Microbes in Human Welfare

Microbes In Household Products

Microorganisms, commonly known as microbes, are ubiquitous (found everywhere) and are involved in a wide range of activities. While some microbes are harmful and cause diseases, many are beneficial and play crucial roles in human welfare, from producing food products to managing waste and controlling pollution.

Many household products are produced with the help of microbes:

• Curd: Produced from milk by the action of bacteria, particularly Lactic Acid Bacteria (LAB) like Lactobacillus. LAB converts lactose sugar in milk into lactic acid, which coagulates and partially digests the milk proteins, forming curd. Curd also contains several vitamins (like Vitamin B12) and improves the nutritional value of milk.
• Yoghurt and Cheese: Produced by fermentation of milk using specific bacteria (lactic acid bacteria) and sometimes fungi. The type of microbes used and the processing methods determine the flavour and texture of different types of cheese.
• Dough for Dosa and Idli: The dough is fermented by bacteria, which produce $CO_2$ gas, causing the dough to rise (leavening). The fermentation also imparts a characteristic flavour.
• Bread: Made from dough fermented by baker's yeast (Saccharomyces cerevisiae). Yeast respires anaerobically (alcoholic fermentation), producing $CO_2$ gas, which makes the bread dough rise and gives bread its porous texture.
• Toddy: A traditional drink in some parts of South India, made by fermenting sap from palm trees using yeast.
• Fermented Fish, Soyabean, Bamboo Shoots: Microbes are used to ferment these food items in various traditional cuisines.

Microbes are also used in the preparation of other food products like pickles, sauerkraut, and fermented vegetables.

The use of microbes in food production is an ancient practice, leveraging their metabolic activities (fermentation) to transform raw materials, improve digestibility, enhance flavour, and sometimes increase nutritional value.

Microbes In Industrial Products

Microbes are widely used in industries to produce a variety of products on a large scale, including fermented beverages, antibiotics, chemicals, enzymes, and other bioactive molecules.

Industrial production involving microbes requires growing them in large vessels called fermentors (or bioreactors).

*(Image shows a diagram of a large fermentor with features like agitator, aeration system, temperature control, sampling port)*

Fermented Beverages

Microbes, particularly yeasts, are used for the fermentation of sugary substrates to produce alcoholic beverages.

• Brewer's yeast (Saccharomyces cerevisiae) is used for fermenting malted cereals and fruit juices to produce ethanol.
• Depending on the type of raw material and processing method (with or without distillation), different alcoholic beverages are produced:
  • Without distillation: Wine (from fruit juice), Beer (from malted cereals). These have lower alcohol content.
  • With distillation: Whisky, Brandy, Rum. Distillation concentrates the alcohol.

Antibiotics

Antibiotics are chemical substances produced by some microbes that can kill or retard the growth of other microbes (especially pathogenic bacteria). They are widely used to treat infectious diseases.

• The first antibiotic, Penicillin, was discovered serendipitously by Alexander Fleming in 1928 from the fungus Penicillium notatum. Its full potential as an effective antibiotic was later established by Ernest Chain and Howard Florey. (Fleming, Chain, and Florey were awarded the Nobel Prize in 1945).
• Antibiotics have revolutionised the treatment of bacterial infections and saved millions of lives (e.g., greatly improved treatment outcomes for diseases like plague, whooping cough, diphtheria, leprosy).
• Other antibiotics are produced from different microbes (e.g., Streptomycin from *Streptomyces* bacteria).

*(Image shows a petri dish with bacterial growth and a zone of inhibition around a Penicillium colony)*

Chemicals, Enzymes And Other Bioactive Molecules

Microbes are used in the industrial production of various organic acids, alcohols, enzymes, and other valuable molecules.

• Organic acids:
  • Citric acid: Produced by Aspergillus niger (a fungus).
  • Acetic acid: Produced by Acetobacter aceti (a bacterium).
  • Butyric acid: Produced by Clostridium butylicum (a bacterium).
  • Lactic acid: Produced by Lactobacillus (a bacterium).
• Alcohol: Ethanol is produced by fermentation of molasses or other sugary substrates by yeast (Saccharomyces cerevisiae).
• Enzymes: Microbes are a source of various industrial enzymes.
  • Lipases: Used in detergent formulations (remove oily stains).
  • Pectinases and Proteases: Used in clarifying bottled fruit juices.
  • Streptokinase: Produced by bacterium *Streptococcus*. Used as a 'clot buster' for removing blood clots from patients who have undergone myocardial infarction (heart attack). It is a recombinant produced enzyme.
• Bioactive Molecules:
  • Cyclosporin A: Produced by the fungus Trichoderma polysporum. Used as an immunosuppressant agent in organ transplant patients (to prevent rejection).
  • Statins: Produced by the yeast Monascus purpureus. Used as blood-cholesterol lowering agents. They act by competitively inhibiting the enzyme responsible for cholesterol synthesis.

Microbes are versatile biochemical factories, enabling the large-scale production of diverse substances valuable to human society, including pharmaceuticals, food additives, and industrial chemicals.

Microbes In Sewage Treatment

Sewage, or municipal wastewater, contains large amounts of organic matter, pathogens, and pollutants. Untreated sewage is a major source of water pollution and can cause various diseases. Sewage is treated in Sewage Treatment Plants (STPs) before it is discharged into natural water bodies. Microbes play a vital role in making sewage less polluting.

Sewage treatment involves two main stages:

1. Primary Treatment (Physical removal)
2. Secondary Treatment (Biological treatment)

Primary Treatment

• This stage involves the physical removal of large and small particles from sewage using screening and sedimentation.
• Screening: Floating debris (like plastic, rags) is removed by passing the sewage through screens.
• Grit removal: Grit (soil and small pebbles) is removed by sedimentation in settling tanks.
• The remaining liquid is called the primary effluent. The settled solids are called the primary sludge.
• Primary effluent is then transferred for secondary treatment. The primary sludge is sent for disposal (e.g., landfill or incineration).

Secondary Treatment Or Biological Treatment

• This stage involves the use of microbes to decompose the organic matter in the primary effluent. This significantly reduces the organic load and the Biological Oxygen Demand (BOD).
• Aeration tanks: The primary effluent is pumped into large aeration tanks, where it is continuously agitated mechanically and air is pumped into it. This provides oxygen to aerobic microbes.
• Formation of flocs: Aerobic bacteria grow rapidly and form masses associated with fungal filaments to form mesh-like structures called flocs. Flocs are masses of bacteria held together by slime and fungal filaments.
• Decomposition of organic matter: The microbes in the flocs consume the organic matter in the sewage as food, reducing the organic content of the effluent.
• Reduction in BOD: The BOD (Biological Oxygen Demand) is a measure of the amount of oxygen required by aerobic microorganisms to decompose the organic matter in a sample of water. As microbes in the aeration tank decompose organic matter, the BOD of the sewage is significantly reduced. A lower BOD indicates less pollution.
• Settling tanks: After aeration, the effluent is pumped into settling tanks. The flocs settle down as activated sludge.
• Activated sludge: A small part of the activated sludge is pumped back into the aeration tank to serve as inoculum (seed) for the next cycle of treatment. The remaining activated sludge is pumped into anaerobic sludge digesters.
• Anaerobic sludge digesters: In these tanks, anaerobic bacteria (anaerobic sludge digester bacteria) digest the activated sludge, producing biogas (a mixture of methane, hydrogen sulphide, $CO_2$). Biogas can be used as fuel.
• Secondary effluent: The liquid remaining after secondary treatment is called the secondary effluent. It has a significantly reduced BOD and is usually discharged into natural water bodies.

*(Image shows a diagram illustrating the stages of sewage treatment: raw sewage $\rightarrow$ primary settling $\rightarrow$ aeration tank $\rightarrow$ secondary settling (activated sludge) $\rightarrow$ anaerobic digestion $\rightarrow$ clean effluent)*

Microbes are indispensable for biological sewage treatment, playing a vital role in breaking down organic pollutants and reducing the environmental impact of wastewater discharge.

Microbes In Production Of Biogas

Biogas is a mixture of gases produced by the anaerobic digestion of organic matter by microbes. It is primarily composed of methane ($CH_4$) (about 50-75%), along with carbon dioxide ($CO_2$) and traces of other gases.

Biogas is produced in a biogas plant, a concrete tank where various organic wastes (like cow dung, plant residues, sewage) are fed. Anaerobic bacteria digest these wastes in the absence of oxygen.

The Process of Biogas Production:

Biogas production is a multi-step process involving different groups of anaerobic microbes:

1. Hydrolysis/Solubilisation: Complex organic compounds (carbohydrates, proteins, fats) in the waste are broken down into simpler soluble molecules (sugars, amino acids, fatty acids) by hydrolytic bacteria.
2. Acidogenesis: Simple soluble organic molecules are fermented by acidogenic bacteria into volatile fatty acids (e.g., acetic acid), alcohol, $H_2$, and $CO_2$.
3. Methanogenesis: Methanogenic bacteria (e.g., *Methanobacterium, Methanococcus*) convert the volatile fatty acids, $H_2$, and $CO_2$ into methane and $CO_2$. These bacteria are strictly anaerobic.

$ \text{Organic wastes} \xrightarrow{\text{Hydrolysis, Acidogenesis}} \text{Volatile fatty acids, } H_2, CO_2 \xrightarrow{\text{Methanogenesis}} CH_4 + CO_2 $

Biogas Plant Design:

• A typical biogas plant has a concrete tank (digester) with a fixed dome or a floating gas holder.
• Organic waste (slurry) is fed into the digester.
• Anaerobic digestion takes place, producing biogas, which collects above the slurry.
• A gas outlet is provided to draw off the biogas.
• The spent slurry (digested residue) can be removed and used as manure, as it is rich in nutrients.

*(Image shows a diagram of a biogas plant highlighting the inlet for slurry, digester tank, gas holder/dome, gas outlet, and outlet for spent slurry)*

Significance of Biogas:

• Provides a clean and renewable source of energy for cooking and lighting, especially in rural areas.
• Reduces reliance on traditional fuels like firewood and dung cakes, which cause deforestation and air pollution.
• Produces valuable organic manure (spent slurry).
• Helps in waste management and sanitation.
• Reduces greenhouse gas emissions (by capturing methane).

The technology of biogas production was developed in India through the efforts of the Indian Agricultural Research Institute (IARI) and Khadi and Village Industries Commission (KVIC).

Microbes As Biocontrol Agents

Biocontrol is the use of biological methods to control plant diseases and pests. Using microbes as biocontrol agents offers an environmentally friendly alternative to chemical pesticides, which can cause pollution and harm beneficial organisms.

Biological Control Of Pests And Diseases

• Biocontrol methods aim to manage pests and diseases using natural predators, parasites, or pathogens.
• Using microbes for pest and disease control is a part of organic farming and integrated pest management (IPM).

Examples of Microbes as Biocontrol Agents:

• Bacteria:
  • Bacillus thuringiensis (Bt): A bacterium that produces a protein toxin (Bt toxin) that is toxic to certain insects (e.g., lepidopterans, dipterans, coleopterans). Spores of Bt can be applied as a spray on plants. When ingested by insects, the toxin becomes active in their alkaline gut and kills them. Genes for Bt toxin have also been introduced into crop plants (e.g., Bt cotton) through genetic engineering, making the plants resistant to insect pests.
• Fungi:
  • Trichoderma: A genus of free-living fungi commonly found in soil and root ecosystems. They are effective biocontrol agents against several plant pathogens, particularly root-borne diseases. They suppress pathogens through competition and parasitism.
• Viruses:
  • Baculoviruses: Viruses that infect insects and other arthropods. They are species-specific and have narrow spectrum insecticidal applications. They do not harm non-target organisms (like plants, mammals, birds, fish) or beneficial insects. They are used in IPM programmes, especially in ecologically sensitive areas.

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Biocontrol in Organic Farming:

• Organic farming integrates biocontrol methods to manage pests and diseases. The approach is to develop a system where pests are not eradicated but managed at a manageable level within a diverse ecosystem.
• This involves understanding the interactions between different organisms in the field, including natural predators and parasites of pests.
• Example: Introducing ladybugs (beetles) to control aphids, using dragonflies to control mosquitoes, cultivating varieties that attract beneficial insects.

The use of microbes as biocontrol agents is a key strategy for reducing the reliance on chemical pesticides, promoting sustainable agriculture, and protecting the environment and human health.

Microbes As Biofertilisers

Biofertilisers are organisms that enrich the nutrient quality of the soil. They are living microbes that help in increasing soil fertility by fixing atmospheric nitrogen, solubilising phosphorus, or decomposing organic matter.

Biofertilisers are an eco-friendly alternative to chemical fertilisers, contributing to sustainable agriculture and reducing environmental pollution.

Types of Biofertilisers:

1. Bacteria:
   • Nitrogen-fixing bacteria: Convert atmospheric nitrogen ($N_2$) into usable forms (ammonia, nitrates).
     • Symbiotic nitrogen fixers: Rhizobium (lives in root nodules of leguminous plants, fixing nitrogen symbiotically).
     • Free-living nitrogen fixers: Azospirillum and Azotobacter (aerobic bacteria living freely in soil).
   • Phosphorus-solubilising bacteria: Convert insoluble phosphate compounds in soil into soluble forms accessible to plants.
2. Cyanobacteria (Blue-green algae):
   • Autotrophic, freshwater or terrestrial microbes.
   • Many are symbiotic nitrogen fixers (e.g., Anabaena, Nostoc - some have heterocysts for N$_2$ fixation).
   • They are important biofertilisers in paddy fields, where they fix atmospheric nitrogen and also add organic matter to the soil.
   • Symbiotic associations with other plants (e.g., *Anabaena* in the fern *Azolla*).
3. Fungi:
   • Mycorrhiza: Symbiotic association between fungi and the roots of higher plants. The fungal hyphae increase the surface area for absorption of phosphorus and other minerals from the soil and provide them to the plant. In return, the plant provides organic nutrients to the fungus.
   • Example: Genus Glomus forms ectomycorrhiza or endomycorrhiza.
   • Mycorrhizal association makes plants more resistant to root-borne pathogens and tolerant to salinity and drought.

*(Image shows illustrations of root nodules with Rhizobium, free-living bacteria, filamentous cyanobacteria with heterocysts, and fungal hyphae associated with plant roots (mycorrhiza))*

Advantages of Biofertilisers:

• Eco-friendly: Do not cause pollution compared to chemical fertilisers.
• Cost-effective: Cheaper than chemical fertilisers.
• Improve soil health and structure.
• Sustainable: Help in maintaining long-term soil fertility.
• Increase crop yield.

Biofertilisers are increasingly being used in agriculture as part of a move towards organic and sustainable farming practices, leveraging the beneficial roles of microbes in enhancing food production.