Food and drink
Fermentation is the process by which yeast/bacteria convert sugars and carbohydrates to alcohol and CO2. Without these germs we’d never have bread, beer, wine, cheese or vinegar.
The most famous fungus in history is penicillium notatum, the first antibiotic. Penicillin isolated from the fungus prevents bacteria from forming new cell walls.
A start-up in California has engineered bacteria to ferment renewable feedstock (grains, grasses, etc) into diesel fuel. Ethanol is chemically similar to alcohol.
Water hyacinths have the uncanny ability to soak up raw sewage. Bacteria live on their roots, breaking down organic matter into nutrients the plants can use.
In 500 BCE, archers would dip arrowheads in a putrid mix of dung, snake venom, human blood and decomposing flesh to poison the enemy with a potent microbial mix.