Microbes: Bacteria, Fungi, and Household Uses

• Microbes are major components of Earth's biological systems, as diverse as protozoa, bacteria, fungi, microscopic animal and plant viruses, viroids, and prions
• These organisms are ubiquitous, thriving in soil, water, air, and within bodies, as well as in extreme conditions like geysers up to 100°C and deep under snow.
• Bacteria and fungi can be cultured to form visible colonies, useful for microorganism research.

Microbes in Household Products

• Microbes or their derivatives are part of everyday life, like using Lactobacillus and other lactic acid bacteria (LAB) to turn milk into curd.
• During curdling, LAB multiply in milk, producing acids that coagulate and partially digest milk proteins improving nutritional quality by increasing vitamin B12 content.
• LAB also checks disease-causing microbes in the stomach.
• Bacteria also ferment dough for foods like dosa and idli, with the puffed-up appearance due to CO2 production.
• Baker's yeast (Saccharomyces cerevisiae) can be used similarly to ferment dough for bread.
• Traditional drinks and foods are produced via microbial fermentation, like 'Toddy' from palm sap in southern India.
• Microbes are used to ferment more foods like fish, soyabeans and bamboo shoots.
• Different microbes give cheese varieties textures, flavours and tastes, for example:
  • The large holes in 'Swiss cheese' are from the bacterium Propionibacterium sharmanni.
  • 'Roquefort cheese' is ripened by growing specific fungi on it.

Microbes in Industrial Products

• Microbes synthesize valuable products like beverages and antibiotics.
• Industrial production involves cultivating microbes in large vessels called fermenters.

Fermented Beverages

• Yeasts, especially Saccharomyces cerevisiae (also known as brewer’s yeast), have long been used to produce beverages like beer, wine, whisky, brandy and rum by fermenting malted cereals and fruit juices into ethanol.
• Alcoholic drinks vary, from wine and beer produced without distillation, to whisky, brandy and rum produced via distillation of the fermented materials.

Antibiotics

• Antibiotics, which are antimicrobial substances produced by microbes, are a major 20th century discovery
• They have contributed to human welfare significantly.
• The word "antibiotic" means "against life."
• The first antibiotic, Penicillin, was discovered by Alexander Fleming and later fully established by Chain and Florey.
• Fleming found Penicillium notatum growing in a culture plate and inhibiting Staphylococci growth.
• Penicillin was used to treat American soldiers in World War II, and Fleming, Chain, and Florey were awarded the Nobel Prize in 1945.
• Antibiotics can treat deadly diseases like plague, whooping cough, diphtheria, and leprosy.

Chemicals, Enzymes and other Bioactive Molecules

• Microbes produce organic acids, alcohols, and enzymes on a commercial scale.
  • Aspergillus niger produces citric acid.
  • Acetobacter aceti produces acetic acid.
  • Clostridium butylicum produces butyric acid.
  • Lactobacillus produces lactic acid.
• Yeast (Saccharomyces cerevisiae) is also used commercially for ethanol production.
• Lipases are used in detergents to clear oily stains.
• Pectinases and proteases clarify bottled fruit juices.
• Streptokinase, made by Streptococcus bacteria and modified through genetic engineering, is used as a clot buster for patients with myocardial infarction.
• Cyclosporin A, an immunosuppressant for organ transplant patients, comes from the fungus Trichoderma polysporum.
• Statins, from the yeast Monascus purpureus, are used to lower blood cholesterol levels.

Microbes in Sewage Treatment

• Sewage, consisting of human waste and wastewater, is treated in sewage treatment plants (STPs) to reduce pollution before disposal.
• The treatment uses heterotrophic microbes and occurs in two stages.

Primary Treatment

• Primary treatment involves physical removal of large and small particles via filtration and sedimentation.
• Floating debris is removed by filtration, and grit (soil and pebbles) by sedimentation.
• Solids that settle form the primary sludge, and the remaining liquid forms the effluent.

Secondary or Biological Treatment

• Secondary treatment involves passing primary effluent into aeration tanks, where it's mechanically agitated and aerated to promote aerobic microbial growth into flocs
• Microbes in flocs consume organic matter, which reduces the biochemical oxygen demand (BOD).
• BOD indicates how much oxygen microbes would consume to oxidize organic matter in a liter of water, and indirectly measures amount of organic matter in the water.
• Post BOD reduction, the effluent is passed into settling tanks where bacterial 'flocs' sediment, forming activated sludge.
• A part of the activated sludge is used as inoculum in the aeration tank.
• The remaining sludge is transferred to anaerobic sludge digesters, where anaerobic bacteria digest the bacteria and fungi, producing biogas (methane, hydrogen sulphide, and carbon dioxide) used as an energy source.

Microbes in Production of Biogas

• Biogas, mainly methane, is produced by microbial activity and can be used as fuel.
• The type of gas produced depends on the microbes and substrates used.
• Methane-producing bacteria, or methanogens, grow anaerobically on cellulosic material
  • Methanobacterium is one.
• Methanogens are found in anaerobic sludge and in the rumen of cattle, aiding in cellulose breakdown.
• The excreta of cattle contains bacteria and can be used for biogas (gobar gas) production.
• A biogas plant contains a 10-15 feet deep concrete tank, slurry of dung and bio-wastes, and a floating cover.
• As gas is produced, the cover rises in the tank and then flows out and the slurry is removed and used as fertilizer.
• The technology was developed in India by IARI and KVIC

Microbes as Biocontrol Agents

• Biocontrol uses biological methods to control plant diseases and pests, reducing dependence on chemicals like insecticides and pesticides.
• Organic farmers promote biodiversity to create balance, managing pests via checks and balances without eradicating them completely.
• An important part of biological farming focuses on learning about life forms, predators, pests, life cycles, feeding patterns, and habitats to create effective biocontrol methods.
• Common examples of biocontrol agents:
  • The ladybird beetle and dragonflies control aphids and mosquitoes.
  • Bacillus thuringiensis (Bt) controls butterfly caterpillars. Bt are available as dried spores to spray vulnerable plants, killing insect larvae through toxin release.
  • Genetic engineering has introduced Bt toxin genes into plants for insect resistance, Bt-cotton is being cultivated in some states of the country.
  • Trichoderma fungi are used in treating plant diseases due to their root ecosystems.
  • Baculoviruses, used as biological control agents, attack insects, without negative impacts on plants, mammals, birds or fish.

Microbes as Biofertilisers

• Biofertilisers enrich soil via organisms like bacteria, fungi, and cyanobacteria as an alternative to chemical fertilisers.
• Symbiotic Rhizobium in leguminous plant root nodules fix atmospheric nitrogen.
• Free-living bacteria in soil like Azospirillum and Azotobacter also fix atmospheric nitrogen.
• Fungi form mycorrhizal associations with plants, like Glomus, which absorbs phosphorus from soil and improves resistance to pathogens and stress. Plants grow overall better.
• Cyanobacteria are autotrophic microbes in terrestrial environments that fix atmospheric nitrogen, such as Anabaena, Nostoc, and Oscillatoria.
• Cyanobacteria are important biofertilisers especially in paddy fields, that also add organic matter to the soil.