Genetic and molecular determinants of polymicrobial interactions in Fusobacterium nucleatum

Abstract

A gram-negative colonizer of the oral cavity, Fusobacterium nucleatum not only interacts with many pathogens in the oral microbiome but also has the ability to spread to extraoral sites including placenta and amniotic fluid, promoting preterm birth. To date, however, the molecular mechanism of interspecies interactions—termed coaggregation—by F. nucleatum and how coaggregation affects bacterial virulence remain poorly defined. Here, we employed genome-wide transposon mutagenesis to uncover fusobacterial coaggregation factors, revealing the intertwined function of a two-component signal transduction system (TCS), named CarRS, and a lysine metabolic pathway in regulating the critical coaggregation factor RadD. Transcriptome analysis shows that CarR modulates a large regulon including radD and lysine metabolic genes, such as kamA and kamD, the expression of which are highly up-regulated in the ΔcarR mutant. Significantly, the native culture medium of ΔkamA or ΔkamD mutants builds up abundant amounts of free lysine, which blocks fusobacterial coaggregation with streptococci. Our demonstration that lysine-conjugated beads trap RadD from the membrane lysates suggests that lysine utilizes RadD as its receptor to act as a metabolic inhibitor of coaggregation. Lastly, using a mouse model of preterm birth, we show that fusobacterial virulence is significantly attenuated with the ΔkamA and ΔcarR mutants, in contrast to the enhanced virulence phenotype observed upon diminishing RadD (ΔradD or ΔcarS mutant). Evidently, F. nucleatum employs the TCS CarRS and environmental lysine to modulate RadD-mediated interspecies interaction, virulence, and nutrient acquisition to thrive in the adverse environment of oral biofilms and extraoral sites.

Resident microbes shape the vaginal epithelial glycan landscape

“…exposed Gal residues). For example, Fusobacterium nucleatum encodes multiple functionally characterized galactose-recognizing adhesins 91,92 and colonizes women with BV more often than women without BV 9,14 . The relative absence of sialic acids and exposure of galactose on the BV epithelium could therefore lead to improved colonization by F. nucleatum or other potential pathogens linked with BV.…”

Mucosal microbiomes and Fusobacterium genomics in Vietnamese colorectal cancer patients

“…We next sought to examine the presence of several Fusobacterium virulence factors, of which pathogenicity has been proven in experimental studies, including genes encoding adhesin ( fadA, cbpF ), lectin ( fap2 ), and bacterial co-aggregation factor ( radD ) [12,13,29,30]. RadD is an autotransporter facilitating Fusobacterium’s interspecies interaction in polymicrobial biofilms [30], while CbpF inhibits CD4 + T-cell response through CEACAM1 binding and activation [31]. Genomic screening showed that fap2 was present and intact in the majority of genomes from both species (49/53), with disruptive mutations occurring in some isolates, such as the tumour-associated F. nucleatum animalis in P46 (Figure 4A).…”

Colorectal cancer: the facts in the case of the microbiota

“…In contrast with Fap2, RadD and CmpA are considerably smaller adhesins that have predominantly been investigated for their roles in Fn's polymicrobial binding behavior (83,84). Potentially relevant to colorectal carcinogenesis as relates to colonic tumoral biofilms, Fn employs RadD to adhere to Clostridioides difficile and enhances C. difficile's extracellular polysaccharide production and biofilm formation (85).…”