Bacteroidetes
| Bacteroidetes | |
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| Scientific classification | |
| Domain: | Bacteria |
| Phylum: |
Bacteroidetes Krieg et al. 2012 |
| Classes | |
| Synonyms | |
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The phylum Bacteroidetes is composed of three large classes of Gram-negative, nonsporeforming, anaerobic or aerobic, and rod-shaped bacteria that are widely distributed in the environment, including in soil, sediments, and sea water, as well as in the guts and on the skin of animals.
By far, the ones in the Bacteroidia class are the most well-studied, including the genus Bacteroides (an abundant organism in the feces of warm-blooded animals including humans), and Porphyromonas, a group of organisms inhabiting the human oral cavity. The class Bacteroidia was formerly called Bacteroidetes; as it was until recently the only class in the phylum, the name was changed in the fourth volume of Bergey's Manual of Systematic Bacteriology.
Some members of the genus Bacteroides are opportunistic pathogens. Rarely are members of the other two classes pathogenic to humans.
This phylum is sometimes grouped with Chlorobi, Fibrobacteres, Gemmatimonadates, Caldithrix, and marine group A to form the FCB group or superphylum. In the alternative classification system proposed by Cavalier-Smith, this taxon is instead a class in the Sphingobacteria phylum.
Comparative genomic analysis has led to the identification of 27 proteins which are present in most species of the phylum Bacteroidetes. Of these, one protein is found in all sequenced Bacteroidetes 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, four proteins have been identified which are present in all Bacteroidetes species except Cytophaga hutchinsonii; this is again likely due to selective gene loss. A further eight proteins have been identified which are present in all sequenced Bacteroidetes genomes except Salinibacter ruber. The absence of these proteins may be due to selective gene loss, or because S. ruber branches very deeply, the genes for these proteins may have evolved after the divergence of S. ruber. A conserved signature indel has also been identified; this three-amino-acid deletion in ClpB chaperone is present in all species of the Bacteroidetes phylum except S. ruber. This deletion is also found in one Chlorobi species and one Archaeum species, which is likely due to horizontal gene transfer. These 27 proteins and the three-amino-acid deletion serve as molecular markers for the Bacteroidetes.
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