Transgenic Microbes: 6 Things to Know About Transgenic Microbes

Read this article to learn about Transgenic Microbes:-

(1) Microbes in Human Welfare (2) Microbes in Industrial Production (3) Microbes in Sewage Treatment (4) Microbes in Energy Generation (5) Microbes as Bio-pesticides and (6) Microbes as Bio-fertilizers.

The microorganisms which carry foreign genes are called transgenic microbes. A number of microbes (e.g., Lactobucillus, Leuconostoc, Bacillus, Streptomyces, Yeast, Rhizopus, Penicillium, Aspergillus) are employed commercially in preparation of Yoghurt, cheese, alcoholic drinks, vinegar, lactic acid, enzymes, vitamins and antibiotics. They have been improved through mutations to provide higher yield. For example, yield of penicillin was quite low in the beginning so that its cost was very high.

With continuous efforts high yielding strains were developed so that its price became affordable. At present, along with mutagenesis, genetic engineering is being employed to obtain desired biochemical from microbes (microbial biochemical factories). Human insulin (humulin) was the first biochemical to be produced commercially by this technique.

1. Microbes have been modified (e.g., Escherichia coli) through recombinant DNA technology for mass scale production of human insulin, interferon’s, human growth hormone, tissue plasminogen activator, epidermal growth factor, fertility hormones, lung surfactant protein factor VIII, interlenkin 2, and viral vaccines.

2. Nif region of Klebsiella with five operons made of 15 genes was recombined to plasmid pule- 120 and introduced in Escherichia coli. Escherichia coli started nitrogen fixation.

3. Bacillus thuringiensis has yielded endotoxin for control of insects.

4. Pseudomonas fluorescence has provided biochemical for preventing frost damage.

5. Rhizobium meliloti has been improved for efficient nitrogen fixation.

6. A number of fungi are providing chitinases for controlling fungal diseases.

7. Removal of lignin from wood pulp can be carried out by Trametes and other microbes.

8. Pseudomonas has become useful in bioremediation or purification of environment polluted by heavy metals, petroleum products and several other chemicals.

9. Fungus Trichoderma is being employed for bio control against a number of plant diseases and pests. Rhizobium is being used as important bio fertilizer.

10. Pseudomonas putida has been modified through introduction of plasmids for alcoholic fermentation.

Thing # 1. Microbes in Human Welfare:

Microorganisms are one of the most important partners in our life. Their presence is felt by human beings in one way or the other through the major part of the day. They may be called worst of our enemies but at the same time they are among the best of our friends. Hence, one cannot forget the gifts, which have been given by these organisms to this world except the harmful effects.

Some of the beneficial contributions of the microorganisms to the world are follows:

Microbes in Household Food Processing:

Fermentation, as one of the household microbial activities, is known to early man. He practiced fermentation processes while preparing curd, alcoholic beverages, vinegar etc.

A. Curd:

The Lactic acid bacteria (LAB), such as Lactobacillus bulgaricus and Streptococcus thermophiles, convert milk into curd, which is also used in the production of yogurt. While preparing the curd, a small amount of curd is added to fresh milk as starter or inoculum, which contains millions of LAB, and convert milk into curd, under suitable temperature. LAB also improves the nutritional quality of curd by increasing vitamin B₁₂.

B. Cheese:

Cheese is one of the oldest food items in which microbes are used. Cheese is the partially degraded concentrate of milk fat and casein, produced by the microbial activity. Cheese is used as a food item all over the world, and there are different varieties of cheese, which are characterized based on their texture, flavour and taste; the specificity being attributed to the biochemical activities of specific microbes. In preparing cottage cheese, streptococcus lactis and Lactobacillus are used as the inoculum to convert milk into curd. After separating the curd from whey, little salt is added and cakes or balls.

C. Dough:

It is used for making foods such as idli, dosa, Jilebi, bread etc.; these are also fermented by bacteria. The dough, which is used for making idli and dosa, is usually kept for 10 to 13 hours or overnight, to ferment. The fermentation is caused by the bacteria (Leuconostoc mesenteroides and Pedicoccus cerevisiae) drawn from the environment; as a result the dough gets sour and increase in volume, due to release of carbon dioxide gas during fermentation. Similarly, the dough, which is used for making bread is fermented with baker’s yeast, Saccharomyces cerevisiae, with the production of CO₂ and alcohol.

Other Products:

Today, a traditional local drink, is prepared by fermenting sap obtained from toddy palm and coconut palm. Several other traditional drinks and food are made by fermentation using microbes.

Thing # 2. Microbes in Industrial Production:

Microbes are extensively used in industry to synthesis several products beneficial to humans. These mainly include beverages, antibiotics, organic acids, enzymes and vitamins.

A. Beverages:

Beverages are classified into alcoholic beverages (Beer, Wine, Brandy, Rum, Whisky etc.) and non­alcoholic beverages (coffee and tea). The yeasts, which bring about fermentation, are grouped into baker’s yeast and brewer’s yeast. The baker’s yeast, Saccharomyces cerevisiae, is used in baking industry. This is available in the market as baker’s yeast, in the form of powder or pellets. These yeasts ferment sugar in the dongh and employed in foods such as idli and dosa, bread and other bakery products referred to earlier.

Brewer’s yeast is employed in the brewing industry in t he preparation of alcoholic drinks. Different species of brewer’s yeasts are used in the production of different kinds of alcoholic beverages. Beer, which is an un-distilled product of grain-mesh fermentation, is brought about by Saccharomyces cerevissiae and S. carisbergensis.

Wine, which in also an un-distilled product of fruit-juice fermentation, is brought about by Saccharomyces ellipsoidens. Distilled beverages are called ‘hard liquors’, since these contain higher percentage of alcohol. Whisky, brandy, rum, gin, fenny and vodka are the familiar distilled beverages and these are produced by distillation of the fermented broth.

B. Antibiotics:

These are chemical substances, which are produced by some microbes, and it can kill or retard the growth of other (disease causing) microbes. According to their mode of action it may be narrow spectrum & broad spectrum.

Most of the antibiotics are produced by three groups of microbes namely, bacteria, actinomycetales and fungi. Bacterial antibiotics are obtained from Bacillus and pseudomonas species, Actinomycetales mainly include Streptamyces, Nocardia, Micromonospora, Streptosporangium etc. Among the fungi, antibiotics are mainly produced from Penicillium, Cephalosporium and Aspergillus. Alexander Fleming discovered the antibiotic penicillin, which he named it after the mould, Penicllium notatum.

Fleming, Chain and Florey were awarded the Nobel prize in 1945, for the discovery of antibiotics. Antibiotics have greatly helped the humanity in combating deadly diseases including plague, whooping cough, diphtheria, leprosy etc. In fact, it is difficult to imagine a world today, without the antibiotics.

C. Organic Acids:

Microbes have also been employed for the commercial and industrial production of chemicals, such as organic acids, alcohols and enzymes. Lactic acid commercially produced from fermentable carbohydrates such as corn, potato starch, molasses and whey (the watery part separated from curd) by using Lactobacillus. Commercial acetic acid is produced by fermenting alcohol with the help of Acetobacter species. It is used in the preparation of vinegar (sour wine), pharmaceuticals, colouring agents and insecticides.

Citric acid is produced by fermenting carbohydrates, such as cane and beet molasses, with the help of Aspergillus niger. Citric acid used in medicines, dyeing, making ink and as flavouring and preservating agent. Cyelosporin-A, an important bioactive chemical, used as an immuno­suppressive agent in organ transplatation, is produced by the fungus, Trichoderma polysporum.

The blood cholesterol lowering agents, statins, are produced by yeast, Monaseus purpureus. Clostridium butylieum (a bacterium) produces butyric acid. Ethanol, an important source of alcohol, is produced by the yeast, Saccharomyces cervisieae.

D. Enzymes:

Enzymes are bio-catalysts which catalyze biological reactions. These are proteinous in nature and found to play important role in industries. Microbes produced adaptive enzymes, lipases are used in detergent formulations which are used in removing oily stains in dry-cleaning industries.

Proteases are used in textile industry for removing proteinaceous stains. Bottled fruit juices are clarified (made clearer) by the use of proteases and pectinases. Amylases are used for the removal of starch from woven cloth removal of food spots in dry cleaning, and also in brewing industry as a replacent of malt for starch hydrolysis.

Rennin is used in cheese-making. Lactases are used to convert lactose (milk sugar) into lactic acid. Streptokinase, produced by the bacterium streptococcus, is modified by genetic engineering, and then used as a ‘clot buster’ for removing blood clots from the blood vessels of patients, who have suffered from myocardial infarction.

E. Vitamins:

Vitamins are essential for the growth and metabolism of organisms. These are produced during the normal metabolism of microorganisms. Vitamin B₁₂ (cobalamine) and vitamin B₂ (Riboflavin) are synthesized biotechnologically. By employing the industrial strains of Propioni ‘bacteria and Pseudomonas vitamin B₁₂ is produced commercially.

The vitamins contained in the microbial cells are recovered by centrifugation and chemical methods. Vitamin B₂ is produced commercially by fermenting microbes such as Ashbya gossypii and Ermothecium ashbyii. This vitamin is essential for the growth and reproduction in animals, including humans.

Thing # 3. Microbes in Sewage Treatment:

The waste water, coming from factories, slums, restaurants, health sanitaries, municipalities and hotels, and residential areas containing organic wastes, refuse, human faecal matters, animal wastes, dissolved organic compounds, in organic salts and many pathogenic microbes including bacteria and viruses, is collectively termed sewage. These municipal waste waters are generated in cities and towns, and are carried away in sewars.

The microbes present in the sewage include bacteria (Streptococci, Lactobacilli, Clostridia, Coliforms etc.) micro fungi, microalgae and Protozoa, Sewage containing microbes, such as pathogenic bacteria, is the source of many water borne-disease like typhoid, dysentery amoebic dysentery, jaundice, etc.

Sewage Treatment:

Before sewage water is discharged into any natural water bodies like streams, rivers, lakes etc., it should be treated for the removal of organic wastes, pathogenic bacteria and inorganic salts. Municipal sewage treatment plants (STP) are used for sewage treatment before it is discharged into the river or sea. Treatment of sewage water in done by the heterotrophic microbes naturally present in the sewage.

This treatment is carried out in three main stages:

1. Primary treatment

2. Secondary treatment

3. Tertiary treatment

1. Primary Treatment:

This involves the removal of coarse and solid materials/particles through filtration and sedimentation. At first the sewage is diluted with water and passed through a series of filters to remove floating wastes like polythene bags. The filtered sewage is then passed into grit chamber, where coarse solid materials settle down by gravity.

Afterwards, the sewage is sent to a sedimentation tank, where the suspended particles are allowed to settle down. All solids that settle down constitute the primary sludge, and the supernatant forms the effluent. The effluent from the primary settling tank is taken for secondary treatment.

2. Secondary treatment or Biological treatment:

The primary affluent is passed into large aeration tanks, where it is constantly agitated, and then air is pumped into it to make it aerobic. This allows vigorous growth of useful microbes into ‘flocks’ (=masses of bacteria associated with fungal filaments to form mesh-like structures), which consume a major part of organic matter; as a result, the BOD (Biochemical Oxygen Demand) of the effluent is significantly reduced. This effluent is passed through a sedimentation tank and the microbial flocks allowed to settle down as sediment This sediment is known as ‘activated sludge.’

The aeration helps aerobic microbes (such as micro algae, micro fungi, bacteria and protozoa) to grow and oxidize the organic matters present in the effluent. The activated sluge is pumped into large tank called anerobic sludge digester. Here, anerobic microbes start digesting the bacteria and fungi in the sludge. During, digestion, bacteria produces a mixture of gases, such as methane, carbon dioxide and hydrogen sulphide. These gases constitute the ‘biogas’ which can be used as a source of energy, as it is inflammable.

3. Tertiary treatment:

The effluent from the secondary treatment plant is subjected to tertiary treatment for the removal of dissolved nutrients, and then generally released into natural water bodies like streams and rivers.

Thing # 4. Microbes in Energy Generation:

Biogas is a mixture of gases (mainly consisting of methane gas), produced by the microbial activity, which can be used as fuel. The bacteria involved in the production of biogas are collectively known as methanogens, which grow anaerobically on cellulose material and produce large amount of methane, along with carbon dioxide and hydrogen.

The most common anaerobic bacteria are methanogenic archaebacteria, represented by Methanobacterium. These bacteria are also present in the rumen (a part of the stomach) of cattle. The ‘cow-dung’ (faeces of cattle), commonly called ‘gobar’ is rich in these bacteria and the gas generated is called biogas which is used for cooking and lighting.

Characteristics of Bio Gas:

1. It is colourless, odourless mixture of gases.

2. It burns with a blue flame.

3. It does not release smoke while burning.

4. It contains methane, carbon dioxide, hydrogen sulphide, nitrogen, oxygen, hydrogen & carbon monoxide.

5. The energy content of 28m3 of gas is equal to 20.8 litres of petrol or 18.4 litre of Diesel.

Gobar Gas Plant:

The biogas producing plant if commonly known as gobar gas plant. In rural areas, biogas plants are built to produce biogas for domestic consumption. A biogas plant consists of a concrete tank (10-15 feet deep), provided with a floating lid. A slurry or a mixture of cow-dung and water (1: 1 ratio) is fed to the tank.

As the gas is released from the slurry, the floating lid keeps on rising; the gas is than allowed to pass through an outlet pipe. This pipe is connected to the supply line, from which the gas can be supplied to the houses. The leftover shurry is discharged through another outlet, which can be used as organic fertilizer.

The technology of biogas production was developed in India, mainly due to the efforts of Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC). Now it is a boon to rural people as an alternative source of energy.

Microbes as Bio-control Agents:

Bio control refers to the use of biological methods for controlling plant diseases and pests. In modern society, these problems have been tackled by using toxic chemical substances called insecticides and pesticides.

These toxic chemicals are extremely harmful to humans his domestic animals and the environment, thus polluting environment (soil, water and air). Many chemical pesticides have carcinogenic effects; while some cause dermatitis and allergy.

In recent years, the biological control of pests and diseases is gaining importance. The bio control agents relies on natural predation, instead of the use of toxic chemicals. The use of bio control methods will certainly reduce the dependence on toxic chemical insecticides and pesticides. There has been considerable progress in controlling weeds, insects and pests by the use of bio pesticides.

Thing # 5. Microbes as Bio-pesticides:

Bio pesticides include pesticides of biological origin or the biological control agents.

These are used to control the weeds and insect pests: accordingly, these have been divided into two groups:

(a) Bioherbicides

(b) Bioinsectides

Bio herbicides include biological agents such as insects, fungi, bacteria, nematodes, parasitic plants etc., which are being employed to control weeds.

Some of the examples of bio herbicides are as follows:

(i) Phytophthora palmivora:

This herbicide controls the growth of milk-weed vines in citrus orchards.

(ii) Cochineal insect (Cactoblastic cactorum):

This herbivorous insect is introduced to cheek the growth of cacti in India and Australia.

(iii) Puccinia chondrilla:

This rust fungus is employed to control the skeleton weed (Chondrilla junced) in Australia

(iv) Alternaria eichhorniae:

This indigenous fungus is employed to control the aquatic weed water hyacinth (Eichhornea crassipes)

(v) Chrysolina beetles:

These are introduced to cheek the extensive growth of Klamath weed (Hypericum perforatum) in USA.

Bio insectides are being used in pest management, and these are non-toxic and pollution free and hence quality products could be made available for human consumption.

Some well known examples of bioinsectides are as follows:

(i) Ladybird beetles:

These serve as natural predators and regulate aphids.

(ii) Dragon flies:

These control mosquitoes

(iii) Trichoderma (fungus):

This acts a bio fungicide and control many soil borne diseases like root rot, rhizome rot, stem rot etc. It also inhibits pathogens through the release of toxic-like substance such as gliotoxin, viridin, gliovirin etc.

(iv) Agrobacterium radiobacter:

The crown gall disease of apple is caused by the virulent strain of Agrobacterium turefaciens. This disease has been successfully controlled by treating the seeds, seedlings and cuttings with a suspension of a nonpathogenic strain of Agrobacterium radiobacter (K-84).

(V) Baculoviruses:

These include two important genera, viz., Nucleopolyhedrovirus (NPV) and Granulovirus (GV), which occur naturally and found to be effective on some insects. These bio-insecticides are employed to control harmful insects such as ants, wasps, gnats and beetles, which feed on the foliage of crop plants. When these insect eat virus particles from Baculoviruses sprayed foliage, the granules get dissolved is the gut by the digestive juice, and the infected insects, die releasing more viruses on the leaf surface.

These are found to be harmless to non-target organisms, including beneficial insects, birds, mammals and plants. Thus baculoviruses are useful in integrated pest management (IPM) programme, where beneficial insects could be conserved, when ecologically sensitive area is being treated.

(vi) Bacillus thuringiensis (Bt.):

This bacterium contains some insecticidal proteins, such as thurioside. These protein toxins serve as stomach poisons and found to be highly insect specific, and when consumed by the target insect larvae (caterpillars), leads to their death. These toxins are known to be biodegradable and believed to be inactive against mammals and other animals. The dried spores of Bacillus thuringiensis are available in sachets and marked commercially.

These spores are mixed with water and sprayed on to the vulnerable plants such as fruit yielding plants, Sunflowers, Brassicas etc., when the virus particles are eaten by the insect larvae (caterpillars), the toxin is released in their guts, and the larvae are eventually killed.

Scientists have not only identified the genes for insectidal crystal(cry) proteins, but also isolated these genes from the bacteria and incorporated them into the genomes of various crop plants including cotton, tomato, potato, brinjal etc., by employing biotechnological methods (eg.: Bt brinjal).

Thing # 6. Microbes as Bio-fertilizers:

The carrier based microbial inoculants being added to the soil to enrich the soil fertility are called Bio fertilizer it is also known as microbial fertilizer or microbial inoculants. The use of fertilizers improves the quality of soil, which is quite essential to increase the productivity of cultivated crops.

The traditional fertilizers consist of materials of biological origin, which are added into the soil to improve and maintain its fertility. The traditional fertilizers are composed of manures, which are partially decomposed organic materials, containing almost all the essential nutrients required by the plants. The manures are broadly grouped under three categories, namely, farm yard manure, tor FYM) compost and green manure.

The farm yard manure is composed of dung of farm animals and their urine, farm refuse and crop residues, which are allowed to undergo partial decomposition, with the help of soil microbes. The residue of gobar gas plant is also a kind of farm yard manure. The microbes transform the complex organic debris into humus (a dark amorphous material), and the resultant degradation products are easily assimilated by plants.

The compost is a kind of manure which is prepared by decomposing the dung of farm animals and crop residues in specially designed ‘gobarpits’. In about 6 to 8 months, the partial degradation will be completed and the compost will be ready to use.

The green manures are prepared from green plants, mainly consisting of several species of leguminous and non-leguminous plants grown in the corners of the fields. The following species of plants are commonly used in the preparation of green manures: Crotalaria juncea (sunn hemp), Gliricidia maculata (leafy manure), Sesbania aculeritec (Dhaincha), Lens esculenta (Lenticel), Macrotyloma uniflorum (Horse-gram), Cassia torn (Thajanku) etc. These leafy manures are added to the soil while these are still young and green. This enriches the soil by releasing nitrogen, phosphorus, calcium, sulphur and other mineral contents.

In recent years, the use of chemical fertilizers to meet the ever increasing demands of agricultural produce has significantly contributed to the soil and water pollution. To counter this, lately, there has been tremendous pressure on farmers to use bio fertilizers and practice organic farming.

Earthworms, popularly known as ‘friends of the farmers’, play an important role in the development and maintenance of soil fertility. Earthworms are being employed to produce “vermicompost”, which contains both macro and micronutrients essential for plants. Besides, ‘vermicompost’ is eco-friendly, harmless, and can be safely added to the soil to improve the fertility of soil. Vermicompost is supplied to farmers in sachets.

Bio fertilizers include basically microorganisms, such as bacteria, fungi, and cyanobacteria, which enrich the nutrient quality of the soil. Some specific microorganisms are cultivated scientifically in laboratories, and then supplied to the farmers in sachets, so that these can be utilized in the agricultural fields.

Some of the more important bio fertilizers are listed as follows:

(a) Microphos Bio-fertilizers:

The main microbes are bacteria (Pseudomonas striata and Bacillus polymyxa) and fungi (Aspergillus sp.). These solubilize bound phosphate of rock and soil to increase the availability of soluble phosphates to plants.

(b) Rhizobial Bio-fertilizers:

The bacterium, Rhizobium, occurs freely in the, soil, but these cannot fix nitrogen in the free state. It can lead a symbiotic life with leguminous plants, and can fix up to 500 kg nitrogen per hectare. These bacteria enter into the roots of leguminous plants and form root nodules. The specific strains of Rhizobia are used as seed inoculants, and the seeds are coated with Rhizobium culture before sowing. The soil is also inoculated during the sowing season. The cultured Rhizobiutn is supplied in polythene packets and supplied to the farmers.

(c) Nitrogen Fixing Bacteria:

Azotobacter is the most popular free-living nitrogen fixing bacteria, which can fix atmospheric nitrogen in the soil and make it available to the plants. This bio fertilizer is available under the brand name ‘azotobacterin’, which is being used in many east European countries. Many crop plants, such as wheat, maize, barley, cabbage, carrot etc., have been found to yield up to 20 percent increase in crops, by the application of this fertilizer.

Some species of bacteria enter into loose association with the roots of cereals and grasses to fix nitrogen. This kind of association is referred to as associative symbiosis. Azospirillum lipoferum (or Spirillum lipoferum) lives in close contact with the roots of maize and brazilian grasses, and fix nitrogen.

(d) Cyanobacterial Bio-fertilizers:

The use of Cyanobacteria (or Blue-green algae or BGA) as a source of biofertiliser, is quite successful in paddy fields. Anabaena, anabaenopsis, nostoc, scytonema, cylindrospermum, fischerella, stigonema etc., are some of the more common nitrogen fixing cyanobacteria. The soil condition of paddy fields provides the ideal environment for the growth of nitrogen fixing cyanobacteria. Under normal environmental conditions, the use of cyanobacteria can produce upto 30 kg of biologically fixed nitrogen per hectare.

Farmers can prepare cyanobacterial biofertilizers in their own paddy fields by culturing the suitable strains in open tanks made of galvanized iron sheets or bricks and cement. The cultured algal mass is dried and mixed with suitable carriers and filled in polythene bags for future use. The dried flakes of this biofertiliser can be stored for 2 to 3 years. The powdered biofertiliser is sprayed in paddy fields at the rate of 10 kg per hectare.

Azolla-Anabaena symbiosis contributes bulk of the cyanobacterial biofertileser. Azolla is a small water fern with branched floating stem, having deeply bilobed leaves and true roots. The cyanobacteria, Anabaena azollae, grows as symbiont within the cavities of the aerial chlorophyllous leaves of Azolla.

Azolla grows profusely in paddy fields. It is inoculated with Anabaena azollae, about a month before rice transplantation. Using Azolla as biofertilizer, farmers were able to produce upto 50 percent higher paddy yield. Blue green algae also add organic matter to the soil and increase its fertility.

(e) Mycorrhiza:

The symbiotic association of fungi with the roots of plants is known as mycorrhiza. As a result of this association, the roots change their shapes and may become nodulated, tuberous or coralloid.

The mycorrhizae occur in two forms:

1. Ectomycorrhizae and

2. Endomycorrhizae.

In ectornycorrhiza or ectotrophic mycorriza, the fungal mycelium completely encloses the feeder rootlets forming sheath or mantle. The hyphae penetrate into the inter cellular spaces of the root cortex to form a network, called ‘Harting net’ The fungal hyphae increase the absorptive surface of the roots; as a result, higher intake of nutrients such as nitrogen, phosphorus, calcium and potassium, from the soil is made possible. Ectomycorrhiae are found in plants such as Eucalyptus, Pinus, Oaks etc.

In endomycorrhiza or endotrophic mycorrhiza, the fungus usually lives in the intercellular spaces and intracellularly in the cortical cells of roots. This kind of association is found in the roots of cereals, legumes, soya-bean, tobacco, rubber, tea, citrus and also in many orchids. Endomycorrhizae arc quite useful for the absorption of phosphorus, sulphur, potassium, copper, zinc etc. by roots.

Thus, the use of biofertilisers in agriculture has great advantages. These not only improve the physical and chemical properties of the soil; but also enhance the crop yield economically, sustaining soil fertility without causing atmospheric pollution.