Bacteria (Kingdom); Bacteroidetes (Phylum); Bacteroidetes (Class); Bacteroidales(Order); Porphyromonadaceae (Family); Porphyromonas (Genus)
Description and Significance
Porphyromonas endodontalis is a black pigmented gram-negative microbe associated with periodontitis, endodontic infections, gingivitis and tooth pulp necrosis.  P. endodontalis have shown optimum growth in culture around 37 degrees Celsius and slightly alkaline environments. It differs from other members of the genus in that a major product of the bacteria is succinate. Related microbes of the genus such as P. gingivalis and P. asaccharolytica are also black pigmented bacteria and native to the oral cavity.
Structure, Metabolism, and Life Cycle
Porphyromonas endodontalis are anaerobic, black pigmented, nonsporeforming, nonmotile rods that utilize nitrogeneous substrates as energy sources.  The black pigment is observed in colonies after 7 to 14 days. The major pigment associated to the dark color is protoheme, although protoporphyrin is also associated to the color. Much like other gram-negative bacteria, Prophyromonas endodontalis has a cell wall made of peptidoglycan that has a high concentration of lysine.  The major products of fermentation are n-butyric and acetic acids as well as lower levels of propionic , isobutyric, and isovaleric acids.
Ecology and Pathogenesis
Porphyromonas endodontalis forms black colonies on gingival epitheal cells. The colonization of this microbe causes periapical lesions with acute symptoms such as pain, swelling, and suppuration.  Studies have shown that P. endodontalis is mainly found in symptomatic oral infections but can also be found in asymptomatic infections. It is suggested that P. endodontalis causes infections by releasing outer membrane blebs which may contain a lipopolysaccharide.  Other possible virulence factors include capsule, proteases and toxic metabolic products.  The mechanism of how P. endodontalis adheres to gingival epithelial cells is different from related bacteria and a current subject of research.
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Page authored by Isaac Colden, student of Mandy Brosnahan, Instructor at the University of Minnesota-Twin Cities, MICB 3301/3303: Biology of Microorganisms.