Fusobacterium nucleatum
A Microbial Biorealm page on the genus Fusobacterium nucleatum
Classification
Higher order taxa
root; cellular organisms; Bacteria; Fusobacteria; Fusobacteria (class); Fusobacteriaceae; Fusobacterales; Fusobacterium
Genus
Fusobacterium
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NCBI: Taxonomy |
Description and significance
Fusobacterium nucleatum is a bacterium that is commonly found in the dental plaque of humans and is frequently associated with gum disease. It is a key component of periodontal plaque due to its abundance and its ability to coaggregate with other species in the oral cavity. The cells of F. nucleatum are fusiform rods or spindle-shaped of many different lengths. In fact, the name refers to the organism as a small spindle-shaped rod. F. nucleatum is found in the dental plaque of many primates, thus includes man. This bacteria has been experimented to play a central role in dental plaque formation. This is due to its ability to adhere to a wide range of both Gram-positive and Gram-negative plaque microorganisms, such as Porphyromonas gingivalis. F. nucleatum is very much associated with periodontitis, along with invasive human infections of the head and neck, chest, lung, liver and abdomen. Due to its adherence ability, it can be associated with viruses, which adhere to host tissue cells as an invasion and modulate the host's immune response.
The pathogenic potential of Fusobacterium nucleatum and its significance in the development of periodontal diseases, as well as in infections in other organs, have gained new interest for several reasons. First, this bacterium has a very high chance to be pathogenic because of its high frequency in periodontal lesions, its production of irritants that affect the tissue, its ability to share synergisms with other bacteria in mixed infections, and its ability to form numerous aggregates with other suspected pathogens in periodontal disease(therefore, it acts as a bridge between early and late colonizers on surfaces of teeth). Second, F. nucleatum is the most common in clinical infections of other body sites. Third, recent new techniques have made it possible to obtain more information about F. nucleatum on the genetic level, thereby also gaining better knowledge of the structure and functions of the outer membrane proteins, which are of great interest with respect to coaggregation, cell nutrition, and antibiotic susceptibility.
Genome structure
Fusobacterium nucleatum is a Gram negative bacterium that does not create spores and is not motile. This bacterium has a G-C content of about 27 to 28 mol%. Its genome size is about 2.4 x 10^6 base pairs (bp). All in all, colony morphology is not a consistent parameter of F. nucleatum. Therefore, it is not sufficient for species identification.
Through phylogenetic grouping through analysis of the 16s rRNA sequences, F. nucleatum was found to be closely related to Bacteroides and the flavobacteria. Similarities have been found with F. nucleatum and the other two species with regards to its DNA and its antigenic composition. In addition, F. nucleatum is found to exhibit high levels of homology with F. alocis, F. periodonticum, and F. simiae. All these organisms, along with F. nucleatum, colonize in oral cavities.
Native plasmids have been identified in strains of F. nucleatum. Using one of the native plasmid pFN1, a F. nucleatum - E. coli shuttle vector has been developed.
Cell structure and metabolism
This organism is possesses an outer membrane, which is very much expected from a Gram negative bacterium. In addition, the bacterium also has a periplasmic space made of the peptidoglycan layers, in-between the inner and outer cytoplasmic membranes. The inner-membrane is made of a symmetrical phospholipids bilayer with proteins and phospholipids in equal amounts. The outer-membrane, on the other hand, is an asymmetric membrane containing phospholipids, lipopolysaccharides (LPS), lipoproteins, and proteins. It functions as a molecular sieve. The LPS contains 3-deoxy-D-manno-octulosonic acid. Due to the large amount of proteins present in the outer-membrane, it was found that a third of the weight of this bacterium is due to the proteins present in the outer-membrane.
In addition, with its numerous numbers of proteins on the outer cell surface, the bacterium could be found having specific interactions with various complementary structures on the host cell surface. This adherence is mediated by the protein known as Adhesin. This adherence is very important in the colonization and establishment of the infection in a susceptible host. In general, adherence is very important to this organisms’ pathogenicity. F. nucleatum plays an important role in adhesion and coaggregation reactions found in periodontal pockets. LPS extracts from F. nucleatum helps alongside Adhesin to provide adhesion to the saliva-filled environment. All in all, this characteristic is very important to the survival and susceptibility of the F. nucleatum since fusobacteria adhere very poorly to human cheek epithelial cells. With all these in mind, it is obvious to why research of the bacterium’s adherence proteins: Outer Membrane Proteins (OMP) is currently being conducted.
Due to its non-motile nature, it has been found that F. nucleatum does not possess pili or flagellae. It does, however, possess a mucopolysaccharide capsule surrounding the organism of variable thickness, which may be very important to the organism’s pathogenic capabilities.
This bacterium is an anaerobic creature that grows in an environment with only up to 6% oxygen saturation, and also requires a media containing Trypticase, peptone, or yeast extract. This organism’s ability to produce butyric acid as a major product of fermentation of glucose and peptone is what differentiates Fusobacterium species from other gram-negative, non-sporing rod-shaped bacterium. F. nucleatum is one of the few non-sporulating anaerobic species that utilize amino acid catabolism to provide energy. This organism also utilizes glutamate, histadine, and aspartate. Apparently, F. nucleatum does not utilize glucose as its main energy source. Available data indicate that glucose instead is used for the biosynthesis of intracellular molecules and not energy metabolism. This unusual characteristic has been the focus of interest of several studies.
Ecology
Fusobacterium nucleatum inhabits the mucous environment of an animal oral cavity, serving as a pathogen. It is a predominant member of the human oral flora. Because of its pathogenic and parasitic nature, Fusobacterium nucleatum does not affect the environment directly. However, it may alter the ecosystem by its effects on the population of infected host animals. This bacterium has a significant impact on the ecology of the oral cavity due to its ability to adhere to many different microbial species and itself. F. nucleatum is a major component of subgingival plaque.
Pathology
How does this organism cause disease? Human, animal, plant hosts? Virulence factors, as well as patient symptoms.
Application to Biotechnology
Aminopeptidase is nutritionally very important for Fusobacterium nucleatum. This peptidase is found to be cell-associated by isolating the culture from disrupted chemostat-grown cells. The enzyme was inactivated by chelators, bestatin, phydroxymercuribenzoate and some heavy metals. Aminopeptidase, therefore, appears to be a cobalt-activated metallo-peptidase. Together with other peptidases, Aminopeptidase would be vital to the growth and survival, in the subgingival environment of the mouth, of F. nucleatum.
A Fusobacterium nucleatum shuttle plasmid, pHS17, capable of transforming E. coli and F. nucleatum ATCC10953, was constructed with pFN1. Shuttle plasmid pHS17 was stably maintained in the F. nucleatum transformants. The differences in the transformation efficiencies suggested the presence of a restriction-modification system in Fusobacterium nucleatum.
Fusobacterium nucleatum ATCC23726 is one type of Fusobacterium nucleatum that is still having its full assembly in progress.
Current Research
Enter summaries of the most recent research here--at least three required
References
Edited by Jason Homan, student of Rachel Larsen and Kit Pogliano
