Dysbiotic Proteobacteria expansion: a microbial signature of epithelial dysfunction. 
A balanced gut microbiota is important for health, but the mechanisms maintaining homeostasis are incompletely understood.  Anaerobiosis of the healthy colon drives the composition of the gut microbiota towards a dominance of obligate anaerobes, while dysbiosis is often associated with a sustained increase in the abundance of facultative anaerobic Proteobacteria, indicative of a disruption in anaerobiosis.  The colonic epithelium is hypoxic, but intestinal inflammation or antibiotic treatment increases epithelial oxygenation in the colon, thereby disrupting anaerobiosis to drive a dysbiotic expansion of facultative anaerobic Proteobacteria through aerobic respiration.  These observations suggest a dysbiotic expansion of Proteobacteria is a potential diagnostic microbial signature of epithelial dysfunction, a hypothesis that could spawn novel preventative or therapeutic strategies for a broad spectrum of human diseases.