Bacteroidota

Bacteroides fragilis was the first Bacteroides species isolated in 1898 as a human pathogen linked to appendicitis among other clinical cases. For a long time, it was thought that the majority of Gram-negative gastrointestinal tract bacteria belonged to the genus Bacteroides, but in recent years many species of Bacteroides have undergone reclassification. Based on current classification, the majority of the gastrointestinal Bacteroidota species belong to the families Bacteroidaceae, Prevotellaceae, Rikenellaceae, and Porphyromonadaceae. In the alternative classification system proposed by Cavalier-Smith, this taxon is instead a class in the phylum Sphingobacteria. == Medical and ecological role ==

In the gastrointestinal microbiota Bacteroidota have a very broad metabolic potential and are regarded as one of the most stable part of gastrointestinal microflora. Reduced abundance of the Bacteroidota in some cases is associated with obesity. This bacterial group as a whole has conflicting evidence for alteration of abundance in patients with irritable bowel syndrome, though its genus Bacteroides is likely enriched, but it may be involved in type 1 and type 2 diabetes pathogenesis. For example, Bacteroidota, together with "Pseudomonadota", "Bacillota", and "Actinomycetota", are also among the most abundant bacterial groups in rhizosphere. They have been detected in soil samples from various locations, including cultivated fields, greenhouse soils and unexploited areas. == Metabolism ==

Gastrointestinal Bacteroidota species produce succinic acid, acetic acid, and in some cases propionic acid, as the major end-products. Species belonging to the genera Alistipes, Bacteroides, Parabacteroides, Prevotella, Paraprevotella, Alloprevotella, Barnesiella, and Tannerella are saccharolytic, while species belonging to Odoribacter and Porphyromonas are predominantly asaccharolytic. Some Bacteroides spp. and Prevotella spp. can degrade complex plant polysaccharides such as starch, cellulose, xylans, and pectins. The Bacteroidota species also play an important role in protein metabolism by proteolytic activity assigned to the proteases linked to the cell. Some "Bacteroides spp. have a potential to utilize urea as a nitrogen source. Other important functions of Bacteroides spp. include the deconjugation of bile acids and growth on mucus. ==Genomics==

Comparative genomic analysis has led to the identification of 27 proteins which are present in most species of the phylum Bacteroidota. Of these, one protein is found in all sequenced Bacteroidota species, while two other proteins are found in all sequenced species with the exception of those from the genus Bacteroides. The absence of these two proteins in this genus is likely due to selective gene loss. Additionally, the phylum Fibrobacterota is indicated to be specifically related to these two phyla. A clade consisting of these three phyla is strongly supported by phylogenetic analyses based upon a number of different proteins Lastly and most importantly, two conserved signature indels (in the RpoC protein and in serine hydroxymethyltransferase) and one signature protein PG00081 have been identified that are uniquely shared by all of the species from these three phyla. All of these results provide compelling evidence that the species from these three phyla shared a common ancestor exclusive of all other bacteria, and it has been proposed that they should all recognized as part of a single "FCB" superphylum. ==Phylogeny==

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature ==See also==