Functional redundancy of translation-associated factors masks the role of YebC2 in Enterococcus faecalis

Enterococcus faecalis has two YebC paralogs, yebC1_EF (EF0663) and yebC2_EF (EF2866), with distinct roles. While yebC1_EF encodes a transcriptional regulator, yebC2_EF was recently implicated in resolving ribosome stalling. Our informatic analysis of transcriptomic data revealed yebC2_EF as a potential virulence-associated candidate in E. faecalis. This gene is transcribed from a putative consensus vegetative promoter with conserved - 10 (TATAAT) and - 35 (TTaACA) boxes separated by 17 nucleotides, and ends at a Rho-independent terminator. To examine the role of yebC2_EF, an insertion mutant strain (JH2866) was constructed using the thermosensitive plasmid pGhost9. Phenotypic analysis showed no significant differences in growth or survival between wild-type and yebC2-defective strains under standard or stressful conditions. Similarly, virulence assays in Galleria mellonella larvae showed no attenuation, suggesting that yebC2_EF does not play a major role in virulence under the tested conditions. In addition, in this study, we found orthologs of YebC2 in all Enterococcus species, while yebC1 is lost in 20% of them. This fact suggests a major role of yebC2 in this genus. Even though inactivation of yebC2_EF had no discernible impact on the physiology or virulence of E. faecalis, this may be due to functional redundancy with other translation factors such as EF-P (translation elongation factor P, EF0287) and YfmR (ABCF ATPase YfmR/Uup, EF1575). As in the related microorganisms Bacillus subtilis and Streptococcus pyogenes, these factors can compensate for the loss of YebC2.