Actinobacteria: A relevant minority for the maintenance of gut homeostasis.

Actinobacteria are one the four major phyla of the gut microbiota and, although they represent only a small percentage, are pivotal in the maintenance of gut homeostasis. During the last decade many studies focused the attention on Actinobacteria, especially on their role both in gastrointestinal and systemic diseases and on their possible therapeutic use. In fact, classes of this phylum, especially Bifidobacteria, are widely used as probiotic demonstrating beneficial effects in many pathological conditions, even if larger in vivo studies are needed to confirm such encouraging results. This review aims to explore the current knowledge on their physiological functions and to speculate on their possible therapeutic role(s) in gastrointestinal and systemic diseases.