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By using stable isotope tracers and analyzing gene expression, the researchers showed that S. gordonii releases a substance called ornithine that prompts F. nucleatum to produce more of a molecule called polyamine.

Because F. nucleatum needs methionine to produce polyamine, this enhanced polyamine production activates its methionine salvage pathway, which in turn results in increased CH3SH production.

Spermidine is a type of molecule called a polyamine.

This finding led the authors to speculate that polyamine export might be involved in protecting cells against oxidative stress.

Although yeast cells have not previously been reported to produce cadaverine, they make another polyamine, putrescine, by decarboxylating the amino acid ornithine4.