The absence of PNPase activity in Enterococcus faecalis results in alterations of the bacterial cell-wall but induces high proteolytic and adhesion activities

Enterococci are lactic acid bacteria (LAB) used as starters and probiotics, delineating their positive attributes. Nevertheless, enterococci can be culprit for thousands of infectious diseases, including urinary tract infections, bacteremia and endocarditis. Here, we aim to determine the impact of polynucleotide phosphorylase (PNPase) in the biology of Enterococcus faecalis 14; a human isolate from meconium. Thus, a mutant strain deficient in PNPase synthesis, named delta pnpA mutant, was genetically obtained. After that, a transcriptomic study revealed a set of 244 genes differentially expressed in the delta pnpA mutant compared with the wild-type strain, when exploiting RNAs extracted from these strains after 3 and 6 h of growth. Differentially expressed genes include those involved in cell wall synthesis, adhesion, biofilm formation, bacterial competence and conjugation, stress response, transport, DNA repair and many other functions related to the primary and secondary metabolism of the bacteria. Moreover, the delta pnpA mutant showed an altered cell envelope ultrastructure compared with the WT strain, and is also distinguished by a strong adhesion capacity on eukaryotic cell as well as a high proteolytic activity. This study, which combines genetics, physiology and transcriptomics enabled us to show further biological functions that could be directly or indirectly controlled by the PNPase in E. faecalis 14.

Automated summary

This study investigated the role of polynucleotide phosphorylase (PNPase) in the biology of Enterococcus faecalis 14. By obtaining a mutant strain deficient in PNPase synthesis, the researchers found that differentially expressed genes, altered cell envelope ultrastructure, enhanced adhesion capacity on eukaryotic cells, and increased proteolytic activity were observed in the delta pnpA mutant compared to the wild-type strain. These findings suggest that PNPase may directly or indirectly control various biological functions in E. faecalis 14.