Fusobacterium polymorphum is a subspecies strain of the anaerobic, Gram-negative bacterium, Fusobacterium nucleatum.^[1] Originally, it was isolated from the plaque samples of individuals diagnosed with periodontitis and has been phylogenetically identified as its own distinct sub-group, separate from its previously studied sister strains.^[2][3] Research studies have also linked this subspecies to human diseases, such as fatal sepsis and inflammatory periodontal disease.^[4][5]

Fusobacterium polymorphum
Scientific classification
Domain:	Bacteria
Kingdom:	Fusobacteriati
Phylum:	Fusobacteriota
Class:	Fusobacteriia
Order:	Fusobacteriales
Family:	Fusobacteriaceae
Genus:	Fusobacterium
Species:	F. nucleatum
Binomial name
Fusobacterium nucleatum Knorr, 1922
Subspecies
F. polymorphum

Taxonomy and Phylogeny

Fusobacterium polymorphum is a subspecies of Fusobacterium nucleatum, which is a member of the phylum Fusobacteriota and family Fusobacteriaceae.^[1] Having originally been grouped together with Bacteroides, as well as other Gram-negative anaerobes, advances in genetic analysis have made it clear that Fusobacterium are actually phylogenetically closer in relation to organisms such as those of the genus Leptotrichia.^[6] Additionally, with the complete genome sequencing of the core species, F. nucleatum, it has been discovered that approximately 35-56% of Fusobacterium genes likely have been acquired from Bacteroidetes, Proteobacteria, Spirochaetes, and Firmicutes, as a result of horizontal gene transfer.^[6] More specifically, further analysis has led to suggestions that the genes responsible for coding Fusobacterium's Gram-negative cell wall, may have origins tracing back to Proteobacteria.^[6]

Discovery

Physiology

F. polymorphum, like all other subspecies of F. nucleatum, is a bacillus-shaped, Gram-negative anaerobic microbe.^[3][10] It has been found that optimum growth for F. polymorphum is at around a pH of 7.4, with a generation time of 3.5 hours.^[11] However, it was discovered that this optimum growth rate was only applicable in cultures that were limited in glucose, histidine, and serine.^[11]

Ecology

Fusobacterium polymorphum, along with its sister subspecies, is readily found within the plaque of human teeth, as well as within periodontal pockets, being one of the many bacteria within the oral microbiota involved in the inflammation of the gums.^[10] On top of this, F. polymorphum has also been found to inhabit areas of the gastrointestinal tract, making it closely associated with intestinal inflammation and inflammatory bowel disease.^[12] Nonetheless, in most instances, the mere presence of F. polymorphum within the human body is harmless and does not always lead to the development of disease, as it is an organism that has been commonly found in the mouths of healthy individuals.^[1] There is the possibility of this strain becoming opportunistic in certain microbial environments, which could potentially result in its increased proliferation and eventual progression towards a number of systemic diseases.^[1]

Genomics

Genome sequencing has revealed that F. nucleatum ssp. polymorphum (FNP) has about 2.4 million base pairs in its individual chromosome and 11,934 base pairs in its plasmid, making it about 300 thousand base pairs larger than its sister strain F. nucleatum ssp. nucleatum (FNN), which has a genome consisting of approximately 2.1 million base pairs.^[3] When comparing F. polymorphum's genome with those of other subspecies, it was found that about 38% of its base pairs were either completely unique to F. polymorphum or shared by only one of the two other subspecies' genomes being studied.^[3] This is indicative of F. polymorphum's genetic uniqueness and suggests that it may possess certain characteristic differences than its sister subspecies, particularly in terms of its pathogenic properties.^[3] For instance, research found 132 predicted proteins that contributed to Fusobacterium's virulence, most of which, however, were found in the subspecies nucleatum and vincentii.^[3] In the case of F. polymorphum specifically, a few notably identified proteins included a VacJ homolog (FNP_0314), which has demonstrated high involvement in the transmission of Shigella flexneri within cells, MviN (FNP_1360), which is associated with the pathogenicity of Salmonella typhimurium, and VacB (FNP_1921), which is a ribonuclease that promotes the activation of virulent genes in Shigella flexneri.^[3]

Applications and Future Research

Further research into the subspecies, Fusobacterium polymorphum, is critical in nature, because of the health issues Fusobacterium nucleatum has been known to cause.^[1] For starters, it is well known that F. nucleatum is a prominent microbe that contributes to the occurrence of periodontitis, an infection of the gums.^[1] On top of this, it has been found that F. nucleatum has been able to travel across the human body and begin to inhabit different variants of tissue, potentially leading to the development of diseases, such as atherosclerosis, diabetes, and a wide variety of respiratory conditions.^[1] Given that there are a total of 5 subspecies within F. nucleatum, it is currently unclear whether there is a single specific subspecies that is primarily contributing to all of these disease-related complications, or if each subspecies contributes to its own set of systemic diseases.^[1] Therefore, further studying of this organism of interest, Fusobacterium polymorphum, would better allow for researchers to attain a better understanding for identifying and establishing specific linkages between our selected subspecies and the plethora of health issues that arise from the general species it falls under.^[1] Moreover, this increase in research would potentially enable scientists to discover new methods for reducing the growth and proliferation of this microbe through perhaps new means of oral hygiene, for instance, before further development causes any severe damage to the human body.^[1]

References