Proteobacteria

Proteobacteria (gram-negative bacteria) are a major phylum of bacteria, which includes a wide variety of pathogenic bacteria, including Escherichia, Salmonella, Vibrio, Helicobacter, and Yersinia. Other bacteria within Proteobacteria are nonpathogenic while some are even responsible for nitrogen fixation, the process of converting nitrogen from the atmosphere into ammonia. Nitrogen fixation is essential for all forms of life.

The phylum was discovered in 1987 by Carl Woese, an American microbiologist, who described the group as ‘purple bacteria and their relatives.’ Because of the great diversity of morphologies found in this group, Proteobacteria are named after Proteus, a sea-god capable of taking on various forms.

Many Proteobacteria move via flagella, but some species are nonmotile or rely on bacterial gliding. In addition, the metabolic processes of Proteobacteria are extremely diverse. Most members are facultatively or obligately anaerobic, heterotrophic or chemoautotrophic; however, there are several exceptions. A variety of genera not closely related to each other utilize photosynthesis to convert energy from light.

Typically, all Proteobacteria account for approximately 1% of the gut microbiome. Members of five different classes of Proteobacteria, specifically the Alpha-, Beta-, Gamma-, Delta- and Epsilonproteobacteria are often found in the gastrointestinal microbiota, and among these groups Enterobacteriaceae within the Gammaproteobacteria class are the most abundant.

Proteobacteria in Dysbiosis

Proteobacteria, when found in high abundance, have been linked with inflammation and imbalance of the lower reproductive tract of women and the gastrointestinal (GI) tract.

Recent advances in sequencing have provided convincing evidence that the GI tract is home to a complex microbial community. The communities found in the gut are thought to be critical determinant of health related to metabolism and inflammation. Although the human gut flora includes relatively small numbers of this phylum naturally, increased abundance of the phylum Proteobacteria may indicate an imbalanced gut microbiome. Studies have extensively explored the correlation between increases of Proteobacteria and a compromised gut microbiome. Some researchers have proposed that increased populations of Proteobacteria may be used as a screening tool for dysbiosis and risks of disease in the future.

References

Holdeman LV, Good IJ & Moore WEC (1976) Human fecal flora: variation in bacterial composition within individuals and a possible effect of emotional stress. Appl Environ Microbiol 31: 359–375.Shin, N.R., Whon, T.W., Bae, J.W. PMID: 938032

Shin, N.R., Whon, T.W., Bae, J.W. Proteobacteria: microbial signature of dysbiosis in gut microbiota. Trends Biotechnology. 2015. 33(9):496-503. doi: 10.1016/j.tibtech.2015.06.011

Stackebrandt, E., Murray, R.G.E., Truper, H. G. Proteobacteria classis nov., a Name for the Phylogenetic Taxon That Includes the "Purple Bacteria and Their Relatives.” International Journal of Systematic Bacteriology. 1988. 38 (3): 321–325. doi:10.1099/00207713-38-3-321