People use microbes in nearly every corner of daily life, from the food on your plate to the medicine in your cabinet. Bacteria, fungi, and yeast play essential roles in producing food, manufacturing drugs, cleaning up pollution, growing crops, and treating sewage. Your own body hosts roughly 38 trillion bacterial cells, about the same number as your human cells, and many of those microbes are working in your favor too.
Bread, Beer, and Fermented Foods
One of the oldest and most familiar uses of microbes is fermentation. The yeast Saccharomyces cerevisiae has been instrumental in making bread and alcoholic beverages for thousands of years. In bread dough, yeast consumes sugar and produces carbon dioxide and ethanol. The carbon dioxide creates gas bubbles that make dough rise, while the ethanol evaporates during baking. Yeast also generates dozens of flavor and aroma compounds through its metabolism: esters that smell fruity or like pineapple, ketones that give a buttery note, and alcohols and aldehydes that add floral qualities. That complex flavor profile is why a slow-fermented loaf tastes so different from a quick one.
The same species powers beer and wine production, where the ethanol is the main product rather than a byproduct. In dairy, lactic acid bacteria convert lactose (milk sugar) into lactic acid, which thickens milk into yogurt, gives it tang, and acts as a natural preservative. Similar bacterial fermentation produces cheese, sauerkraut, kimchi, miso, and dozens of other staple foods around the world.
Antibiotics and Medicine
The discovery that microbes could kill other microbes transformed modern medicine. Alexander Fleming noticed in 1928 that a Penicillium mold produced a substance that destroyed bacteria, and he named it penicillin. He published his findings in 1929 but couldn’t purify the unstable compound himself. A decade later, Howard Florey and his team, including fungal specialist Norman Heatley, figured out how to grow the mold in large quantities and extract usable penicillin. Drug companies then scaled production using deep-tank fermentation, bubbling air through large vats to feed enormous quantities of mold. A key breakthrough came when researchers substituted corn steep liquor, a cheap waste product from cornstarch manufacturing, into the growth medium and saw penicillin yields jump dramatically.
That same approach of harvesting useful chemicals from microbial cultures led to the discovery of streptomycin, chloramphenicol, erythromycin, vancomycin, and many other antibiotics throughout the 1940s and 1950s. Today, microbes remain the starting point for a large share of the world’s antibiotic supply.
Manufacturing Human Insulin
Before the 1980s, insulin for people with diabetes came from pig and cow pancreases. That changed when scientists learned to insert the human insulin gene into bacteria using recombinant DNA technology. The bacterium E. coli became the preferred factory because it grows fast, needs simple nutrients, and produces high yields at low cost. Saccharomyces cerevisiae (the same yeast from baking) is also used for some insulin formulations.
Different engineered strains of E. coli have been optimized for this work. Some carry extra genes that help them read the human genetic code more accurately, while others have had their protein-recycling machinery disabled so they don’t break down the insulin before it can be collected. Modified versions of insulin, like long-acting formulations, are also produced this way by tweaking the protein’s structure before growing it in bacterial cultures. This same platform now produces a wide range of therapeutic proteins beyond insulin.
Cleaning Up Oil Spills
When oil contaminates ocean water, certain bacteria treat it as food. Alcanivorax borkumensis is a marine bacterium found in oceans worldwide that blooms in oil-contaminated areas and can make up 80% of the local bacterial population after a spill. Other specialized hydrocarbon-degrading genera include Oleispira, Thalassolituus, and Cycloclasticus, while species of Pseudomonas, Mycobacterium, and Rhodococcus are particularly effective at breaking down more complex petroleum compounds like the polycyclic aromatic hydrocarbons found in crude oil.
These microbes don’t always work fast enough on their own. Low levels of nitrogen and phosphorus in seawater can limit their growth, so cleanup crews sometimes “fertilize” spill zones to create better conditions for bacterial activity, a technique called biostimulation. In open ocean, soluble fertilizers wash away quickly, so oil-soluble fertilizers tend to work better. Biosurfactants are another tool: they break oil into smaller droplets, increasing the surface area bacteria can attack. When oil soaks into beach sediment, physical tilling can expose buried oil to oxygen and microbes. Temperature, wave action, oxygen levels, and the specific chemistry of the spilled oil all influence how quickly microbes can do their work.
Helping Crops Grow
Nitrogen is essential for plant growth, but most plants can’t pull it from the atmosphere on their own. Legumes like soybeans, peas, and lentils solve this problem through a partnership with soil bacteria collectively called rhizobia. When a legume plant is starved for nitrogen, it exchanges chemical signals with nearby rhizobia. The bacteria colonize the plant’s roots and trigger the formation of small, specialized structures called root nodules. Inside these nodules, the bacteria convert atmospheric nitrogen gas into a form the plant can use for building proteins and growing. In return, the plant feeds the bacteria sugars produced through photosynthesis.
This symbiosis is so effective that legume crops often need little or no synthetic nitrogen fertilizer, which is why farmers rotate legumes with other crops to naturally replenish soil nitrogen. The partnership only activates when the plant actually needs it, making it a remarkably efficient system.
Treating Wastewater
Most municipal sewage treatment depends on microbes to do the heavy lifting. In the activated sludge process, used by treatment plants worldwide, wastewater is mixed with communities of bacteria that form clumps called biological flocs. Air is pumped into the tanks to keep oxygen levels high, and the microbes consume dissolved and particulate organic matter, converting it into cell mass and carbon dioxide. The process requires a specific balance of carbon, nitrogen, and phosphorus (roughly 100:5:1 for aerobic treatment) to keep the microbial community healthy and efficient.
Anaerobic microbes handle a different stage of treatment, breaking down sludge in oxygen-free digesters and producing methane that some facilities capture as biogas for energy. Without these microbial communities, treating the billions of gallons of sewage produced daily by cities would require far more energy and chemical inputs.
Natural Pest Control
The soil bacterium Bacillus thuringiensis, commonly called Bt, is the most widely used microbial insecticide, representing about 2% of the total global insecticide market. Bt produces crystal proteins (Cry toxins) that are specifically toxic to insect larvae. When a caterpillar or beetle larva eats Bt on a leaf, the toxin binds to proteins in the insect’s midgut, forms pores in the gut wall, and causes cells to burst through osmotic shock. The gut lining breaks down, bacteria invade the body cavity, and the larva dies.
What makes Bt valuable is its specificity. Different strains produce toxins that target different insect groups, so farmers and gardeners can choose a formulation aimed at caterpillars without harming bees or beetles. Beyond sprays, the genes for Cry toxins have been engineered directly into crop plants like corn and cotton, creating varieties that produce their own insect protection throughout the growing season.
Industrial Chemical Production
Many everyday chemicals are produced by microbial fermentation rather than traditional chemistry. The most striking example is citric acid, the tart compound found in soft drinks, candies, cleaning products, and pharmaceuticals. About 90% of the world’s citric acid is produced by the fungus Aspergillus niger, grown in large fermentation tanks. This is far more economical than extracting citric acid from citrus fruits, which is how it was originally sourced. Microbes are similarly used to produce enzymes for laundry detergents, amino acids for food and animal feed, and organic acids for industrial processes, making fermentation one of the backbone technologies of modern manufacturing.