Genome-wide analysis of Enterococcus faecalis genes that facilitate interspecies competition with Lactobacillus crispatus

Enterococci are opportunistic pathogens notorious for causing a variety of infections. While both Enterococcus faecalis and Lactobacillus crispatus are commensal residents of the vaginal tract, the molecular mechanisms that enable E. faecalis to outcompete L. crispatus, and consequently cause vaginal infections remains unknown. To begin to address this, we need to gain a better understanding of the competitive interactions between E. faecalis and L. crispatus. Here, we show that L. crispatus eradicates E. faecalis in a contact-independent manner. Using transposon sequencing to identify E. faecalis OG1RF transposon (Tn) mutants that are either under-represented or over-represented when co-cultured with L. crispatus, we found that Tn mutants with disruption in the dltABCD operon, that encodes the biosynthetic pathway for D-alanylation of teichoic acids, and OG1RF_11697 encoding for an uncharacterized hypothetical protein are more susceptible to killing by L. crispatus. Inversely, Tn mutants with disruption in ldh1, that encodes for L-lactate dehydrogenase, are more resistant to L. crispatus killing. Using the Galleria mellonella infection model, we show that co-injection of L. crispatus with E. faecalis OG1RF enhances larvae survival while this L. crispatus-mediated protection was lost in larvae co-infected with either L. crispatus and E. faecalis {Delta}ldh1 or {Delta}ldh1{Delta}ldh2 strains. Last, using RNA sequencing to identify E. faecalis genes that are differently expressed in the presence of L. crispatus, we found major changes in expression of genes associated with glycerophospholipid metabolism, central metabolism and general stress responses. The findings in this study provide insights on how E. faecalis mitigate assaults by L. crispatus. IMPORTANCEEnterococcus faecalis is an opportunistic pathogen notorious for causing a multitude of infections. While E. faecalis must compete with Lactobacillus crispatus to cause vaginal infections, how E. faecalis overcomes L. crispatus killing remains unknown. We show that L. crispatus eradicates E. faecalis temporally in a contact-independent manner. Using high throughput molecular approaches, we identified genetic determinants that enable E. faecalis to compete with L. crispatus. This study represents an important first step for the identification of adaptive genetic traits required for enterococci to compete with lactobacilli.