Evolution of Invasion in a Diverse Set of Fusobacterium Species

Abstract

The diverse Fusobacterium genus contains species implicated in multiple clinical pathologies, including periodontal disease, preterm birth, and colorectal cancer. The lack of genetic tools for manipulating these organisms leaves us with little understanding of the genes responsible for adherence to and invasion of host cells. Actively invading Fusobacterium species can enter host cells independently, whereas passively invading species need additional factors, such as compromise of mucosal integrity or coinfection with other microbes. We applied whole-genome sequencing and comparative analysis to study the evolution of active and passive invasion strategies and to infer factors associated with active forms of host cell invasion. The evolution of active invasion appears to have followed an adaptive radiation in which two of the three fusobacterial lineages acquired new genes and underwent expansions of ancestral genes that enable active forms of host cell invasion. Compared to passive invaders, active invaders have much larger genomes, encode FadA-related adhesins, and possess twice as many genes encoding membrane-related proteins, including a large expansion of surface-associated proteins containing the MORN2 domain of unknown function. We predict a role for proteins containing MORN2 domains in adhesion and active invasion. In the largest and most comprehensive comparison of sequenced Fusobacterium species to date, we have generated a testable model for the molecular pathogenesis of Fusobacterium infection and illuminate new therapeutic or diagnostic strategies.

Fusobacterium nucleatum: a commensal-turned pathogen

“…Invasion of endothelial cells by F. nucleatum in mouse placenta has been observed [51]. The invasiveness of F. nucleatum varies widely among different strains, and has been shown as directly related to the IBD disease status [77,97]. …”

Cancer‐associated fecal microbial markers in colorectal cancer detection

“…F. nucleatum has been found in higher levels in CRC, and adenomas, compared to adjacent normal tissue . It is a highly adhesive bacterial species and has the ability to invade colonic epithelial cells . Additionally, recent studies showed that, in human CRC, high amounts of F. nucleatum in tumor tissue is correlated to low infiltration of T lymphocytes and poor patient prognosis …”

“…10,[23][24][25] It is a highly adhesive bacterial species and has the ability to invade colonic epithelial cells. 13,29 Additionally, recent studies showed that, in human CRC, high amounts of F. nucleatum in tumor tissue is correlated to low infiltration of T lymphocytes and poor patient prognosis. 30,31 In this study, we investigated the utility of microbial markers for clbA1 bacteria (clbA) and, afa-11 DAEC (afaC), and F. nucleatum, in CRC detection, using 238 human stool samples from the FECSU (the Faecal and Endoscopic Colorectal Study in Umeå) cohort.…”

Reevaluating the Fusobacterium Virulence Factor Landscape

“…Despite the extensive phylogenetic analysis of Fusobacterium and our increasing understanding of what is required to be a virulent strain, our knowledge of the specific virulence mechanisms remains limited. For instance, it was previously shown that multiple F. necrophorum and F. mortiferum strains were significantly more invasive than F. nucleatum strains into keratinocytes, which is in direct conflict with bioinformatic reports that place these species in the non-invasive or passively invasive category (24,25) . F. necrophorum and F. mortiferum are invasive but have not been associated with colorectal cancer, which raises an additional question of how virulence is truly regulated in this disease.…”

“…In a recent study, Fusobacterium species were bioinformatically divided into actively invading species ( F. nucleatum , F. periodonticum , F. varium , F. ulcerans ) ( Fig. 1C ), passively invading species that are believed to need a compromised epithelial barrier for cellular entry ( F. necrophorum , F. gonidiaformans ), and those with unknown invasive potential ( F. mortiferum ) (24) . Despite the extensive phylogenetic analysis of Fusobacterium and our increasing understanding of what is required to be a virulent strain, our knowledge of the specific virulence mechanisms remains limited.…”