Abstract: Disclosed is a composition comprising a microbe expressing ferritin. The composition also comprises elemental iron in an amount of at least 3% by weight on a dry matter basis of the microbe expressing ferritin and the elemental iron. Also disclosed are ingestibles, dietary supplements, and pharmaceutical compositions comprising the composition. Also disclosed are methods for treating a subject comprising administering the composition to the subject. Also disclosed are methods of altering the composition of the gut bacterial microbiome in a subject, the method comprising administering the composition to the subject.