Lack of Polynucleotide Phosphorylase activity in Enterococcus faecalis 14 increases the stability of EntDD14 bacteriocin transcripts

A mutant deficient in polynucleotide phosphorylase (PNPase) activity was previously constructed in Enterococcus faecalis 14; a strain producing a leaderless two-peptide bacteriocin, named enterocin DD14 (EntDD14). Here, we examined the impact of the absence of PNPase on the expression and synthesis of EntDD14, at the transcriptional and functional levels. Consequently, synthesis of EntDD14 started after only 3 h of growth at 37ºC and reached its highest level after 9 h, in both E. faecalis 14 and its isogenic PNPase deficient ( ΔpnpA ), and has remarkably increased at least two-fold in the ΔpnpA mutant. Notably, high expression level of the ddABCDEFGHIJ cluster was registered in ΔpnpA mutant. Transcriptional and in silico analyses support the existence of ddAB and ddCDEFGHIJ independent transcripts, and analysis of the fate of ddAB and ddCDEFGHIJ mRNAs indicated that the differences in mRNA levels and the high EntDD14 activity are likely due to a better stability of the two transcripts in the ΔpnpA mutant, which should result in a higher translation efficiency of the ddAB EntDD14 structural genes and their other protein determinants. Consequently, this study shows a potential link between the mRNA stability and EntDD14 synthesis, secretion and immunity in a genetic background lacking PNPase.