One of several saprophytic, filamentous, anaerobic bacteria of the genus Actinomyces, certain species of which are pathogenic for humans and animals: Actinomyces are known for causing diseases in humans and for the important role they play in soil ecology.

Actinomyces produce a number of enzymes that help degrade organic plant material, lignin and chitin. As such, their presence is important in the formation of compost.