Often associated solely with disease and spoilage, microbes (or microorganisms) are, in fact, indispensable partners in human progress. These tiny, invisible life forms—including bacteria, fungi, yeast, algae, and protozoa—are the unsung heroes driving processes crucial to our survival and well-being. From the food on our tables to the clean water from our taps, microbes play a pivotal role. This article explores the diverse and profound applications of microbes in human welfare.
1. Microbes in Household Food Processing
Long before the science of microbiology was established, humans were harnessing the power of microbes to produce and preserve food. These traditional biotechnologies rely on controlled fermentation.
- Dairy Products:
- Curd/Yogurt: The bacterium Lactobacillus (Lactic Acid Bacteria or LAB) is added to warm milk. It ferments the lactose (milk sugar) into lactic acid. This acid coagulates milk proteins, giving yogurt its thick texture and tangy flavor, while also preventing the growth of spoilage-causing microbes.
- Cheese: The production involves two key microbial steps. First, LAB acidifies the milk. Then, specific fungi or bacteria are added to ripen the cheese, giving different varieties their unique characteristics. For example, Penicillium roqueforti gives Blue cheese its veins and sharp flavor, while Propionibacterium shermanii is responsible for the holes in Swiss cheese.
- Bread:
- The baker’s yeast, Saccharomyces cerevisiae, is the key agent. When added to dough, this fungus ferments sugars, producing carbon dioxide gas. The gas gets trapped within the gluten network of the dough, causing it to rise and become fluffy. The alcohol produced during fermentation evaporates during baking.
- Traditional Fermented Foods:
- Idli and Dosa: A batter of rice and black gram is fermented by LAB and yeasts, which produce gases that leaven the batter, making idlis soft and spongy.
- Sauerkraut, Kimchi, and Pickles: These are produced by the natural fermentation of vegetables (cabbage, radish, cucumber) by LAB present on them. The lactic acid acts as a natural preservative and imparts a sour taste.
- Soy Products (Soy Sauce, Tempeh): Molds like Aspergillus oryzae are used to ferment a mixture of soybeans and wheat to produce soy sauce. Tempeh is a fermented soybean cake bound together by the mycelium of the fungus Rhizopus oligosporus.
2. Microbes in Industrial Production
On an industrial scale, microbes are grown in large fermenters (bioreactors) to produce a vast array of valuable compounds.
- Antibiotics: The first and most famous example is Penicillin, discovered from the fungus Penicillium notatum. Today, numerous antibiotics are produced using microbes, such as Streptomycin (from Streptomyces griseus) and Tetracycline.
- Organic Acids:
- Citric Acid: Produced by the fungus Aspergillus niger. It is widely used in the food and beverage industry (soft drinks, candies) and in pharmaceuticals.
- Acetic Acid (Vinegar): Produced by the bacterial oxidation of ethanol by Acetobacter aceti.
- Vitamins: Vitamin B12 is produced industrially using bacteria like Pseudomonas denitrificans, and Vitamin B2 (Riboflavin) is produced by the fungus Ashbya gossypii.
- Enzymes:
- Amylases: Produced by fungi like Aspergillus and bacteria like Bacillus, they are used to hydrolyze starch in the food and textile industries.
- Pectinases and Proteases: Used for clarifying fruit juices and tenderizing meat, respectively.
- Lipases: Used in detergent formulations to remove oil stains from laundry.
3. Microbes in Sewage Treatment
The treatment of urban wastewater (sewage) is a critical process for public health and environmental protection, and it is fundamentally a microbiological process. It occurs in two main stages:
- Primary Treatment: This is a physical process involving the removal of large debris and the settling of suspended solid particles.
- Secondary Treatment (Biological Treatment): This is where microbes take center stage.
- The effluent is passed into large aeration tanks. Here, a diverse community of aerobic heterotrophic microbes—bacteria, fungi, and protozoa—is allowed to grow, forming flocs (masses of bacteria associated with fungal filaments).
- These microbes vigorously consume the organic matter in the effluent as food, digesting it and oxidizing it into carbon dioxide, water, and minerals. This significantly reduces the Biochemical Oxygen Demand (BOD), a measure of organic matter in the water.
- Once the BOD is reduced, the effluent is passed to settling tanks where the bacterial flocs are sedimented. This sediment is called activated sludge; a part is pumped back into the aeration tank to inoculate the next batch, and the rest is sent for anaerobic digestion.
- Anaerobic Digestion: The activated sludge is digested anaerobically by specific bacteria like Methanobacterium. These microbes produce a mixture of gases rich in methane (biogas), which can be used as a fuel. The treated water is then discharged into a natural water body.
4. Microbes in Energy Generation
Microbes are at the forefront of generating sustainable bioenergy.
- Biogas: As mentioned above, anaerobic bacteria break down animal dung (gobar) and other organic waste in a biogas plant. The resulting gas, which is 50-70% methane, is an excellent fuel for cooking and lighting, while the spent slurry is a rich manure.
- Bioethanol: Yeast (Saccharomyces cerevisiae) ferments sugars derived from sugarcane, corn, or cellulosic biomass to produce ethanol. This ethanol is blended with petrol to create a cleaner-burning fuel for vehicles.
- Biodiesel: Certain species of microalgae have a high lipid (oil) content. These oils can be extracted and chemically processed into biodiesel, offering a promising alternative to fossil fuels.
5. Microbes as Biocontrol Agents
Biocontrol refers to the use of biological methods for controlling plant diseases and pests, reducing our reliance on chemical pesticides.
- The bacterium Bacillus thuringiensis (Bt) is the most famous example. It produces protein crystals that are toxic to the larvae of specific insects (like caterpillars and mosquitoes). When the insect ingests these crystals, they are activated in its gut, causing paralysis and death. Bt genes have been incorporated into plants like cotton to create genetically modified Bt-cotton, which is resistant to bollworms.
- Fungal species like Trichoderma, used as a biocontrol agent, are free-living in root ecosystems. They are effective against several plant pathogens.
- Baculoviruses, particularly from the genus Nucleopolyhedrovirus, are pathogens that attack insects and other arthropods. They are excellent candidates for species-specific, narrow-spectrum insecticidal applications.
6. Microbes as Biofertilizers
Biofertilizers are preparations containing live or latent cells of efficient strains of microorganisms that help crop plants’ uptake of nutrients by their interactions in the rhizosphere.
- Nitrogen-Fixers: These bacteria can convert atmospheric nitrogen (N₂) into ammonia, a form usable by plants.
- Free-living: e.g., Azotobacter, Azospirillum.
- Symbiotic: Rhizobium forms root nodules in leguminous plants (e.g., peas, beans), where it fixes nitrogen in exchange for shelter and food from the plant.
- Cyanobacteria: e.g., Anabaena, Nostoc, are important in paddy fields, where they fix atmospheric nitrogen and also add organic matter to the soil.
- Mycorrhiza: This is a symbiotic association between fungi and the roots of higher plants. The fungal hyphae form a network that greatly increases the surface area for the absorption of water and minerals like phosphorus from the soil, which is transferred to the plant.
Conclusion
From the kitchen to the refinery, from the farm to the wastewater treatment plant, microbes are our silent, efficient partners. The field of microbial biotechnology continues to expand, offering innovative solutions for sustainable agriculture, green energy, pollution control, and medicine. By understanding and harnessing their immense potential, we can continue to leverage these microscopic powerhouses for the greater welfare of humanity and the health of our planet.
