Proteobacteria, contains most of the commonly known species, such as Escherichia coli and Pseudomonas aeruginosa.

Higher abundance of Proteobacteria is considered a sign of microbial imbalance(dysbiosis, which can occur during gut inflammation or metabolic disorders). Proteobacteria help their host metabolize protein, carbohydrates, and vitamins.

• Shin, N.-R., Whon, T. W. & Bae, J.-W. Proteobacteria: microbial signature of dysbiosis in gut microbiota. Trends Biotechnol. 33, 496–503 (2015).