Not All of Them Are the Enemy

Microbes are genuinely everywhere, in soil, water, air, inside bodies, even in places no other life form could survive at all, thermal vents as hot as 100 degrees Celsius, deep soil layers, under metres of snow, in highly acidic environments, spanning protozoa, bacteria, fungi, microscopic plant and animal viruses, viroids and even prions, proteinaceous infectious agents with no genetic material at all; many bacteria and fungi can be grown on nutritive media to form visible colonies, genuinely useful for studying them directly. The previous chapter in this thread covered how microbes cause disease, but that is only ever part of the picture, and this chapter covers the other part: several genuinely useful contributions microbes make to daily human life. Curd's production is a genuinely everyday example: lactic acid bacteria, Lactobacillus among them, grow in milk and produce acids that coagulate and partially digest its proteins, converting milk into curd while actually boosting its vitamin B12 content, and a small amount of existing curd added to fresh milk as a starter culture, containing millions of these bacteria, is enough to convert an entire fresh batch at the right temperature; the same lactic acid bacteria play a genuinely useful role checking disease-causing microbes once inside the human stomach too. The characteristically puffed-up dough used for dosa and idli owes its texture to bacterial fermentation producing carbon dioxide gas directly, while bread dough is fermented instead by baker's yeast, Saccharomyces cerevisiae. Traditional drinks and foods extend this same principle widely: toddy, a traditional drink in parts of southern India, comes from fermented palm sap, and fermentation is similarly used to prepare fish, soybean and bamboo shoots as food. Cheese is one of the oldest microbially-produced foods of all, its specific texture, flavour and taste directly determined by the particular microbe used, the large characteristic holes in Swiss cheese, for instance, coming from carbon dioxide produced by the bacterium Propionibacterium sharmanii, while Roquefort cheese gets its distinctive flavour from a specific fungus deliberately grown on it during ripening.

Yeasts, Saccharomyces cerevisiae specifically, the same species used for bread-making and here called brewer's yeast, have been used since ancient times to ferment malted cereals and fruit juices into ethanol, producing wine, beer, whisky, brandy and rum, with the exact drink produced depending on the raw material fermented and whether the resulting broth is distilled afterward; wine and beer are produced without distillation, while whisky, brandy and rum all require distilling the fermented broth further. Producing any of these at genuine industrial scale requires growing the yeast in very large vessels called fermentors, allowing the same basic fermentation process to run at a scale far beyond anything possible in a home kitchen.

Antibiotics, chemical substances produced by some microbes capable of killing or slowing the growth of other, disease-causing microbes, rank among the twentieth century's most consequential discoveries, and their very name captures a genuine irony: 'anti' plus 'bio', literally 'against life', describes their effect on disease-causing organisms specifically, even as they are entirely 'pro-life' from the human patient's own perspective. Penicillin, the first antibiotic ever discovered, came about through genuine accident: Alexander Fleming, working with Staphylococcus bacteria, noticed a mould growing in one of his unwashed culture plates, and that the Staphylococcus simply could not grow anywhere near it; tracing this effect to a specific chemical produced by the mould, he named it Penicillin after the mould itself, Penicillium notatum, though its full therapeutic potential was only properly established later, by Ernest Chain and Howard Florey, whose work let Penicillin be used extensively to treat wounded American soldiers during World War II; Fleming, Chain and Florey shared the 1945 Nobel Prize for this discovery. Further antibiotics, purified from other microbes in the years since, together transformed medicine's ability to treat once-deadly diseases like plague, whooping cough, diphtheria and leprosy, diseases that had killed millions worldwide before antibiotics existed, making a world without antibiotics genuinely difficult to imagine today.

Microbes also drive commercial production of a genuinely wide range of chemicals beyond antibiotics alone. Organic acids come from specific microbial sources: citric acid from the fungus Aspergillus niger, acetic acid from the bacterium Acetobacter aceti, butyric acid from Clostridium butylicum, and lactic acid from Lactobacillus, while Saccharomyces cerevisiae additionally handles commercial ethanol production. Microbially produced enzymes serve genuinely practical roles too: lipases, added to detergent formulations, help remove oily stains from laundry, while pectinases and proteases clarify bottled fruit juice, exactly why store-bought juice looks noticeably clearer than juice made fresh at home. Streptokinase, produced by Streptococcus bacteria and refined through genetic engineering, works as a genuine 'clot buster', clearing blood clots from the vessels of heart attack patients. Cyclosporin A, produced by the fungus Trichoderma polysporum, works as an immunosuppressive agent essential for organ-transplant patients, directly connecting back to this thread's earlier coverage of cell-mediated immunity's role in graft rejection. Statins, produced by the yeast Monascus purpureus, have been commercialised as cholesterol-lowering drugs, working by competitively inhibiting the specific enzyme responsible for the body's own cholesterol synthesis.

Cities and towns generate genuinely enormous quantities of waste water daily, largely human excreta, called sewage, carrying large amounts of organic matter and microbes, many of them pathogenic, making direct discharge into rivers or streams genuinely unsafe; sewage is instead treated at sewage treatment plants, using the same heterotrophic microbes already naturally present in the sewage itself, run in two distinct stages. Primary treatment handles physical removal only: floating debris removed by sequential filtration, then grit, soil and small pebbles, removed by sedimentation, with everything that settles forming primary sludge and the remaining liquid, the effluent, moving forward to secondary treatment. Secondary, or biological, treatment passes this effluent into large aeration tanks, mechanically agitated and pumped full of air, letting aerobic microbes grow vigorously into flocs, mesh-like masses of bacteria intertwined with fungal filaments, which consume the bulk of the effluent's remaining organic matter as they grow, significantly reducing its biochemical oxygen demand, or BOD, a direct measure of how much oxygen bacteria would need to fully oxidise all the organic matter in a litre of the water, and therefore a direct measure of the water's actual polluting potential; treatment continues specifically until this BOD is reduced enough. The treated effluent then moves to a settling tank, where the bacterial flocs settle out as activated sludge, a small portion recycled back into the aeration tank as fresh inoculum and the bulk pumped instead into large anaerobic sludge digesters, where a different set of anaerobic bacteria further digest the sludge's bacteria and fungi, producing a mixture of methane, hydrogen sulphide and carbon dioxide, together forming a genuinely usable, flammable biogas. The final secondary effluent is then released into natural water bodies. This microbial sewage-treatment method, in continuous use for over a century worldwide, remains genuinely unrivalled by any purely artificial technology, though India's rapid urbanisation has outpaced treatment plant capacity, pushing untreated sewage directly into rivers and worsening water-borne disease, a problem the Ganga Action Plan and Yamuna Action Plan specifically aim to address through expanded treatment infrastructure.

Biogas, a fuel-usable gas mixture dominated by methane, forms directly through microbial metabolism, the exact gas produced depending on which microbe and which organic substrate is involved; where dough fermentation, cheese-making and beverage production mainly produce carbon dioxide, certain bacteria growing anaerobically on cellulosic material instead produce substantial methane alongside carbon dioxide and hydrogen, collectively called methanogens, Methanobacterium being one common example, naturally found both in anaerobic sewage sludge and inside cattle rumen, the specific stomach chamber where cellulose from cattle feed actually gets broken down, a digestive capacity humans genuinely lack entirely. Cattle dung, or gobar, correspondingly carries a rich population of exactly these bacteria, making it a genuinely effective biogas, or gobar gas, source. A typical biogas plant consists of a deep concrete tank holding a dung slurry, topped with a floating cover that rises as gas accumulates inside, connected to an outlet pipe supplying nearby houses directly, while the spent slurry, removed through a separate outlet, doubles usefully as fertiliser. Because cattle dung is available in genuinely large quantities specifically in rural areas, biogas plants are correspondingly built there most often, supplying fuel for cooking and lighting; India's own biogas technology owes much of its development specifically to the Indian Agricultural Research Institute and the Khadi and Village Industries Commission.

Modern agriculture has increasingly relied on chemical insecticides, pesticides and weedicides to control pests and disease, but these chemicals are genuinely toxic, harmful to humans and animals alike, and pollute soil, groundwater, fruit, vegetables and crops directly, a problem organic farming's philosophy addresses differently entirely: rather than eradicating so-called pests outright, an approach that indiscriminately kills useful and harmful organisms together, organic farming works to keep pest populations at manageable levels through a genuinely complex web of natural checks and balances within a living ecosystem, recognising that beneficial predatory and parasitic insects actually depend on some pest populations surviving as their own food source or host. Ladybirds and dragonflies, familiar non-microbial predators, control aphids and mosquitoes respectively this way, while microbial biocontrol adds a further, genuinely targeted layer: Bacillus thuringiensis, commonly called Bt, sold as dried spores mixed with water and sprayed onto vulnerable crops like brassicas and fruit trees, releases a toxin once eaten by insect larvae specifically, killing the caterpillars while leaving every other insect entirely unharmed; genetic engineering has since let scientists introduce Bt's own toxin genes directly into crop plants, Bt cotton, grown in several Indian states, being a direct product of this approach. Trichoderma, a free-living fungus common throughout root ecosystems, works as an effective biocontrol agent against several plant pathogens directly. Baculoviruses, insect and arthropod pathogens, mostly from the genus Nucleopolyhedrovirus, offer a genuinely narrow-spectrum, species-specific insecticidal option, demonstrated to have no negative effects on plants, mammals, birds, fish or non-target insects at all, making them especially valuable within integrated pest management programmes or in genuinely ecologically sensitive areas.

Chemical fertiliser overuse contributes significantly to environmental pollution, driving real, growing interest in biofertilisers instead, organisms that directly enrich soil nutrient quality, sourced mainly from bacteria, fungi and cyanobacteria. Rhizobium, forming the familiar symbiotic root nodules on leguminous plants, fixes atmospheric nitrogen into organic forms the plant can actually use directly, while other bacteria, Azospirillum and Azotobacter among them, fix atmospheric nitrogen while living freely in the soil instead, enriching its nitrogen content without needing any specific plant partnership at all. Fungi form their own symbiotic partnership with plants too, called mycorrhiza; Glomus, a genuinely common example, absorbs phosphorus from soil and passes it directly to its plant partner, and plants carrying such fungal partnerships show further real benefits too, greater resistance to root pathogens, better tolerance to salinity and drought, and generally improved growth and development overall. Cyanobacteria, autotrophic microbes spread widely across both aquatic and terrestrial environments, Anabaena, Nostoc and Oscillatoria among them, can fix atmospheric nitrogen too, serving as a genuinely important biofertiliser specifically in paddy fields, while also directly adding organic matter to soil and improving its fertility more broadly; a range of biofertiliser products are now commercially available in India, letting farmers actively replenish soil nutrients while reducing their dependence on chemical fertiliser.