Abstract
Colorectal cancer (CRC) ranks second in cancer-related mortality and third in incidence, with an estimated 1.9 million new cases and over 900,000 deaths in 2020. Over the last two decades, Fusobacterium nucleatum, a Gram-negative pathobiont, has consistently been associated with CRC. However, not all subspecies exhibit the same behaviour or degree of association. Among them, F. nucleatum subspecies animalis (Fna) has emerged as the primary candidate, yet the functional basis underlying this association remains poorly defined.In this study, an integrated bioinformatic and experimental framework was employed to dissect genomic and functional variation among Fna strains relevant to CRC. Pangenomic analyses revealed an open pangenome and extensive heterogeneity in virulence factors across the species, including FadA and type V secretion system (T5SS; T5aSS-T5dSS) proteins, also known as autotransporters. A putative novel T5aSS was also identified, with its distribution varying across the genus. Functional assays demonstrated marked strain-specific differences in aggregation, biofilm formation, and host-cell interactions, with opposing trends of bacterial invasion and epithelial cell migration between HT29 and HCT116 cells. Notably, Fna strains enhanced cell migration in HT29 cells, but exhibited greater invasion in HCT116. Furthermore, this study provided the first evidence of an arginine- and galactose-inhibitable interaction between Fna and enterotoxigenic Bacteroides fragilis, highlighting the ecological and functional plasticity of Fna.
Collectively, these findings emphasise the functional significance of interstrain variability and the challenges of linking genotype to phenotype in a subspecies with a large accessory genome. This work establishes an empirical foundation for future investigations into the variable virulence repertoire of Fna and its polymicrobial interactions in CRC. By bridging microbiology and oncology, we highlight the potential for therapeutic strategies targeting not only malignant cells but also the microbial components that sustain them.
| Date of Award | 17 Mar 2026 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Darryl J Hill (Supervisor) & Adam Christian Chambers (Supervisor) |
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