Bacterial adaptation is associated with tryptophan metabolism and persistence of nontypeable Haemophilus influenzae.

Loss of tryptophan biosynthesis reduces intracellular bacterial community persistence of nontypeable Haemophilus influenzae, while both biosynthesis and import mutants show increased fitness in experimental otitis media.

• Why it matters: Nutrient stress–driven microevolution may help Haemophilus influenzae invade, form intracellular communities, and persist during infection, but the specific metabolic dependencies are unclear.
• What they did: The evolved strain carried a reprioritizing mutation in cyclic AMP phosphodiesterase, increasing proteins in tryptophan biosynthesis; mutational analyses then tested viability and IBC persistence with disrupted tryptophan biosynthesis versus import, followed by an experimental otitis media model.
• The result: In vitro, viability depends on tryptophan biosynthesis but not import, and IBC persistence decreases without biosynthesis; in otitis media, both biosynthesis and import mutants increase fitness versus the parental strain, and the trp operon includes a ydfG ortholog linked to oxidative stress resistance that is more frequent in mucosal-associated strains.

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