MICROBES IN HUMAN WELFARE
INTRODUCTION
- Microbes are microorganisms, which have a size of less than 0.1 mm.
- Microbes occur everywhere in air, soil, water, inside and outside bodies of other organisms, inside thermal vents or geysers (with a temperature of 100°C) etc.
- Microbes can be grown on artificial culture media where they form colonies, e.g., bacteria, fungi.
- During their metabolism, microbes produce chemicals, some of which have been in use by human beings since ages.
- A powerful industry based on microbes has been developed in recent time. A careful selection of microbial strains, improved method of extraction and purification of the products, have resulted in enormous yields.
- The use of living organisms in systems or processes for the manufacture of useful products may involve algae, bacteria, fungi, yeast, cells of higher plants & animals or subsystems of any of these or isolated components from living matter.
MICROBES IN HOUSEHOLD PRODUCTS
Microbes have played an important role in the preparation of household products.
CURD
- A common example is the production of curd from milk. Micro-organisms such as Lactobacillus and others commonly called lactic acid bacteria (LAB) grow in milk and convert it to curd. During growth, the LAB produce acids that coagulate and partially digest the milk proteins.
- A small amount of curd added to the fresh milk as inoculum or starter contain millions of LAB, which at suitable temperatures multiply, thus converting milk to curd, which also improves its nutritional quality by increasing vitamin B12. In our stomach too, the LAB play very beneficial role in checking disease causing microbes.
- For production of curds or yoghurt pasteurized milk is inoculated with a mixture of Streptococcus thermophilus and Lactobacillus bulgaricus and its lactose is fermented by keeping it at 40°C.
- The peculiar or characteristic taste and flavour of curds is due to presence of lactic acid and acetaldehyde.
- In India, curds are not generally commercially produced but in developed countries large scale manufacture of yoghurt is done. In U.S.A. alone about 75 lakh kilogram of yoghurt is manufactured every year.
DOUGH
- The dough, which is used for making foods such as dosa, idli, jalebi and bread is also fermented by bacteria. The puffed-up appearance of dough is due to the production of CO2 gas. Similarly the dough, which is used for making bread, is fermented using baker's yeast (Saccharomyces cerevisiae).
TODDY
- A number of traditional drinks (e.g. 'Todi' prepared from sap of palms) and foods are also made by fermentation by the microbes.
- Arrack is obtained by distillation of fermented toddy. If allowed to ferment for more than 24 hours, toddy becomes unpalatable as alcohol is changed to vinegar.
- Microbes are also used to ferment fish, soyabean and bamboo shoots to make foods.
CHEESE
- Cheese is partially degraded concentrate of milk fat and casein manufactured by the activity of microbes.
- Different varieties of cheese are known by their characteristic texture, flavour, taste and the specificity coming from the microbes used.
- For example, the large holes in 'Swiss cheese' are due to production of a large amount of CO2 by a bacterium named Propionibacterium shermanii. The 'Roquefort cheese' are ripened by growing a specific fungi on them, which gives them a particular flavour. Roquefort cheese employs Penicillium roqueforti for ripening.
MICROBES IN INDUSTRIAL PRODUCTS
- A variety of microbes are used to synthesize a number of industrial products valuable to human beings. e.g. - beverages and antibiotics.
- Industrial production requires the formation of large quantities of the product, which normally involves the microbial reactions to proceed in a specialized vessel called fermentor or bioreactor.
- There are two types of fermentation process - batch fermentation (or closed system) and continuous fermentation (or open system).
- Downstream processing is the name given to the stage after fermentation when the desired product is recovered and purified.
ALCOHOLIC FERMENTATION
- Louis Pasteur showed in the middle of nineteenth century that beer and butter milk are product of fermentation brought about by yeast. It is a microscopic single celled organism-Saccharomyces cerevisiae. Presently, however yeast for human and animal consumption is produced on commercial scale.
- Alcohol was the first product of ancient biotechnology.
- There are basically two types of yeasts –
- Baker's yeast
- Alcohol yeast or Brewer's yeast.
- Baker's yeast is generally utilized during the preparation of food materials to increase the taste of food, flavour in food and nutrients in food. It is grown on molasses. It is also utilized as leavening agent.
- By the incomplete degradation of complex organic compounds [sucrose] by yeast fermentation, alcohol is formed.
- Some other common products of yeast fermentation are
- Beer : It is produced from Hordeum vulgare (Barley) malt and alcohol content is 4-8%.
- Wine : It is produced from grapes, in which alcohol content is 10-20%.
- Brandy : It is produced by distillation of wine and alcohol content is 43-57%.
- Gin : It is produced from European rye-Secale cereale.
- Rum : It is produced from molasses of sugarcane and alcohol content is 40%.
NOTES
Another yeast which supplies nutritionally rich food for man and animals is Torulopsis utilis.
ENZYME
- The term 'enzyme' was coined by William Kuhne in 1876.
- Buchner (1897) found that living cells of yeast are not required for alcoholic fermentation, but their extract also causes fermentation. In dialysis process, small molecules are removed from enzymes.
- Enzymes are organic substances which enhance the rate of biochemical reactions (without undergoing any change themselves). Enzymes are also called biological catalysts or biocatalysts.
- Uses of Enzymes
- Detergents – proteases, α-amylases, cellulases and lipases.
- Leather industry.
- Wool industries.
- Glucose from cellulose.
- Food, dairy, juice and beverages industries.
- Production of glucose syrup.
- Total enzymes known are about 2,200 and only 1-1.5% are used.
RENNET
- Rennet is used in the manufacturing cheese.
PROTEASE
- This enzyme is obtained from Aspergillus oryzae and Bacillus subtilis.
- Bacillus licheniformis are utilized for the formation of detergents in the detergent industry (for removing proteinous strains on clothes). The bottle juices are clarified by the use of pectinases and proteases.
AMYLASE
- It works on starch and is used in beer, bread and textile industries.
It is obtained from Aspergillus oryzae, A. niger, Rhizopus oryzae, etc.
AMYLASE, GLUCOAMYLASE AND GLUCOISOMERASE
- By the action of all these enzymes, corn (maize) starch is transformed into fructose corn syrup. This syrup is sweeter than sucrose and used in the beverage industry to flavour soft drinks and in baking industry to sweeten biscuits and cakes.
TISSUE PLASMINOGEN ACTIVATOR (TPA) OR STREPTOKINASE
- This enzyme is utilized in the medicinal field.
- Streptokinase is produced by the bacterium Streptococcus and modified by genetic engineering.
- It is used as a clot buster for removing clots from the blood vessels of patients who have undergone myocardial infarction leading to heart attack.
THROMBIN
- It is obtained from beef plasma and is used for blood clotting in surgical operations.
PAPAIN
- Papain is a protein digesting enzyme which is obtained from latex of papaya.
- It is used for making meat tender.
PROTEIN MODIFYING ENZYMES
- Some enzymes are known to modify proteins for human use, e.g., conversion of pig insulin into human insulin called pseumcelin.
VITAMINS
- Vitamins are complex organic substances found in various food and required for specific metabolic reaction in cells.
- The term vitamin was first used by Funk who isolated
Vit-B1 for the first time. - Microbes are important commercial sources of several vitamins.
- The various vitamins include-
Riboflavin (Vitamin B2)
- If is found in cereals, vegetables and Brewer's yeast and was first produced in 1938. It is a crystalline, bitter, odourless, yellowish brown chemical and is essential for growth and reproduction in animals.
- The main sources of riboflavin are fungi- Ashbya gossypii and the yeast eremothecium ashybyii. By the use of original wild strain of mould Ashbya gossypi, production of Vit B2 increases 100-300 time more.
Cobalamin or Vitamin B12
- It was first isolated from liver extract in 1948.
- It is a compound which contains cobalt, and is now obtained in a cobalt rich substrate (e.g., corn, sugarcane, molasses or starch) by microbes such as Propionibacterium frendenreichii, Bacillus megaterium.
- Vitamin B12 is used to supplement animal feed, and in man for increasing appetite and for treating anaemia.
- By the use of mutant strains of Pseudomonas denitrificans production of Vit-B12 increases 50,000 times more.
Ascorbic Acid (Vitamin C)
- It is manufactured from L.sorbose which is commercially produced from D-sorbitol by biological dehydrogenation brought about by different species of Acetobacter.
ANTIBIOTICS
- The term antibiotic was coined by Selman Waksman (1942).
- An antibiotic is a substance produced by a micro-organism which in low concentration and inhibits the growth and metabolic activity of pathogenic organism without harming the host.
- Alexander Flemming was the first to produce an antibiotic (named penicillin) from Penicillium notatum.
- Waksman and Albert discovered streptomycin and Actinomycin. Burkholder isolated Chloromycetin.
- Antibiotics are of two types
- Broad spectrum antibiotic : It is an antibiotic which can kill or destroy a number of pathogens that belong to different groups with different structure and wall composition.
- Limited spectrum (specific) antibiotic : It is an antibiotic which is effective only against one type of pathogens.
- Action of Antibiotics : An antibiotic acts on pathogens by
- Disruption of wall synthesis.
- Disruption of plasmalemma repair and synthesis.
- (Inhibition of DNA/RNA/Protein synthesis.
- Antibiotics
- are harmless to host.
- are harmless to normal microflora of alimentary canal.
- have the ability to destroy pathogens as well as broad spectrum.
- are effective against all strains of pathogen.
- have quick action.
- Resistance to antibiotics Pathogens often develop resistance to existing antibiotics and thus, newer antibiotics are required to be produced.
The resistance is produced due to
- development of copious mucilage.
- alteration of cell membrane antibiotic cannot recognize the pathogen.
- change to L-form by pathogen.
- mutation in pathogen.
- Main sources of antibiotic production are of three types :-
- Eubacteriales – Most of this type of antibiotic is obtained from Bacillus sp (70%). Bacillus subtilis produces more than 60 antibiotics and Pseudomonas sp about 30%.
- Actinomycetales [Ramified] – Streptomyces, Micromonospora and Streptosporangium. From single species Streptomyces griseus more than 40 antibiotics have been obtained.
- Fungi – Penicillium.
Table : Antibiotic produced by microorganisms
STEROIDS
- They are complex crystallisable lipids having a tetracyclic hydrocarbon core (one 5-carbon and three 6 carbon rings) and a long side chain.
- They are constituents of hormones and some important biochemicals like cholesterol, progesterone, oestrogen, testosterone, cortisterone, and cortisone.
- Compounds of steroids are found in both animals and plants. The main important steroid which is found in animals is cholesterol. It is the main constituent of animal cell membrane and main point for the initiation of steroid in hormone inside the body.
- Steroids are used medicinally in correcting hormonal imbalance, anabolic stimulants, birth control pills, antifertility drugs, anti-inflammatories, relieving pain and suppressing immune responses.
- Various steroids differ from one another in radicals like
– OH, = O, – CO – CH3, – CO – CH2 – OH
- Murray and Peterson (1950) found that Rhizopus stolonifer could bring about hydroxylation required for steroid synthesis including removal of hydrogen [dehydrogenation] from specific carbons.
Different microorganisms produce different steroids from progesterone like pregnane, cortexolone, androsterone etc. The commercial conversion of cortexolone to Prednisolone which is used as anti-inflammatory drugs, involve first hydroxylation then dehydrogenation.
ORGANIC ACID
- Some organic acids are manufactured by employing fermentation activities of fungi and other bacteria. For e.g., Citric acid, vinegar, lactic acid etc.
- Citric acid : It is obtained by the aerobic fermentation of sucrose by the fungus Aspergillus niger. This acid is used in medicine, flavouring extracts, food and candies; the manufacture of ink, dyeing. It is also produced by yeast.
- Acetic acid or Vinegar : Vinegar production is a two step fermentation process :
- First step : Alcoholic fermentation of a carbohydrate into alcohol by yeast.
- Second step : Aerobic oxidation of alcohol into acetic acid by the bacterium Acetobacter aceti.
The vinegar is the product of microbial fermentation. It was recognized by Kutzing in 1837. In 1868, Pasteur discovered it to be a result of biological activity.
Vinegar is used in various ways in homes. It is used as a condiment and for preserving pickles, canned vegetables and fruits.
Medicinally, it has an important role in promoting digestion and in overcoming constipation.
- Lactic acid : It is produced by fermentation of corn starch, molasses, potatoes and whey by Lactobacillus bulgaricus and Streptococcus lactis. It is the first acid to be produced.
- Gluconic acid : It is produced from glucose by fungi like Aspergillus, Penicillium and Mucor.
- Fumaric acid : It is produced from sugar by activity of Rhizopus nigricans (Bread mould).
- Butyric acid : It is obtained by Clostridium butylicum.
INTERFERON
- Issac and Linderman observed that immunity due to the formation of special soluble substances, produced by viral infected cells. This small group of protein is named - interferons.
- Interferon are the proteins released by the cells in response to a viral infection which they help to combat. These interferon do not inactivate the virus, but they make the unattacked cells, less susceptible so they are prevented from the attack of virus. They also prevent the viruses from taking over the cellular machinery.
- Interferon proteins have proved to be effective in treating influenza and hepatitis, but their role in cancer treatment is doubtful.
- Interferon is produced by Charles Weismann through the E.coli strain produced by recombinant DNA technology.
- There are three major types of interferons :
- Interferon- α (INF-α, produced by leucocytes or white blood cells,)
- Interferon-β (INF-β, produced by fibroblasts), and
- Interferon-γ (INF-γ, produced by stimulated
T-lymphocyte cells, hence also called immune interferon.)
DEXTRINS
- It is a plasma expander having 6-10% solution of dextrins which is given in case of haemorrhage, shock and dehydration and plasma transfusion.
- Dextrins are soluble polyglycans or polymers of D-glucose.
- They are prepared either through partial hydrolysis of starch or partial polymerisation of simple sugars through microorganism Leuconostoc mesenteroides or enzyme dextran sucrase. The enzyme is more useful as dextran or dextrin of suitable molecular weight can be obtained more easily.
INSULIN
- It is a proteinaceous hormone having 51 amino acids arranged in two polypeptides A and B having 21 and 30, amino acids, respectively and joined by S-S disulphide bridges.
- Sir Edward Sharpy-Shafer (1916) was the first to note that diabetes of some persons was because of failure of some pancreatic cells to produce a substance called insulin.
- Banting and Best (1921) were the first to isolate insulin from dog’s pancreas and used it to cure diabetes in man.
- The source of insulin used for curing diabetes these days, is the pancreas of slaughtered cattle and pigs. Though this insulin is effective in controlling diabetes, it results in certain undesirable effects.
- The first genetically engineered insulin obtained by recombinant DNA technique with the help of E.coli was produced by the American firms, Eli-Lilly on July 5, 1983. It has been given the trade name humulin and has been approved for clinical use.
VACCINES
- Production of antibodies against antigens inside the body is the basis of immunity. Process of inoculation of vaccines is called vaccination. Scientific base of vaccination was established by Louis Pasteur.
- First vaccine, discovered by Edward Jenner is for smallpox.
- A vaccine contains either weakened or even killed-attenuation pathogens [serum suspension with virulence] which still have antigens to induce antibody production. All these vaccines are called first generation vaccines. They are produced by conventional technique.
- Recently new vaccines are produced (called second generation vaccines). These are produced by recombinant DNA technology (genetic engineering), e.g., Herpes virus and Hepatitis-B vaccines.
Latest vaccines produced synthetically or synthesized vaccines are called third generation vaccines.
- An ideal vaccine
- should not be tumorigenic or toxic or pathogenic, i.e., it should be safe.
- should have very low levels of side effects in normal individuals.
- should not cause problems in individuals with impaired immune system.
- should not spread either within the vaccinated individual or to other individuals (live vaccines).
- should not contaminate the environment.
- should be effective in producing long lasting humoral and cellular immunities.
- should be cheap so that it is generally affordable.
- so far, such an ideal vaccine has not been developed.
MICROBES IN SEWAGE TREATMENT
- Sewage is the waste and waste water produced by residential and commercial sources and discharged into sewers.
- Harmful effects of sewage are -
- It produces offensive odour.
- Sewage contains pathogens like virus, bacteria etc, which results in dissemination of water borne diseases caused by microorganisms.
- Due to the addition of sewage and waste, oxygen levels of water are depleted, which are reflected in terms of BOD (biological oxygen demand) values of water.
- The industrial and municipal wastewater are treated in sewage treatment plant (STP) prior to disposal in water bodies.
- Sewage treatment system involves the following stages -
- Primary treatment
- Secondary treatment.
- Primary treatment is a physical process of removal of large and small particles from sewage through sequential filtration and sedimentation. All solids that settle form the primary sludge and the supernatant forms the effluent. Primary sludge can be used for preparing compost or manure directly or used in the generation of biogas.
- Secondary treatment of the liquid effluent from the primary settling tank is a biological process which involves microbial degradation of organic matter. The primary effluent is passed into large aeration tanks where it is continuously agitated mechanically and air is pumped into it. This allows vigorous growth of useful aerobic microbes into flocs (masses of bacteria associated with fungal filaments to form mesh like structures). This considerably reduces BOD of the effluent. The greater the BOD of waste water, more is its polluting potential.
- Once the BOD of sewage is reduced the effluent is then passed into a settling tank where the bacterial flocs are allowed to sediment. This sediment is called activated sludge which is taken to anaerobic sludge digesters along with the primary sludge. Here, anaerobic microbes act upon organic matter of first produced monomers and then organic acids. Methanogens then convert the latter into a mixture of gases like methane, hydrogen sulphide and carbon dioxide.
- The effluent from the secondary treatment plant is generally released into natural water bodies like rivers and streams.
- The ministry of environment and forests has initiated Ganga action plan and Yamuna action plan to save these major rivers of our country from pollution.
MICROBES IN PRODUCTION OF BIOGAS
- Biogas is a gaseous fuel which is obtained by the anaerobic fermentation of animal wastes (like cattle dung, wastes, urine, faeces etc).
Table : Composition of biogas
- In rural areas of developing countries, it is a common practice to use animal dung for making dung cakes which are used for fuel. Thus, a potential fertilizer of the agricultural fields is wasted in burning.
The dung can be put to better use if it is used to generate biogas (gobar gas) and side by side a stabilised residue to serve as the fertiliser.
- The energy yield of biogas is lower than that of dung cakes but the efficiency of biogas burners is very high. Thus over all result indicates that production of biogas is more cost effective.
BIOGAS PLANT
- The biogas plant consists of a concrete tank (10-15 feet deep) in which bio-wastes are collected and a slurry of dung is fed. A floating cover is placed over the slurry, which keeps on rising as the gas is produced in the tank due to the microbial activity. The biogas plant has an outlet, which is connected to a pipe to supply biogas to nearby houses. The spent slurry is removed through another outlet and may be used as fertilizer.
Fig. A typical biogas plant
- Cattle dung is available in large quantities in rural areas where cattle are used for a variety of purposes. So biogas plants are more in rural areas. The biogas, thus, produced is used for cooking and lighting.
- 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 (KVlC).
- Biogas plant works based on the process called anaerobic digestion or fermentation of organic matter. Anaerobic fermentation of waste biomass can be visualised in three stages :
- The facultative anaerobic microbes degrade the complex polymers to simple monomers by enzymatic action. The polymers like cellulose, hemicellulose, proteins and lipids get degraded into monomers but lignins and inorganic salts are left as residue because they do not get degraded.
- In this the monomers are converted into organic acids by microbial action under partially aerobic conditions which are finally converted to acetic acid.
- In this the acetic acid is oxidized into methane by the activity of anaerobic methanogenic bacteria. These bacteria are commonly found in the anaerobic sludge during sewage treatment. These bacteria are also present in the rumen (a part of stomach) of cattle. A lot of cellulosic material present in the food of cattle is also present in the rumen. In rumen, these bacteria help in the breakdown of cellulose and play an important role in the nutrition of cattle. In this whole process digestion of cellulose takes place at a very slow rate so that it is the “rate limiting factor in biogas production”.
ADVANTAGE OF BIOGAS
- Biogas can be easily stored to provide a more efficient source of energy.
- It can be used for various purposes in addition to its use for cooking.
- One byproduct of this process is a stabilized residue which serves as a good fertilizer.
- It reduces the overgrowth of faecal pathogens because of non-availability of exposed waste. Thus, it is significant in improving sanitation.
- It also reduces the chances of spreading of pathogens in the field condition, minimising the incidence of diseases in a crop year after year.
- Its calorific value is about 23-28 MJ/m3.
PLANTS AS SOURCES OF HYDROCARBONS FOR PRODUCING PETROLEUM
- Melvin Calvin has identified certain plants which produce hydrocarbons. The plants of euphorbiaceae, asclepiadaceae and apocyanaceae produce latex (a milky secretion which contains hydrocarbons.)
- The liquid hydrocarbon of the latex can serve as the liquid fuel which can replace the fuel requirement of automobiles either mixed with petrol or as entire fuel. Plantation of such type of plants is called petro plantation. This is the such type of method in which source is available only through the demand.
- Alcohol as fuel
- Ethanol (C2H5OH) can be partly or wholly substituted for petrol in automobiles after suitable modifications in engines.
- Raising of crops like sugar beet, potato, maize, sugarcane, tapioca and molasses for producing ethanol is called energy cropping.
- Alcohol has been successfully used as motor fuel in Brazil and it is the first leading country in the world.
Table : Ways of utilizing biomass as fuel
MICROBES AS BIOCONTROL AGENTS AND BIOFERTILIZERS
- Biological control is the use of living organisms to control pests.
- Examples of biological control are -
- Bioherbicide : It control weeds. First bioherbicide was developed in 1961 and it was a mycoherbicide derived from a fungus Phytophthora palmivora which controls the growth of milkweed vines in citrus orchards.
- Ladybird and Dragonflies are useful to get rid of aphids and mosquitoes, respectively.
- Introduction of cochineal insect (Cactoblastis cactorum) to control of overgrowth of cacti.
- Baculovirus : These are pathogenic viruses, which infect and kill many insect pests and other arthropod pests. E.g. Nucleopolyhedro-virus. Baculoviruses are known to control pests like potato beetles, aphids and corn borers.
- Biofertilizers are organisms that enrich the nutrient quality of soil.
- Rhizobium and mycorrhiza serve as biofertilizers.
- Rhizobium is a symbiotic bacterium, which occurs in the root nodules of legumes. It fixes nitrogen (atmospheric) in presence of leghaemoglobin.
- Mycorrhiza refers to the symbiotic association between fungus and roots of higher plants.
- Azolla is a water fern which is an excellent biofertilizer for rice cultivation.
Study Notes for NEET/AIIMS/JIPMER
