The Respiratory Enzyme Complex Rnf is Vital for Metabolic Adaptation and Virulence in Fusobacterium Nucleatum

The Gram-negative oral pathobiont Fusobacterium nucleatum can traverse to extra-oral sites such as placenta and colon, promoting adverse pregnancy outcomes and colorectal cancer, respectively. How this anaerobe sustains many metabolically changing environments enabling its virulence potential remains unclear. Informed by our genome-wide transposon mutagenesis, we report here that the highly conserved Rhodobacternitrogen-fixation (Rnf) complex, encoded by the rnfCDGEAB gene cluster, is key to fusobacterial metabolic adaptation and virulence. Genetic disruption of the Rnf complex via non-polar, in-frame deletion of rnfC (Delta rnfC) abrogates polymicrobial interaction (or coaggregation) associated with adhesin RadD and biofilm formation. The defect in coaggregation is not due to reduced cell surface of RadD, but rather an increased level of extracellular lysine, which binds RadD and inhibits coaggregation. Indeed, removal of extracellular lysine via washing Delta rnfC cells restores coaggregation, while addition of lysine inhibits this process. These phenotypes mirror that of a mutant (Delta kamA) that fails to metabolize extracellular lysine. Strikingly, the Delta rnfC mutant is defective in ATP production, cell growth, cell morphology, and expression of the enzyme MegL that produces hydrogen sulfide (H2S) from cysteine. Targeted metabolic profiling demonstrated that catabolism of many amino acids, including histidine and lysine, is altered in Delta rnfC cells, thereby reducing production of ATP and metabolites including H2S and butyrate. Most importantly, we show that the Delta rnfC mutant is severely attenuated in a mouse model of preterm birth. The indispensable function of Rnf complex in fusobacterial pathogenesis via modulation of bacterial metabolism makes it an attractive target for developing therapeutic intervention.