The respiratory enzyme complex Rnf is vital for metabolic adaptation and virulence inFusobacterium nucleatum

Abstract

ABSTRACTA prominent oral commensal and opportunistic pathogen,Fusobacterium nucleatumcan 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 Rnf complex, encoded by thernfCDGEABgene cluster, is key to fusobacterial metabolic adaptation and virulence. Genetic disruption of the Rnf complex via non-polar, in-frame deletion ofrnfC(ΔrnfC) 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 ΔrnfCcells restores coaggregation, while addition of lysine inhibits this process. These phenotypes mirror that of a mutant (ΔkamA) that fails to metabolize extracellular lysine. Strikingly, the ΔrnfCmutant is defective in ATP production, cell growth, cell morphology, and expression of the enzyme MegL that produces hydrogen sulfide from cysteine. Targeted metabolic profiling demonstrated that catabolism of many amino acids, including histidine and lysine, is altered in ΔrnfCcells, thereby reducing production of ATP and metabolites including H2S and butyrate. Most importantly, we show that the ΔrnfCmutant 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.IMPORTANCEAlthough viewed as an oral commensal, the Gram-negativeF. nucleatumis an opportunistic pathogen that can spread to extra-oral sites such as placenta and colon, promoting adverse pregnancy outcomes and colorectal cancer, respectively. How this anaerobe sustains various metabolically changing environments enabling its virulence potential remains unclear. We demonstrate here that the highly conserved Rnf complex is key to fusobacterial metabolic adaptation and virulence. Genetic disruption of this Rnf complex causes global defects in polymicrobial interaction, biofilm formation, cell growth and morphology, H2S production, and ATP synthesis. Targeted metabolomic profiling demonstrates that the loss of this respiratory enzyme significantly diminishes catabolism of numerous amino acids, which negatively impacts fusobacterial virulence as tested in a preterm birth model in mice.