Microbes in Human Welfare

Wine and beer are traditional alcoholic beverages produced without distillation of the fermented broth, whereas whisky, brandy, and rum are concentrated by distillation.

Streptokinase produced by Streptococcus and modified by genetic engineering is used as a 'clot buster' to remove intravascular blood clots in myocardial infarction patients.

Reference: NCERT Class XII, page 153.

$Saccharomyces\ cerevisiae$ is commonly called brewer's yeast. It causes fermentation of carbohydrates, producing ethanol.

$Clostridium\ butylicum$ produces butyric acid by fermentation; it does not produce lipase. Lipase is produced by $Candida\ albicans$.

Aspergillus niger (a fungus) is used for the commercial production of citric acid.

Myocardial infarction is caused by a clot blocking a coronary blood vessel.
Streptokinase, produced by the bacterium Streptococcus and modified by genetic engineering, is used as a clot buster to remove the clot.
Statins lower blood cholesterol, penicillin is an antibiotic and cyclosporin-A is an immunosuppressant.

Statins produced by the yeast Monascus purpureus are used as blood-cholesterol lowering agents.
They act by competitively inhibiting the enzyme responsible for the synthesis of cholesterol.
Ethanol comes from Saccharomyces, streptokinase from Streptococcus and citric acid from Aspergillus niger.

Cyclosporin A, which is used as an immunosuppressive agent in organ-transplant patients, is produced by the fungus $Trichoderma\ polysporum$. This pair is correct.
$Monascus\ purpureus$ (a yeast) produces statins, which are blood-cholesterol lowering agents, not a drug for swine flu.
$Penicillium$ gives the antibiotic penicillin; the 'clot buster' used for heart patients, streptokinase, comes from the bacterium $Streptococcus$.
No AIDS drug is obtained from $Pseudomonas$.
Hence the correct option is organ-transplant and $Trichoderma$.

$Clostridium\ butylicum$ (a bacterium) produces butyric acid; lactic acid is produced by $Lactobacillus$. So this match is wrong.
$Aspergillus\ niger$ (a fungus) produces citric acid – correct.
The yeast $Monascus\ purpureus$ produces statins, the blood-cholesterol lowering agents – correct.
$Acetobacter\ aceti$ (a bacterium) produces acetic acid – correct.
Hence the wrong matching is $Clostridium\ butylicum$ – lactic acid.

The yeast $Saccharomyces\ cerevisiae$ (brewer's yeast) is used for the commercial production of ethanol by fermentation of malted cereals and fruit juices.
$Aspergillus\ niger$ is used for producing citric acid.
$Clostridium\ butylicum$ is used for producing butyric acid.
$Trichoderma\ polysporum$ is the source of cyclosporin A, an immunosuppressive agent.
Hence ethanol is commercially produced through a species of $Saccharomyces$.

Ethanol is produced by the fermentation of sugars by the yeast $Saccharomyces\ cerevisiae$.
Molasses is the thick, dark syrup left as a by-product of the sugar industry after the crystallisation of sugar from sugarcane juice.
It is rich in fermentable sugars (sucrose, glucose and fructose), is cheap and is available in large amounts, so it needs no prior conversion of starch into sugar.
Corn meal, soya meal and ground gram are rich in starch or protein and are costlier substrates.
Hence the most common substrate used in distilleries is molasses.

Amylases are used in the textile industry to remove starch (desizing) – correct.
Lipases are used in detergent formulations and help in removing oily stains from laundry – correct.
Pectinases (and proteases) are used to clarify bottled fruit juices – correct.
Alcohol is produced by the fermentation of sugars by yeast, through enzymes such as zymase; nitrogenase is the enzyme of nitrogen fixation and has nothing to do with alcohol production.
Hence the wrongly matched pair is alcohol – nitrogenase.

Vinegar (acetic acid) is produced by the acetic acid bacterium Acetobacter aceti, which oxidises ethanol to acetic acid.
Coliforms such as Escherichia coli are bacteria that live in the intestine of man and other warm-blooded animals. Their presence in drinking water indicates faecal contamination; they are not used for making vinegar.
So the pair coliforms - vinegar is wrongly matched.
Yeast (Saccharomyces cerevisiae) ferments sugars to produce ethanol.
Streptomycetes (species of Streptomyces) produce antibiotics such as streptomycin.
Methanogens (for example Methanobacterium) produce methane during the anaerobic breakdown of cattle dung, giving gobar gas (biogas).
These three pairs are correctly matched.

Curing is the process by which the characteristic flavour, colour and aroma of products such as tea, tobacco and coffee are developed.
The leaves are allowed to ferment under controlled conditions.
In tea, this fermentation is brought about by the activity of bacteria, for example Micrococcus candidans, which act on the substances present in the leaves.
Tobacco leaves are similarly cured by Bacillus megatherium.
Mycorrhiza is a symbiotic association of fungi with roots and has no role in curing, and viruses do not carry out fermentation.
So the curing of tea leaves is brought about by the activity of bacteria.

Starch is first hydrolysed to sugars (by amylase or acid). The yeast Saccharomyces cerevisiae then ferments the sugar into ethanol and $CO_2$: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
Penicillium gives penicillin, Azotobacter fixes nitrogen and Lactobacillus produces lactic acid.
So Saccharomyces is used to manufacture ethanol from starch.

Saccharomyces cerevisiae (baker's or brewer's yeast) ferments dough for bread and ferments malted cereals and fruit juices to produce ethanol for beverages such as beer.
Cheese and butter involve bacteria, citric acid comes from Aspergillus niger and lactic acid from Lactobacillus.

Trichoderma species are free-living fungi common in root ecosystems; they are effective biocontrol agents of several plant pathogens.
The lady bird beetle is an insect, not a microbe. Nucleopolyhedroviruses attack insects, not white rust (a fungal disease). Bt-cotton is a transgenic plant.

$Trichoderma$ species are free-living fungi that are very common in root ecosystems; they are effective biocontrol agents of several plant pathogens (i.e., of plant diseases).
Baculoviruses (genus $Nucleopolyhedrovirus$) are pathogens that attack insects and other arthropods; they control insect pests, not plant diseases.
$Bacillus\ thuringiensis$ is used to control butterfly caterpillars (insect pests).
$Glomus$ is a mycorrhizal fungus used as a biofertiliser.
Hence the common biocontrol agent for plant diseases is $Trichoderma$.

Biopesticides are biological agents used to control weeds, insects and pathogens.
$Bacillus\ thuringiensis$ produces the Bt toxin, which kills insect larvae (caterpillars); it is used as a bioinsecticide.
$Trichoderma$ species are free-living fungi that are effective biocontrol agents of several plant pathogens.
Nucleopolyhedrovirus (NPV), a baculovirus, is a species-specific, narrow-spectrum insecticide.
$Xanthomonas\ campestris$ is itself a plant pathogen, causing black rot of crucifers; it is not a biopesticide.
Hence $Xanthomonas\ campestris$ is not used as a biopesticide.

Trichoderma species are free-living fungi that are very common in the root ecosystems.
They are effective biocontrol agents of several plant pathogens.
Trichoderma harzianum grows over soil-borne pathogenic fungi (mycoparasitism), secretes enzymes such as chitinases and glucanases that dissolve their cell walls, and also produces antibiotics against them.
It is therefore used for the biological control of soil-borne plant pathogens such as Pythium, Rhizoctonia and Fusarium.
Gene transfer in higher plants is done with Agrobacterium tumefaciens, not Trichoderma.
So Trichoderma harzianum is useful for the biological control of soil-borne plant pathogens.

Azolla is a small aquatic fern. The cyanobacterium Anabaena azollae lives in cavities of its leaves and fixes atmospheric nitrogen.
Azolla is grown in rice fields as a biofertilizer.
Nostoc is a cyanobacterium (not a fern), Salvia is a flowering plant, and Salvinia is an aquatic fern that does not fix nitrogen.
So the aquatic fern that performs nitrogen fixation is Azolla.

Azolla, an aquatic fern, harbours the nitrogen-fixing cyanobacterium Anabaena azollae in its leaves.
Grown in paddy fields, it adds fixed nitrogen and organic matter to the soil, increasing the yield of rice.
So the aquatic fern used is Azolla.

Curd is more nourishing than milk. It has enriched vitamins, especially vitamin $B_{12}$.

Primary treatment is a physical process which involves sequential filtration and sedimentation, removing suspended solids.

BOD is the amount of oxygen needed by microorganisms to break down the organic matter in water.
A high BOD means a large amount of organic matter, i.e. the water is highly polluted.

In anaerobic sludge digesters bacteria digest the sludge and produce a mixture of gases: methane, hydrogen sulphide and carbon dioxide (biogas).

During anaerobic digestion of sludge, bacteria produce a mixture of methane, hydrogen sulphide and carbon dioxide (biogas).

BOD is the amount of oxygen that would be consumed if all the organic matter in one litre of water were oxidised by bacteria.
It measures the organic matter present in sewage water: the greater the BOD, the greater the polluting potential.

Primary treatment is a physical process: floating debris is removed by filtration and grit by sedimentation.
In secondary treatment the primary effluent is passed into aeration tanks, where aerobic microbes grow vigorously into flocs (masses of bacteria associated with fungal filaments).
These microbes consume the major part of the organic matter in the effluent, which greatly reduces its BOD.
The sludge is then digested by anaerobic bacteria in anaerobic sludge digesters, producing biogas.
Since the work is done by microorganisms, secondary treatment is called biological treatment.
Hence secondary sewage treatment is mainly a biological process.

The water fern Azolla harbours the cyanobacterium Anabaena azollae in its leaf cavities.
Anabaena fixes atmospheric nitrogen, so Azolla is used as a biofertiliser in paddy fields.
Frankia forms nodules on the roots of non-leguminous plants such as Alnus.

Many members of the genus Glomus form mycorrhiza, a symbiotic association of a fungus with the roots of plants.
The fungus absorbs phosphorus from the soil and passes it to the plant.
Azotobacter is a free-living nitrogen fixer and Trichoderma is a biocontrol agent.

Biofertilisers are organisms that enrich the nutrient quality of the soil; the main sources are bacteria, fungi and cyanobacteria.
$Rhizobium$ fixes atmospheric nitrogen in the root nodules of legumes.
$Nostoc$ (like $Anabaena$ and $Oscillatoria$) is a nitrogen-fixing cyanobacterium.
Mycorrhiza is the symbiotic association of a fungus with roots, which helps the plant to absorb phosphorus.
$Agrobacterium\ tumefaciens$ is a plant pathogen that causes crown gall tumours; it is used as a vector for gene transfer in plants and does not enrich the soil.
Hence $Agrobacterium$ is not a biofertiliser.

Many members of the fungal genus $Glomus$ form mycorrhiza, a symbiotic association with the roots of higher plants.
The fungal symbiont absorbs phosphorus from the soil and passes it to the plant.
Plants with such associations also show resistance to root-borne pathogens, tolerance to salinity and drought, and an overall increase in growth.
$Anabaena$, $Rhizobium$ and $Frankia$ are nitrogen fixers; they do not help in phosphorus absorption.
Hence $Glomus$ helps in the absorption of phosphorus.

Soyabean is a leguminous plant.
The roots of legumes form nodules by symbiotic association with the bacterium $Rhizobium$.
$Rhizobium$ fixes atmospheric nitrogen into organic forms in the nodules, which the plant uses as a nutrient; so it is used as the biofertiliser for legume crops.
$Azotobacter$ and $Azospirillum$ are free-living nitrogen fixers of the soil, and $Nostoc$ is a cyanobacterium used mainly in paddy fields.
Hence the biofertiliser used for raising a soyabean crop is $Rhizobium$.

Mycorrhiza is a symbiotic association between a fungus and the roots of a higher plant.
In endomycorrhiza the fungal hyphae penetrate the cortical cells of the root (vesicular-arbuscular mycorrhiza, VAM).
Many members of the genus $Glomus$ form such mycorrhiza; the fungus absorbs phosphorus from the soil and passes it to the plant.
$Nostoc$ is a cyanobacterium, $Agaricus$ is the mushroom (a basidiomycete) and $Rhizobium$ is a nitrogen-fixing bacterium.
Hence the example of endomycorrhiza is $Glomus$.

Organic farming uses biofertilisers and natural processes in place of chemical fertilisers.
$Glomus$ is a fungus that forms mycorrhiza and helps the plant to absorb phosphorus.
$Oscillatoria$ is a nitrogen-fixing cyanobacterium that adds organic matter and nitrogen to the soil.
Earthworms break down organic matter and are used to make vermicompost.
Snails are not used; they feed on crop plants and are pests.
Hence the snail is not used in organic farming.

Anabaena is a filamentous cyanobacterium with heterocysts, the cells in which nitrogen fixation takes place. It lives freely in water and soil.
Anabaena azollae lives symbiotically in the leaf cavities of the water fern Azolla. The Azolla–Anabaena association is used as a biofertilizer in rice fields, as it adds nitrogen to the soil.
Nostoc and Tolypothrix are also nitrogen-fixing cyanobacteria, but the partner of Azolla is Anabaena. Chlorella is a green alga, not a cyanobacterium, and does not fix nitrogen.
So the cyanobacterium is Anabaena.

Biofertilizers are organisms that enrich the soil with nutrients.
Blue-green algae (cyanobacteria) such as Anabaena, Nostoc and Oscillatoria fix atmospheric nitrogen in paddy fields.
Azolla, a water fern, has the nitrogen-fixing cyanobacterium Anabaena azollae in its leaves and is used as a biofertilizer in rice fields.
Legumes and grasses are crop plants, and Salmonella and E. coli are not biofertilizers.
So Azolla and BGA are a true pair of biofertilizers.

Gobar gas (biogas) is produced when methanogens such as $Methanobacterium$ act anaerobically on cattle dung.
Biogas is a mixture of gases: methane (about 50–70%), carbon dioxide (about 30–40%) and traces of $H_2$ and $H_2S$.
So the gas present in the largest amount is methane, which is also the component that burns.
Butane and propane are constituents of LPG, not of gobar gas.
Hence the maximum amount is that of methane.

During sewage treatment, the activated sludge is pumped into anaerobic sludge digesters.
Here anaerobic bacteria (methanogens) digest the bacteria and fungi of the sludge and produce a mixture of gases: methane, hydrogen sulphide and carbon dioxide (biogas).
Methane is the main component; it is also called marsh gas because it is produced in the same way in marshes.
Laughing gas is nitrous oxide ($N_2O$), propane is a petroleum gas and mustard gas is a synthetic chemical warfare agent; none is formed in this way.
Hence marsh gas is mainly produced.

Gobar gas (biogas) is produced when cattle dung and other organic waste are decomposed anaerobically by methanogenic bacteria (e.g. Methanobacterium) in a biogas plant.
Biogas consists mainly of methane ($CH_4$, about 50–70 percent), with carbon dioxide and small amounts of hydrogen sulphide and hydrogen.
Methane is inflammable and is used as a fuel for cooking and lighting. The spent slurry is used as manure.
So the major component of gobar gas is methane.

In a gobar gas (biogas) plant, cattle dung is digested anaerobically by bacteria.
In the final stage, methanogenic bacteria (methanogens) such as Methanobacterium convert the products into methane ($CH_4$), the main fuel gas of biogas, along with $CO_2$.
Methanogens are also present in the rumen of cattle, so dung is rich in them.
So methanogens are utilised in the gobar gas plant.

Organic farming is a cyclical, zero-waste method of farming in which the waste products of one process are cycled in as nutrients for other processes.
It uses only naturally produced inputs such as compost, manure, biofertilisers and biological pest control, so (B) is correct.
It avoids chemical inputs: no synthetic pesticides and no chemical fertilisers such as urea, so (C) is correct.
Genetically modified crops such as Bt cotton are not part of organic farming, so (A) is wrong.
Organic farming is defined by the way the crop is grown; it does not by itself make vegetables richer in vitamins and minerals (that is biofortification), so (D) is wrong.
Hence the correct statements are (B) and (C) only.

Probiotics are live micro-organisms which, when taken in adequate amounts, give a health benefit to the host.
They include species of Lactobacillus and Bifidobacterium and some yeasts.
They are taken as a live microbial food supplement, for example in curd, yoghurt and other fermented milk products.
On ingestion they beneficially affect the host by improving the balance of the intestinal microflora and checking the growth of disease-causing microbes.
They are not antibiotics (which are chemicals that kill microbes), not allergens and not cancer-inducing microbes.
So probiotics are live microbial food supplements.

Dough for bread or idli contains yeast (Saccharomyces cerevisiae) or bacteria.
In warm conditions these microbes ferment the sugars in the dough anaerobically, producing ethyl alcohol and carbon dioxide:
$C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
The $CO_2$ gas gets trapped in the dough as bubbles, making it rise and become soft and spongy. Warm weather speeds up the activity of the microbes.
The $CO_2$ is produced inside the dough, not absorbed from the atmosphere.
So the dough becomes soft and spongy because of fermentation.

Bread dough is mixed with baker's yeast, Saccharomyces cerevisiae.
The yeast ferments the sugars in the dough, producing ethanol and carbon dioxide: $C_6H_{12}O_6 \rightarrow 2C_2H_5OH + 2CO_2$
The $CO_2$ gas forms bubbles that make the dough rise; on baking, the bread becomes soft and porous (spongy), and the alcohol evaporates.
So bread becomes porous due to $CO_2$ released by the action of yeast.

Vitamin $B_{12}$ (cyanocobalamin, a cobalt-containing vitamin) is made only by microorganisms. Animals get it from food and store it mainly in the liver.
Liver (e.g. goat's liver) is the richest animal source of vitamin $B_{12}$.
Spirulina, a cyanobacterium used as single cell protein, is also rich in protein, minerals and vitamins including $B_{12}$ (in the form of related cobalamin compounds).
Plant foods such as chocolate, green gram, rice and carrot contain little or no vitamin $B_{12}$; egg and chicken contain only moderate amounts.
Its deficiency causes pernicious anaemia.
So the richest sources are goat's liver and Spirulina.

Spirulina, a cyanobacterium, is grown as single cell protein (SCP), a rich source of protein; correctly matched.
Rhizobium fixes nitrogen in the root nodules of legumes and is used as a biofertilizer; correctly matched.
Streptomyces species produce many antibiotics such as streptomycin, tetracycline and chloramphenicol; correctly matched.
Serratia marcescens is a bacterium known for its red pigment and as a cause of hospital infections; it has no connection with drug addiction.
So the pair that is not correctly matched is Serratia – drug addiction.

Selman Waksman, who discovered streptomycin from Streptomyces griseus (Nobel Prize 1952), coined the term 'antibiotic' in 1942 for chemical substances produced by microbes that kill or inhibit the growth of other microbes.
Alexander Fleming discovered the first antibiotic, penicillin (1928), but did not coin the term. Edward Jenner developed the smallpox vaccine, and Louis Pasteur developed vaccines and disproved spontaneous generation.
So the term antibiotic was coined by Selman Waksman.