Why do E. coli cultures smell bad?

E. coli cultures can produce several compounds that contribute to their characteristic odor. Some of the key compounds responsible for the smell include:

Indole: Indole is a heterocyclic aromatic organic compound that has a strong, fecal-like odor. It is produced by the breakdown of tryptophan, an amino acid found in proteins. E. coli produces indole as a byproduct of its metabolism, and it is one of the main contributors to the distinctive smell of E. coli cultures.

Skatole: Skatole is another heterocyclic aromatic organic compound that has a strong, fecal odor. It is also produced by the breakdown of tryptophan. Skatole is present in higher concentrations in E. coli cultures that have been grown in the presence of high levels of tryptophan.

Hydrogen sulfide: Hydrogen sulfide is a colorless gas that has a strong, rotten egg odor. It is produced by the reduction of sulfate ions, which are present in the growth medium. E. coli produces hydrogen sulfide as a byproduct of its metabolism, and it contributes to the unpleasant smell of E. coli cultures.

Other volatile organic compounds (VOCs): In addition to indole, skatole, and hydrogen sulfide, E. coli cultures can produce various other VOCs that contribute to their smell. These VOCs include compounds such as acetic acid, butyric acid, and propionic acid, which have sour or pungent odors.

The specific odor profile of an E. coli culture can vary depending on the strain of E. coli, the growth conditions, and the presence of other microorganisms. However, the compounds mentioned above are commonly associated with the smell of E. coli cultures.