<i>Fusobacterium sphaericum</i> sp. nov., isolated from a human colon tumor adheres to colonic epithelial cells and induces IL-8 secretion

Cancerous tissue is a largely unexplored microbial niche that provides a unique environment for the colonization and growth of specific bacterial communities, and with it, the opportunity to identify novel bacterial species. Here, we report distinct features of a novel <i>Fusobacterium</i> species, <i>F.</i> <i>sphaericum</i> sp. nov. (<i>Fs</i>), isolated from primary colon adenocarcinoma tissue. We acquire the complete closed genome and associated methylome of this organism and phylogenetically confirm its classification into the <i>Fusobacterium</i> genus, with <i>F. perfoetens</i> as its closest neighbor. <i>Fs</i> is phenotypically and genetically distinct, with morphological analysis revealing its coccoid shape, that while similar to <i>F. perfoetens</i> is rare for most <i>Fusobacterium</i> members. <i>Fs</i> displays a metabolic profile and antibiotic resistance repertoire consistent with other <i>Fusobacterium</i> species. <i>In vitro, Fs</i> has adherent and immunomodulatory capabilities, as it intimately associates with human colon cancer epithelial cells and promotes IL-8 secretion. An analysis of the prevalence and abundance of <i>Fs</i> in > 20,000 human metagenomic samples shows that it is a rarely detected member within human stool with variable relative abundance, found in both healthy controls and patients with colorectal cancer (CRC). Our study sheds light on a novel bacterial species isolated directly from the human CRC tumor niche and given its <i>in</i> <i>vitro</i> interaction with cancer epithelial cells suggests that its role in human health and disease warrants further investigation.