cell structure is not only characterized by having a clear cut demarcation between the nucleus and the cytoplasm, but also displays the property of being a self-sufficient, organized structure that is capable of existing an independent life. This independent existence is enabled to a eukaryotic cell by the presence of specialized structures in it what we call as cell organelles, each is specialized to perform its specific role in the cell. Herein below follows a schematic diagram to explain the organization of a Eukaryotic cell:

Individual function of different cell organelles: 

Main CELL ORGANELLES:

• Mitochondria: They are called Powerhouse of the cell because they are the major centers of release of energy in the aerobic respiration. They were first observed by Kolliker in 1880. Benda gave the present name of Mitochondria.
• Plastids: They store or synthesis various types of organic compounds.
• Golgi complex: Golgi complex is a complex Cytoplasmic structure that takes part in membrane transformation, secretion and production of complex biochemicals.
• Lysosomes (Lysis – digestive or loose, soma – body): These are small vesicles, which are bounded by a single membrane and contain hydrolytic enzymes in the form of minute crystalline or semi-crystalline granules of 5-8 micrometer.
• Lysosomes take part in digestion of food obtained through Phagosomes.
• They take part in natural defence of the body.
• Obstructing structure is destroyed by lysosomes.
• In thyroid, active hormone thyroxin is formed through hydrolysis of thyroglobulin by the agency of lysosomes.
• Ribosomes / Palade particles: A large number of ribosome’s occurring in a cell. For example, a single cell of bacterium Escherichia coli contains 20000 – 30000 ribosomes. These are naked ribonucleoprotein Protoplasmic Particles (RNP) with a length of 200 – 340A0 and diameter of 170 – 240A0, which function as the sites for protein or Polypeptide Synthesis.
• Ribosomes are popularly known as Protein factories. Eukaryotic cell contains 80s type ribosome’s and Prokaryotic (e.g. Bacteria) contains 70s type ribosome’s.
• Nucleus: Nucleus is double membrane bound protoplasmic body, which contains all the genetic information for controlling cellular metabolism and transmission to the posterity.
• Nucleus is the largest cell organelle. Nucleus was first studied in orchid root cell by Robert Brown in 1831. A Nucleus is present in all living eukaryotic cells with the exception of nature sieve cells of vascular plants and red blood corpuscles of mammals…

Though a number of classification systems were devised to classify the living world from time to time. However, the classification system given by R.H.Whittaker in 1969 to classify the living world is the most authentic and universally followed today. According to this system of classification, the entire living world is classified into the following 5 kingdoms:

Kingdom Monera

Kingdom Protista

Kingdom Fungi

Kingdom Plantae

Kindom Animalia.

Kindom monera includes all unicellular prokaryotes that were the first organisms to have evolved on this earth. In simple terms, all bacteria of any type and present anywhere on this planet are included in this kingdom. In strict Biological terms, this kingdom includes all prokaryotes which invariably are unicellular in nature.

Bacteria

Bacteria are generally called as the friends and foes of mankind, but in terms of actual significance they have for the mankind, their friendly use outweigh their being unfriendly or harmful to the mankind just because the bacteria do not only play a significant ecological role in the whole of the biosphere by acting on the dead organic matter, but also have a great commercial and economic significance for the mankind on account of their being involved or used in a number of biological processes to derive a variety of products & services useful to the mankind which the man knows right since the advent of human civilization. Herein below we shall study some of their economic significance:

§  Bacteria in Agriculture or in soil fertility: In agriculture or soil fertility, the immense role of bacteria comes from their ability to fix the atmospheric nitrogen which is abundantly present in the atmosphere. Since, the plants cannot directly use this atmospheric nitrogen unless, it is converted into their usable form called as nitrates. In the soil, this nitrate is formed by the action of bacteria by way of following two methods:

§  By nitrogen fixing bacteria: These bacteria in the soil are present either freely or in some symbiotic forms. While the free living nitrogen fixing bacteria in the soil may be mentioned as Azotobacter, Beijerinckia, Klebsiella whereas, the symbiotic bacteria that live in a symbiotic relationship with other plants such as Rhizobium legumenosarum that lives in the root nodules of legumes such as pea or Frankia that lives in the root nodules of non-legumes e.g. Casuarina and Alnus. Similarly, another bacterium called as Xanthomonas lives in the leaf nodules of another plant called Ardisia is also a known nitrogen fixer. Owing to the capability of these bacteria to convert the atmospheric free nitrogen into nitrates, these bacteria are therefore called as the natural fertilizers of the soil or more appropriately, as the biofertilizers and this explains the logic of growing the legume plants in crop rotations.

§  By nitrifying bacteria: As the plants or animal die, they are acted upon by certain soil born saprophytic bacteria to break down their proteins to release the nitrogen that goes down into the soil and converted into ammonia under a process called as ammonification. Since, ammonia cannot be readily utilized by the plants; the same is therefore reacts with the soil water to form ammonium hydroxide to be later converted into ammonium salts. The nitrifying bacteria present in the soil then convert this ammonia or ammonium salts into nitrates through a process called as nitrification. This nitrate as usual is being utilized by green plants as a principal source of nitrogen. The most important bacteria involved in this process are Nitrosomanas, Nitrosococcus & Nitrobacter etc.

§  The sulphur bacteria as a source of sulphates to green plants: Just like the ammonifying and nitrifying bacteria act as a source of nitrates to the green plants, the sulphur bacteria act as a source of most important sulphates for them. In this process, the sulphur bacteria present in the soil act on the hydrogen sulphide, a product of protein destruction formed after the death of an organism in the soil. The sulphur bacteria convert this hydrogen sulphide into sulphuric acid which then reacts with some salts to form the sulphates that become the major source of sulphur for the metabolism of green plants. The most important bacteria involved in this process are Thiobacilli.

§  2) Bacteria as decomposers: As decomposers, they perform the following important roles:

i)    Decay of dead plants & animals: This way they convert the complex organic materials into their simplest forms that ultimately get absorbed in the soil and thus increase the soil fertility. Bacillus mycoides and B.vulgaris are the typical examples in this category.

ii) Decomposers of petroleum from oil spills: Some oil eating bacteria are present naturally on ocean beaches that clear the oil spills by decomposing the petroleum by feeding on it. However, in recent years, an Indian scientist made a genetically modified or engineered oil eating bacteria named “Super Bug” that could feed on oil spills in high seas and hence, proved to be of great significance in saving the other marine life. This super bug today is called as *Pseudomonas putida. (Question asked in GS-Pre.2010.)

iii) Decomposers of sewage: Some bacteria can degrade the complex organic material of the sewage into harmless, soluble and inorganic form of materials through a process called as mineralization whereby, the sewage is separated into a liquid and sludge in the special settling tanks. A combination of aerobic and anaerobic bacteria is then released into the sludge and hence, water is reclaimed from the sewage that may well be fit for human consumption. While this use of bacteria might give an answer for meeting out the future scarcity of drinking water resources, the methane gas produced as a result of anaerobic decomposition of sewage by the bacteria such as Methanococcus and Methanobacterium can be used as a biogas fuel.

§  Bacteria in Dairy industry: This probably is the first beneficial use of bacteria exploited by man. The bacteria like Streptococcus lactis and Lactobacillus lactis are found naturally in milk that act on the lactose sugar of the milk to form the lactic acid that finally coagulates the milk protein called as casein by which milk becomes sour and hence, we get the curdled form of milk what we call as curd. Since, the above milk bacteria are present naturally in milk and can spoil the milk, the milk is therefore subjected to pasteurization by heating the same at 62.8 C for 30 minutes or at 72C for 20 seconds. It is pertinent to note that the manufacture of almost all milk products such as curd, butter, cheese and ghee is entirely based on the bacterial activity. The role of bacteria in the dairy industry is so vast that it has today given birth to a new offshoot of biology called as Dairy Bacteriology. The role of some of the prominent bacteria here may be mentioned as below:

§  CURD: Streptococcus lactis

§  CHEESE: Lactobacillus lactis

§  BUTTER: Streptococcus lactis

§  YOGHURT: Lactobacillus bulgaricus

§  BUTTERMILK: Streptococcus cremoris.

Industrial value/use of bacteria

§  In the production of Vinegar: The bacteria called as Acetobacter aceti and Mycoderma aceti are the prominent bacteria used in the commercial production of vinegar so called Acetic acid. In this process, first of all the carbohydrates are fermented to ethyl alcohol by the action of Yeast. The alcohol thus formed is then subjected to the action of the above mentioned aerobic bacteria that oxidize the same into acetic acid or Vinegar. Noted that the acetic acid so produced may be subjected to the action of some another bacteria such as Clostridium acetobutylicum to form butyl alcohol and acetone.

§  In Fibre retting: In this process, the fibres are separated from fibre yielding plants like Linum, commonly called as flax or sunn. Similarly from Cannabis (hemp or patson) or Corchorus capsularis (Jute). In this process, the specific bacteria decompose the pectin of the plant material to liberate the fibres. This process of fibre separation is called as retting and the noteworthy bacteria involved in this process are Clostridium butyricum and Clostridium pectinovorum that naturally inhabit the water.

§  Bacteria in Tobacco industry: Bacteria such as Bacillus megatherium and Micrococcus candidans are used for their fermentative capacity for developing flavour and taste in tobacco leaves.

§  Bacteria in Tea industry: Micrococcus candidans is used in curing of tea leaves by using their fermentative capacity such that a special flavour and taste is developed in tea leaves.

§  Bacteria in Leather industry: Tanning of skin leather is done with the help of certain bacteria and thus leather is obtained for ready use.

§  Role of Bacteria in genetic analysis: The significance of bacteria in genetic analysis stems from the fact that they are unicellular and have a high replication or division rate say, E.coli, the most common experimental bacterium has a high division rate of dividing once in every 20 minutes and in an hour produces three new generations thereby, offering an ease of working with bacteria to complete a genetic experiment in a matter of an hour or so while, for performing a similar experiment with a multicellular organism might take months or even years owing to their long generation times. It does not surprise us that the injectible insulin available in the market today for diabetics is entirely being produced from the bacterium E.coli through recombinant DNA technology. Produced for the first time using the above bacterium in 1990 by an American pharma major, Elliy Lilly under the brand name of humulin, was also the first ever GMO drug to be marketed and commercialized in the world and bacterium E.Coli became instrumental in this GMO drug revolution.

§  Role of bacteria in controlling insect pests & birth of bio-pesticides: A naturally occurring soil bacteria called as Bacillus thuringiensis, commonly referred to as Bt. It is noted for producing a protein toxin that is lethally effective against a variety of insect pests that are destructive to almost all of our crops. Such crop insect pests include a variety of caterpillars and worms such as boll worms, Alfalfa caterpillars have been found quite destructive to commercial crops such as cotton & others. Following the birth of recombinant DNA technology, the specific toxin producing gene from this bacterium has been isolated and introduced into various crops to make them pest resistance, a breakthrough first achieved in the production of Bt. cotton and subsequently, many more Bt. crops were produced through the marvel of genetic engineering. In America however, Bt. bacterium is mass produced by commercial companies and is sold in a powdery form of its spores packed in sachets to be sprayed on food crops. These spores are absolutely harmless to humans, birds, animals or to any other soil organism except to above pests. Thus, once a caterpillar or its larvae ingest these spores, the bacterium gets quickly active in their gut & multiplies and the caterpillar stops feeding, turns black and drops off the plant and dies within 2-4 days time. Talking once again in the context of recombinant technology use of Bt. bacterium as a potent bio-pesticide, the toxin producing gene called cry gene has been isolated from it and then introduced into another bacterium named Pseudomonas fluorescence via genetic engineering that is now used against black cut worms. Notwithstanding this, a variety of Bt. bacterium named B.israelensis, acronymed as BTI is being used commercially to control mosquitoes especially, against their larvae (wrigglers). Whereas, another bacterium called B.popillae is also being marketed commercially in powdered form against the highly destructive Japanees beetle.

§  Role of bacteria in the production of antibiotics (Medicines): An antibiotic is certainly the wonder drug of today that is being produced by a living organism against another organism and this is how the antibiotics are capable of inhibiting the growth of other pathogenic micro-organisms. Man has isolated a number of such antibiotics from bacteria such as an antibiotic named thyrothricin has been derived from a bacterium called Bacillus brevis. Similarly, another antibiotic named subtelin has been derived from a bacterium called Bacillus subtilis. Some of the highly effective antibiotics having been obtained from different bacteria may be mentioned as below:

§  Streptomycin from Streptomyces griseus (Discovered by Waksman in 1944 for which he was awarded Nobel in 1952.)

§  Chloromycetin also as (Chloramphenicol) from S.venezuelae.

§  Aureomycin also as (Chlortetracycline) from S. aureofaciens.

§  Terramycin also as (Oxytetracycline) from S. rimosus.

§  Neomycin from Streptomyces fradiae.

§  Erythromycin from S. erythraeus.

§  Kanamycin from S. kanomyceteus and

§  Polymyxin B is derived from Bacillus polymyxa.

§  Miscellaneous beneficial applications of bacteria of kingdom Monera: A gamut of miscellaneous product and services that the bacteria have also been found to be of great economic significance may be mentioned as below:

§  As cellulose digesters in the gut of ruminants: All herbivores especially the cud chewing ruminants like cow are known to host certain cellulose digesting bacteria in their intestinal tract called as methanogens. These methanogens are actually a source of gobar gas that is being derived from the dung of these ruminants and is chemically known as methane.

§  As a source of vitamins: It is indeed a well known fact that a bacterium known as E.coli is known to live in human large intestine as a symbiont is noted for synthesizing some important vitamins especially, vitamin K that has been known to be an anti-haemorrhagic vitamin. Similarly, another vitamin named Riboflavin, a kind of vitamin B2 is synthesized by Clostridium butylicum as a result of fermentation of sugars and starches. Another bacterium named Propionibacterum sharmanii as well as Pseudomonas dentrificans are to synthesize vitamin B12 so called as cyanocobalamine. One bacterium called Acetobacter is used for synthesizing ascorbic acid commonly called as vitamin C.

§  As a source of Enzymes: A number of enzymes that are of great commercial value in the food industry has been synthesized from bacteria such as a group of enzymes called proteases are derived from bacteria called as Bacillus subtilis. Similarly, the enzyme called as streptokinase is produced from another bacterium called as Streptococcus pyogenes. Noted that streptokinase is also called as TPA that stands for Tissue Plasminogen Activator, a wonderful enzymic substance in the domain of medical science used to clear the blood clots inside the blood vessels. An enzyme called as Renin that is commercially sold as rennet tablets and used for curdling the milk has been derived today from a genetically engineered bacteria. At last, but not the least, some other uses of bacteria have been in the following areas of great economic significance:

§  Bacteria in genetic Engineering: It won’t be out of place to say that the birth of modern biotechnology or so called recombinant technology owes entirely to the use of bacteria. One of the vital tools of biotechnology, an enzyme called as restriction endonuclease has been discovered but from the bacteria without which gene manipulation after being cut from a DNA strand would have not been possible. This how, the above bacterial enzymes have earned the epithet of molecular scissors. Similarly, another vital tool of biotechnology are the small ringlets of DNA present only in bacteria outside their nuclear DNA and are called as Plasmids, are being used in modern biotechnology as molecular ferries that carries the foreign DNA into the host for deriving that foreign genes multiple copies.

§  Bacteria for carcinogen screening: A carcinogen is any substance that is cancer inducing in nature. Many types of such carcinogens are being tested through certain bacteria most importantly, Salmonella.

§  Bacteria for the extraction of metals from their minerals: Some bacteria can be used in this regard through a process called as leaching. Metals such as copper may be extracted by using certain strains of bacteria from rocks especially when the metallic concentration is very low in such a rock(s).

§  Bacteria as pollution fighters: This ecologically significant role is played by bacteria by converting a chemically harmful substance into a harmless one after being broken down into inorganic minerals that are subsequently reabsorbed by the plants themselves. Ecologically, these bacteria constitute an important like of Detritus food chain. Some of these bacteria live naturally in soil that can degrade pollutants of any nature and kind…

CYANOBACTERIA

Cyanobacteria were previously called as BGA (Blue green Algae) owing to the presence of a special pigment in them called as Phycocyanin giving them a blue green color. Therefore, they are also sometime called as Cyanophycean algae. Their economic significance in the field of agriculture is so vast that today they are being dubbed as *Biofertilizers and their increasing use in agriculture has both ecological and economic significance of a vast proportion. The blue green algae as *biofertilizers are noted for their ability to fix the atmospheric nitrogen into nitrates, a form which the green plants only are capable of using for their growth and metabolism.* (Question asked in GS-Pre.2010.) The most important BGA noted for having this property are Nostoc & Anabaena which today’s agriculture experts recommend their being cultivated alongwith other food crops thereby, increasing the fertility of the soil and ofcourse, obviating the use of chemical fertilizers for replenishing the soil fertility. Nevertheless, some Cyanobacteria especially, Nostoc are also used for their ability to convert the barren clay soil into a fertile cultivable land. Of late, the agriculturists have been growing a small aquatic fern plant called Azolla along with the rice crops as a biofertilizers as the Azolla is known to have a cyanobacterium inside it in a symbiotic relationship. The specialized structures present in the cyanobacteria in which nitrogen fixation take place are called as heterocysts.

Note: Sometimes, a number of species of cyanobacteria especially, Nostoc grows on the soil. They often swell up and glisten after rains and therefore, called fallen stars. No wonder, in China and Japan, a species of Nostoc called as Nostoc commune is consumed as vegetable