A Microbial Biorealm page on the genus Prevotella Melaninogenica
Higher order taxa
Cellular organisms; Bacteria; Bacteroidetes/Chlorobi group; Bacteroidetes; Bacteroidetes (class); Bacteroidales; Prevotellaceae; Prevotella
Prevotella melaninogenica Synonym: Bacteroides melaninogenicus subsp. melaninogenicus
Description and significance
Prevotella melaninogenica is generally found in the oral cavity causing opportunistic pathogen in humans and at the rumen of cattle and sheep which helps to break down protein and carbohydrates food. Similar to all species of the genus Prevotella, it is strictly anaerobic, gram-negative bacterium with non-spore forming coccobacilli. When Prevotella melaninogenica grows on blood-containing media, it gives black pigment that can be easily seen in adults with rapidly progressing periodontitis lesions. This bacterium is nonmotile, therefore usually forms biofilm. In addition, P. melaninogenica includes those organisms which hydrolyze esculin but not starch and produce acid in peptone-yeast-glucose medium and peptone-yeast-mannose medium. It is catalase negative, indole negative, lipase negative and bile sensitive. It also liquefies gelatin and clots milk which shows this organism is very acidic. Because of its acidity it prevents the bovine disease of rumen acidosis; however, it affects milk production due to too much acid in stomach. The genus Prevotella used to be part of the genus Bacteroides, therefore, there are similarities that these two genera share.
The genome of Prevotella melaninogenica was sequenced using the hemolytic strain P. melaninogenica 361B. After this strain is transformed into E. coli MC1061 and screened for hemolytic clones, four clones were identified. One of these strains, HA1001, was used for sequence analysis. It is 3,033 bp long and computer analysis found two open reading frames in the insert: glnA and phyA. However, glnA holds strong homology to the amino terminal half of the Beacteroides fragilis gene. This has circular topology with a 43% G+C content. B. Fragilis is composed of 4184 protein coding genes with 92 structural RNAs. This genome also contains 71 pseudo genes that resembles a gene however lacks a genetic function. This similarity in genome of the genus Bacteroides and the genus Prevotella also shows that they have many resemblances they share. Currently P. intermedia and P. ruminicola are being sequenced.
Cell structure and metabolism
Prevotella melaninogenica is a gram-negative bacterium. Between outer and inner cell wall the membrane proteins are present in order to break down and hydrolyze the nutrients. Gram-negative bacterium has large periplasm where degradation of enzymes, attachment to proteins and impression of environment take place. The current studies have found that the enzyme that proceeds preteinase activity are located at the surface and within the P. melaninogenica.
Prevotella malaninogenica hydrolyzes esculin but not starch. Esculin is blue florescent glucoside which gets hydrolyzed to glucose and esculetin (6,7-dihydroxycoumarin) due to heat and acid. This method can proceed also through amylolytic fermentation using ATP. This ATP is created through the process of substrate level phspholyration which generates ATP during catabolism and sets the membrane gradient. This organism does not reduce urease or nitrogen which could mean that P. melaninogenica only receives its nutrients from organic donor. This organism produces acetic, isobutyric and isovaleric acids. From this metabolism process, hydrolysis of esculin can be determined by measuring acid production from the fermentation of glucose and detection of esculetin by its reaction with iron which forms black colored pigments.
Prevotella melaninogenica can be commonly found and isolated from severe anaerobic infections of the intestinal tract, the female genital tract, the upper and lower respiratory tract and the sites of osteomyelitis. At the oral cavity, B. melaninogeniucs subspecies along with P. melaninogenica and B. gingivalis are found in supragingival plaque, subgingival plaque, saliva and buccal mucosa, tonsil area and occlusal surface. Past studies show that there is increase in prevalence during the period of mixed dentition. P. melaninogenica is inhibited by the presence of iron, therefore, this organism tends to stay at the iron limiting condition such as cervicular fluid.
Prevotella melaninogenica play a major role in transmissible subcutaneous infections produced by complex mixtures of indigenous oral bacteria. It tends to produce hydrogen sulfide, ammonia and cytotoxic substances. P. melaninogenica also inhibit phagocytosis and killing of other bacteria. It stimulates the host immune system to produce substances with tissue-destorying potential. Along with P. melaninogenica, B melnaninogenicus subsp. Intermedius and B. gingivalis appear to be importanct periodontopathic organisms. Prevotella melaninogenica is also associated with its ability to become hemolysin. Therefore, it is able to lyse erythocytes such as red blood cell. It is proven to serve as virulence factors in many medically relevant pathogenic microorganisms. Along with its ability to lyse red blood cells, it can lyse other cells as well such as mast cells, neutrophils and polymorphonuclear cells. This bacterium directly damage host tissues and induce an inflammatory response. However, production of hemolysin by P. melaninogenica occurred only under iron-limiting conditions; magnesium and calcium were found to inhibit the reaction. This activity can be also found in subcellular fractions such as cytoplasmic, outer membrane and vesicle fractions. P. melaninogenica is also known to affect neuraminidase, collagenase, specific immunoglobulin G and IgA proteases.
Most of current studies that are performed engage highly with the ability of P. melaninogenica becoming a pathogen.
In 2004, research on “Bacteremia Following Surgical Dental Extraction with an Emphasis on Anaerobic Strains” took place. Researchers found out that bacteremia, which has its ability to reproduce the bacteria in the blood stream, take at least 30 minutes after the extraction. This suggests the previously held notion was wrong, that is that it takes only 10 minutes for the bacteremia to spread. In addition, researchers also found that majority of bacterial species found in blood samples after dental treatment are anaerobic, including P. melaninogenica. Since most of the species which cause disease are anaerobic, this research proposed the further study on the importance of anaerobic bacteria of oral origin.
In 2005, study on proteinase activity of Prevotella species in oral infection proceeded. The focus was to find out more information on the preteolytic activity of Prevotella species other than P. intermedia and P. nigrescens. The samples were gathered from orofacial purulent infections which includes dentoalveolar infection. They proved that the activities of preoteinase is similar to P.intermedia and P.negrescens; however, other species perform less activity when compared to two well known species. This study also shows that these enzymes that do proteolytic activity are mainly located within the cell or on the cell surface. In addition, this experiment shows that clinical strains of P. melaninogenica had significantly higher protelytic activity than strains from healthy mouth. Along with these information, it is now proved that n-ethylmaleimide and phenylmethansulfonyl fluoride inhibit the proteolytic activity of all Prevotella species, and iodoacetate decreased activity of all Prevotella species.
In 2006, study on the quality of vitamin C as the antioxidant and pro-oxidant performed using anaerobic organism including P. melaninogenica. This research found out that with exposure to oxygen, the presence of vitamin C enhances oxidative DNA damage even while suppressing bacterial cell killing, membrane damage, and lipid peroxidation. As a strict anaerobic bacterium, when P. melaninogenica is exposed to oxygen, it produces hydrogen peroxide and superoxide and induces 8OHdG (8-hydroxy-2'-deoxyguanosine) which indicates that hydrogen peroxide induces oxidative DNA damage in the system. However, during oxygen exposure, vitamin C produces hydrogen peroxide and induced 8OdHG formation which indicates that even though hydrogen peroxide is permeable to the membrane, it does not have direct relationship with DNA. Vitamin C is a reducing agent which is able to replace superoxide in reducing Iron(II) and Iron (III) and encourage the formation of hydroxyl radical. This shows definite interaction with iron. The results indicate that vitamin C enhances oxygen-induced 8OHdG formation only in acidic conditions; therefore, when the local condition is acidic, vitamin C turns out to act as a pro-oxidant by reducing free iron. This research concluded that vitamin C enhances the survival of cells with DNA damage. Vitamin C suppressed the oxygen-induced death of bacterial cells and membrane damage which leads to cell death and also suppressed lipid peroxidation which leads to membrane damage. The new information found in this research this that vitaminc C finds singlet oxygen which forms reactive oxygen species. The presence of both, catalase and vitamic C greatly suppresses cell killing. Now it is known that vitamin C shows both pro-oxidative activity by enhancing the oxidative DNA damage and antioxidative activity by decreasing cell death, membrane damage, and lipid peroxidation due to oxygen exposure.
1. Yanagisawa, M., Kuriyama, T., Williams, D., Nakagawa, K., Karasawa, T. “Proteinase Activity of Prevotella Species Associated with Oral Purulent Infection.” CURRENT MICROBIOLOGY. 2006 . Vol. 52. pp. 375–378
2. Shi, M., Xu, B., Azakami, K., Morikawa, T., Watanabe, K., Morimoto, K., Komatsu, M., Aoyama, K., & Takeuchi, T. “Dual role of vitamin C in an oxygen-sensitive system: Discrepancy between DNA damage and dell death.” Free Radical Research, February 2005; 39(2): pp. 213–220
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8. http://www.ncbi.nlm.nih.gov/sites/entrez?db=genome&cmd=search&term=Prevotella %20melaninogenica
9. A. Rajasuo1, K. Perkki, S. Nyfors, H. Jousimies-Somer, and J.H. Meurman “Bacteremia Following Surgical Dental Extraction with an Emphasis on Anaerobic Strains.” J Dent Res, 2004, 83(2): pp. 170-174
Edited by Min Kyung Kim, student of Rachel Larsen
Edited by KLB