Bacillus subtilis natto produces poly-glutamic acid as it consumes amino acids
Natto is a fermented soybean product created by Bacillus subtilis natto, a rod-shaped bacterium that colonizes steamed soybeans and produces the characteristic ropy, sticky texture. The stickiness comes from poly-glutamic acid (polyglutamate), a polymer that the bacteria synthesize and secrete as a capsule around the cells. This biopolymer is produced when the bacteria metabolize glutamate and other amino acids from soy protein breakdown.
The bacterial growth is rapid (24-48 hours at 37-42C) and produces ammonia and other compounds that give natto its distinctive pungent smell. The sticky matrix holding the beans together is pure polyglutamate, which accounts for the gooey texture and the characteristic long strings when you pull apart a spoonful.
Fermentation and flavor integration
Traditional natto fermentation relies on inoculation with starter culture, then incubation in a warm, humid environment. The bacteria prefer oxygen but can tolerate anaerobic conditions, so fermentation can happen in sealed containers. The ammonia produced during fermentation mellows over time, developing into a umami-rich aroma. Cold storage stops bacterial growth but the polyglutamate strands and bacterial metabolites remain stable, so natto flavor actually improves over a few days of refrigeration.