Microbes in household products


Dairy Products :

Lactic acid bacteria (LAB) like Lactobacillus are added to milk. It converts lactose sugar of milk into lactic acid.

Milk can be changed into curd, yoghurt and cheese. The starter used in preparation of milk products actually contains millions of LAB.

(a) Curd : Indian curd is prepared by inoculating cream and skimmed milk with Lactobacillus acidophilus at a temperature of about 40°C or less. Curd is more nutritious than milk as it contains a number of vitamins, especially Vit B12 and organic acids.

(b) Yoghurt : It is produced by curdling milk with the help of Streptococcus thermophilus and Lactobacillus bulgaricus. It has a flavour of lactic acid and acetaldehyde.

(c) Butter milk : It is acidulated product which is formed by inoculating skimmed milk with starter culture of Streptococcus cremoris, S. lactis, Lactobacillus acidophilus, Leuconostoc species at 22°C for 18 hours.

(d) Sour Cream : It is inoculated with Streptococcus lactis for producing lactic acid and Leuconostoc cremoris for imparting the characteristic flavour.

(e) Cheese : It is partially degraded concentrate of milk fat and casein, manufactured by activity of microorganisms. There are several hundred varieties of cheese which are prepared by selected types of microorganisms. The quality and characteristic taste of cheese is determined by the biochemical activities of specific microorganisms. Cheese consists of milk curd that has separated from whey or liquid part. Cheese is of three types - soft (50-80% water), semihard (about 45% water) and hard (less than 40% water). The method of preparing cheese with the help of microbes was known in Asia and Europe long before Christ. Large holed Swiss cheese is ripened with the help of CO2 producing bacterium called Propionibacterium sharmanii. Roquefort cheese or blue cheese uses Penicillium roquefortii, while Camembert cheese employs Penicillium camembertii for ripening.

Bread :

Selected strains of Saccharomyces cerevisiae (Baker's yeast) grown on molasses are used for this purpose.

The kneaded flour is kept at a warm temperature for a few hours. It swells up. The phenomenon is called leavening.

Leavening is caused by secretion of three types of enzymes by yeast. They are amylase, maltase and zymase.

The leavened dough is baked. Both carbon dioxide and ethyl alcohol evaporates, making the bread porous and soft.

Dosa, Uppma and Idli :

These are fermented preparations of rice and black gram. The two are allowed to ferment for 3-12 hours with Leuconostoc and Streptococcus species of bacteria.

Other Foods :

Tempeh (Indonesia) Tofu (Japanese) and Sufu (Chinese) are fermented foods obtained from soya sauce, is brown flavoured salty sauce fermented from soyabean and wheat.

Tender bamboo shoots can be used as vegetable directly as well as after fermentation. Several types of sausages are prepared by fermentation and curing of fish and meat.

Toddy (Toddy palm-Caryota urens) :

The unopened spadices of palm are tapped to obtain toddy. It is a refreshing drink which can be heated to produce jaggery or palm sugar. Toddy left for a few hours undergoes fermentation with the help of naturally occurring yeast to form beverage containing about 6% alcohol.

Microbes in industrial products


Fermentive activity of microbes is used industrially to obtain a number of products. Production on an industrial scale, requires growing microbes in very large vessels called fermentors. The two common ones are alcoholic fermentation and antibiotics.

Fermented Beverages/Alcoholic Fermentation

Yeast species used in alcoholic fermentation are Saccharomyces cerevisiae (Brewer's Yeast), S. ellipsoidens (Wine Yeast), S. sake (Sake Yeast) and S. pireformis (Ginger Beer/Ale Yeast).

The nutrient medium is barley malt for beer, fermented rye malt for gin, fermented rice for sake, cashew-apple for fenny, potato for vodka, fermented cereals for whisky, fermented molasses for rum and fermented juices for wines and brandy.

Wine and beer are produced without distillation, whereas whisky (50% alcohol), brandy (65-70% alcohol), rum (40% alcohol) and gin about (40% alcohol) are produced by distillation of fermented broth.

Antibiotics (means against life in Greek)

An antibiotic is a substance produced by a microorganism, which in low concentration inhibits the growth and metabolic activity of pathogenic organisms without harming the host.

This is among the most significant discoveries of twentieth century.

First antibiotic is generally associated with the name of Alexander Flemming (1928) when he discovered Penicillin from Penicillium notatum.

The antibiotic was however, commercially extracted by efforts of Ernst Chain and Howard Florey. The chemical was extensively used in treating wounded American soldiers in world war II. Flemming, Chain and Florey were awarded Nobel Prize in 1945. Bulk of antibiotics are obtained from three groups of microorganism i.e., Eubacteria, actinomycetes and fungi.

Concept Builder

Name of the antibiotics :

1. From Eubacteria

(i) Bacitracin Bacillus licheniformis

(ii) Subtiiin Bacillus subtilis

(iii) Polymyxin Bacillus polymyxa

(iv) Gramicidin Bacillus brevis

2. From Actinomycetes

(i) Chlorotetracycline or aureomycin Streptomyces aureofaciens

(or tetracycline)

(ii) Chloramphenicol or chloromycetin Streptomyces venezuelae and S. lavendulae

(iii) Erythromycin Streptomyces erythreus

(iv) Neomycin Streptomyces fradiae

(v) Oxytetracycline or terramycin Streptomyces rimosus

(vi) Streptomycin Streptomyces griseus

Antibiotics have greatly improved our capacity to treat deadly diseases like plague, whooping cough, diphtheria, leprosy etc. So with reference to human beings these are pro-life.

Chemicals, Enzymes and Other Bioactive Molecules

Bioactive molecules are those molecules which are functional in living systems or can interact with their components. A number of them are obtained from microbes like organic acids, enzymes, cyclosporin A and statins.

(A) Organic Acids

Certain microbes have the ability to convert carbohydrates into organic acids, this capability of microorganisms is applied in the industrial production of some commercially important organic acids. A few very important organic acids are as follows.

1. Acetic acid : It is prepared from fermented alcohols with the help of acetic acid bacteria, Acetobacter aceti. Alcoholic fermentation by yeast is anaerobic process, but the conversion of alcohol to acetic acid is aerobic one. It is used for the prepration of vinegar. It is also used in pharmaceuticals, colouring agents, insecticides and plastic industries.

2. Citric acid : It is obtained through the fermentation carried out by fungi Aspergillus niger and Mucor species on sugary syrups. Yeast Candida lipolytica can also be employed, provided its nutrient medium is made deficient of iron and manganese. Citric acid is employed in dyeing, engraving, medicines, inks, flavouring and preservation of food and candies.

3. Gluconic acid : The acid is prepared by the activity of Aspergillus niger and Penicillium chtysogenum. Gluconate is used widely as a source of calcium for infants, cows and lactating mothers.

4. Lactic acid : It was first acid to be produced by industrial fermentation. It is commercially produced from fermentable carbohydrates such as corn and potato starch, molasses and whey by using the bacteria - Lactobacillus bulgaricus and L. delbrueckii.

(B) Enzymes

Hardly 1.0-1.5% of the total known enzymes are employed in industry and medicine.

1. Pectinases : They are obtained from fungi grown on pectin containing medium. Examples are Aspergillus niget, Byssochlamys fulvo. They are used in enhancing juice extraction and clearing of juices.

2. Proteases : Proteases are obtained from Mortierella renispora, Aspergillus and Bacillus species, used in detergents to remove proteinaceous spots. Bottled juices are also clarified using proteases and pectinase.

3. Amylases : They degrade starch. Amylases are obtained from Aspergillus, Rhizopus and Bacillus species.

Amylases, glucoamylases and glucoisomerases are employed in conversion of corn starch into fructose rich corn syrup.

4. Streptokinase (Tissue Plasminogen Activator or TPA) : It is an enzyme obtained from the cultures of some haemolytic Streptococci. It has fibrinolytic effect, used to dissolve blood clots in heart patients.

(C) Cyclosporin A

It is an eleven membered cyclic oligopeptide obtained through fermentive activity of fungus Trichoderma polysporum.

It has antifungal and anti-inflammatory properties. It is used as an immunosuppressive agent in organ-transplant patients.

(D) Statins

They are products of fermentation activity of yeast Monascus purpureus which resemble mevalonate and is competitive inhibitor of -hydroxy--methylglutaryl CoA reductase or HMG COA reductase.

This competitively inhibits cholesterol synthesis. It is used as cholesterol lowering agent.

Microbes in sewage treatment


Sewage is collective noun used to represent municipal waste (both liquid and solid waste) generated in cities and towns which is carried off in sewerage.

It contains large amount of domestic water and waste including human and animal excreta, microbes and every things that enter sewerage system.

Sewage or municipal waste should not be passed into rivers, streams and other water bodies, because it not only contains human excreta and other organic wastes but a number of pathogenic microbes.

It is made less polluting by passing it through sewage treatment plants (STPs).

Treatment of waste water is done by the heterotrophic microbes naturally present in the sewage.

The various steps in sewage treatment are :

1. Primary Treatment :

It is a physical process of removal of large and small particles from sewage through sequential filtration and sedimentation.

Initially, floating debris is removed by sequential filtration, then the grit (soil and small pebbles) are removed by sedimentation.

The sewage is first shredded and churned. It is then passed through many screens or skimmers to remove large pieces of organic matter. The sewage is now passed into a large primary settling tank having a gentle slope.

Grit, sand and other heavy particles settle down.

All solids that undergo sedimentation and screened organic matter collectively constitute primary sludge.

Primary sludge can be used for preparing compost or manure directly. It can also be burnt.

The waste water (primary effluent) after removing the primary sludge contains fine organic matter. It is passed for secondary treatment.

2. Secondary Treatment or Biological Treatment :

It involves biological process of microbial degradation of organic matter.

There are three main methods use of oxidation tanks, trickling filter method and activated sludge method.

In activated sludge method the effluent from primary settling tank is passed into an aeration tank. It is agitated mechanically.

Air is pumped into the effluent. It contains a large population of aerobic heterotrophic microbes, including bacteria and fungi.

The microbes form flocs (masses of bacteria associated with fungal filaments).

The BOD of the effluent rises initially and the treatment continues till the BOD decrease to a certain level.

It is taken to secondary settling tank where the flocs undergo sedimentation.

The sediment is called activated sludge (This can be the inoculant for next secondary treatment).

The supernatant is allowed to pass into rivers and streams.

Activated sludge is taken to anaerobic sludge digesters alongwith the primary sludge.

Here, anaerobic microbes act upon organic matter to first produce monomers and then organic acids.

This convert the latter into a mixture of gases like methane, hydrogen sulphide and carbon dioxide.

The gaseous mixture is called biogas. It is inflammable and can be used as a source of energy.

The spent sludge is used as manure, land fill or can be burnt. Pathogens present in the original sewage get killed during anaerobic digestion.

3. Tertiary Treatment :

It is physiochemical process in which chlorine gas, zirconium, ozone gas, perchlorate salts, UV rays or reverse osmosis etc are used to remove DDT, pesticides, pathogens and remove turbidity in waste water. It is preferred when water is to be used for domestic use.

River Action Plans :

Prior to 1985, very few cities and towns had sewage treatment plants.

The municipal waste water was discharged directly into rivers resulting in their pollution and high incidence of water borne diseases.

In order to protect the major rivers of India from sewage pollution, the Ministry of Environment and Forests, has initiated development of sewage treatment plants under the National River Conservation Authority, e.g., Ganga Action Plan (GAP), Yamuna Action Plan, etc.

Microbes in production of biogas


Biogas is a mixture of gases produced from degradable organic matter by activity of various anaerobic bacteria.

The microorganisms involved in biogas production are mainly facultative as well as strict anaerobic bacteria.

The most important among them are methanogenic archaebacteria, represented by Methanobacterium.

The other bacteria involved are Bacillus, Cellulomonas, Clostridium and Ruminococcus.

These bacteria are commonly found in anaerobic sludge formed during sewage treatment. Methanogens do occur in rumen of cattle where they act upon cellulose.

Composition of biogas :

The major component of biogas is methane (about 50 —70%) which is highly inflammable. The other gases are carbon dioxide (30 — 40%) and 10% mixture of other gases, viz., H2, H2S etc. Calorific value of biogas is 4429 kcal/m3 at 50% methane content.

Substrates Useful in Biogas Production :

Commercial Production of Biogas :

The technology for biogas production was developed in India by IARI (Indian Agriculture Research Institute) and KVIC (Khadi and Village Industries Commission).

A biogas plant has a large (10-15 ft. deep) concrete or brick lined air tight cylindrical tank called digester.

It has a charge pit for passage of slurry into digester, a floating gas holder of metal with an outlet for gas and a pit for removal of sludge or manure. The raw material used in biogas plants is cattle dung, night soil, farm refuse, water weeds (e.g., Eichhornia) and other organic wastes.

It is converted into slurry with 90% water content and fed to digester.

Cattle dung contains Methanobacterium and other methanogens which are normally present in rumen of cattle for aiding in digestion of cellulose.

An inoculum can also be provided when a gobar gas plant is to be initiated.

Formation of biogas is a three step anaerobic process :

1. Solubilisation (Decomposition) :

Organic wastes are composed of lipids, proteins, cellulose, hemicellulose and lignin. In the first stage of biogas generation, facultative anaerobic decomposers are active.

They secrete hydrolytic enzymes, e.g., lipases, cellulases, proteases, peptidases.

The enzymes breakdown the complex organic components into simpler and soluble substances. The latter are commonly called monomers.

2. Acidogenesis :

Monomers are changed into organic acids with the help of fermentating microbes. The most common organic acids produced during acidogenesis is acetic acid.

Hydrogen and carbon dioxide are produced as by products.

3. Methanogenesis :

Methanogens or methane producing bacteria become active.

They act on various components of microbial digestion and fermentation. Some important basic reactions are :

Microbes as biocontrol agents


Biological Pest Control or Biopesticide

1. Biopesticides are the organisms which are applied to destroy the pests. They are used to destroy the weeds as well as the insect pests. Two basic types are bioherbicides and bioinsecticides.

2. Transgenic plants are genetically engineered plants to develop resistance against pests. e.g., transgenic tobacco and transgenic cotton.

3. Smoother crops are those which do not allow the weeds to grow nearby e.g., barley, rye, Sorghum, millet, sunflower, alfalfa, soyabean, marigold etc. Smoother crops eliminate weeds through chemicals. Crop rotation with these crops will naturally reduce the incidence of weeds.

4. Catch/ trap crops : Around the major crop in the field some early growing crop is sown in strips which is termed as catch or trap crop. The pests get attracted towards the early grown trap crop and then can be easily killed by cutting and destroying the trap crop. A good example of trap crop is bhindi (okra) which is sown around the cotton field to attract the jassid and spotted bollworm. Sesame is also good trap crop to attract the red hairy caterpillar from the cotton field.

5. Bioherbicides : It involves the biological control of weeds by some living organisms. e.g., use of insects feeding on a specific weed or use of micro-organisms which will cause diseases in weeds. Some of the common examples are given below :

(a) In India and Australia, the overgrowth of Opuntia (prickly pear cactus) was checked by the introduction of the cochineal insect (Cactoblastis cactorum).

(b) The first bioherbicide was mycoherbicide called Devine, derived from a fungus Phytophthora palmivora which controls the growth of milk weed vines in Citrus orchards.

(c) Another mycoherbicide called Collego has been derived from conidia of fungus Colletotrichum gloeosporioides. It controls the growth of northern Jointvetch (Aeschynomene virginica fam. Leguminosae) growing in rice fields.

(d) Extensive growth of Hypericum perforatum or kalmath weed was checked in USA by the introduction of Chrysolina beetles.

(e) Water hyacinth has been successfully controlled in Florida using the indigenous fungus Cercospora rodmanii.

6. Bioinsecticides : These are non persistent, non toxic and biodegradable. They include

(a) Pathogens, parasite and predators :

A well known example of biological control of an insect pest is the destruction of large populations of aphids (a pest on crucifers) by an insect called lady bug or praying mantis which feeds on the aphids.

The hoover fly larvae (Syrphid larvae) are very effective in keeping the aphids (plant bugs) under check as they feed on the aphids only. Dragon flies are useful to get rid of aphids and mosquitoes.

The mosquito larvae are easily controlled by rearing the larvicidal fish Gambusia (mosquito fish).

The sugarcane scale insects are controlled by the coccinellid predators (Cailochorus negriti and Pharoscymnus homi), the fluted scale insect (lcerya purchasi), a common pest on Citrus trees by the lady bird beetles (Rodolia cardinalis) and Nephantis serinopa, is a dangerous pest on coconut palms, by Perisierola nephanticdis and Trichospilus pupivora.

Baculoviruses are pathogens that attack insects and other arthopods. NPV (Nuclearpolyhedrovirus) based insecticide has been found to eliminate bollworms which cause extensive damage to cotton. These are species specific and narrow spectrum.

Trichoderma species are effective biocontrol agents of several plant pathogens. Trichoderma species are free-living fungi that are very common in the root ecosystems.

(b) Sterilisation strategy : Screw worm (Cochliomyia hominivorax) was eradicated by releasing sterile males.

(c) Insect hormone or Pheromones :

The pheromones are those chemical messengers which help in communication, sending alarm signals, marking trails or for attracting males.

Pheromones are secreted by females. Traps containing pheromones are placed in infested
fields. Males attracted by the trap become unavailable for reproduction.

In confusion technique, the pheromone containing papers are spread all over the field, so
males can no longer locate the females.

Introduction of moulting hormone ecdysone or juvenile hormones at inappropriate times results in the early death of insect pests.

(d) Natural insecticide :

These are obtained from living organisms (Plants) e.g., rotenones (obtained from the roots of Derris elliptica), nicotine (obtained from tobacco), pyrethrum and cinerin (pyrethroids, obtained from Chrysanthemum cinerarifolium), azadirachtin from margosa (Azadirachta indica) leaves, thurioside from mutant strains of a bacterium called Bacillus thuringiensis (Bt).

Thurioside is a proteinaceous toxin and is effective against several insects such as moths, flies, mosquitoes and beetles which accumulate as crystals inside the bacteria during sporulation.

Integrated Pest Management (1PM)

Sustainable pest management is otherwise known as Integrated pest management i.e., integration of tactics for control of single pest on one or more crops.

The overall objective of IPM is to create and to maintain situations in which insects are prevented from causing significant damage to crops.

Microbes as a biofertilizers


Organic farming is the raising of unpolluted crops through the use of biofertilisers that provide optimum nutrients to crop plants.

Organisms which can be used to improve the nutrient quality of soil through biological activity are known as biofertilisers.

The main sources are bacteria, cyanobacteria and fungi. In paddy fields, cyanobacteria serve as an important biofertiliser.

(a) Symbiotic N2 fixing bacteria like Rhizobium leguminosarum fixes atmospheric N2 in root nodules of legumes.

(b) Frankia (Actinomycetes) in root nodules of non-legume plants (e.g., Casuarina and Alnus).

(c) Symbiotic cyanobacteria (blue green algae) like Anabaena azollae fixes atmospheric N2 in leaves of Azolla (water fern). Azolla pinnata (a pteridophyte) is used as an excellent fertilizer in rice field.

(d) Anabaena cycadae lives in coralloid root of Cycas (a gymnosperm).

(e) Aulosira is most active, non symbiotic nitrogen fixer in rice field in India.

(f) Free living nitrogen fixer like Azospirillum and Azotobacter enrich the nitrogen content in soil.

(g) Mycorrhiza : It is symbiotic association between the fungus and roots of higher plants (seed plants). Many members of the genus Glomus form mycorrhiza. The fungal partner absorbs phosphorus from soil and passes it to the plant. Plants having mycorrhizal associations show resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in growth and development. It is of two types :

(i) Ectomycorrhizae (Ectotrophic or Ectophytic) : Hyphae of fungus only form mantle on the outer surface of the root, increasing absorption of water and minerals e.g., Pinus, oak etc. Mycorrhiza absorb and store nitrogen, phosphorus, potassium and calcium.

(ii) Endomycorrhizae (Endotrophic or Endophytic) : Fungal hyphae penetrate into cortex and cells of root e.g., orchids, coffee and woody plants. These are also called as vesicular arbuscular mycorrhizae or VAM, because cortical cells swell and form vesicles or arbuscles. It has significant role in phosphorus nutrition in plants.