AUTHOR=Ladjouzi Rabia , Lucau-Danila Anca , Benachour Abdellah , Drider Djamel 

TITLE=A Leaderless Two-Peptide Bacteriocin, Enterocin DD14, Is Involved in Its Own Self-Immunity: Evidence and Insights

JOURNAL=Frontiers in Bioengineering and Biotechnology

VOLUME=8

YEAR=2020

URL=https://www.frontiersin.org/journals/bioengineering-and-biotechnology/articles/10.3389/fbioe.2020.00644

DOI=10.3389/fbioe.2020.00644

ISSN=2296-4185

ABSTRACT=<p>Enterocin DD14 (EntDD14) is a two-peptide leaderless bacteriocin produced by <italic>Enterococcus faecalis</italic> 14, a strain previously isolated from meconium. EntDD14 has a strong antibacterial activity against Gram-positive bacteria. Leaderless bacteriocins, unlike bacteriocins with leader peptides, are immediately active after their translation, and a producing strain has then to develop specific mechanisms to protect both intra and extracellular compartments. The <italic>in silico</italic> analysis of <italic>Ent. faecalis</italic> 14 genome allowed to locate downstream of structural <italic>ddAB</italic> genes, 8 other adjacent genes, designed <italic>ddCDEFGHIJ</italic>, which collectively may form three operons. To gain insights on immunity mechanisms of <italic>Ent. faecalis</italic> 14, mutant strains knocked out in <italic>ddAB</italic> genes encoding bacteriocin precursor peptides (Δ<italic>bac</italic>) and/or ABC transporter (Δ<italic>ddI</italic>) of EntDD14 were constructed and characterized. Importantly, Δ<italic>bac</italic> mutant strains, from which structural <italic>ddAB</italic> genes were deleted, resulted unable to produce EntDD14 and sensitive to exogenous EntDD14 showing their involvement in the <italic>Ent. faecalis</italic> 14 immunity system. Moreover, the sensitivity of Δ<italic>bac</italic> mutants appeared not to be associated with the down-regulation of <italic>ddCDEFGHIJ</italic> gene expression since they were similarly expressed in both Δ<italic>bac</italic> and wild-type strains during the log phase while they were found significantly down-regulated in the Δ<italic>bac</italic> mutant strain after 24 h of growth. Data gathered from this study suggest also the implication of the ABC transporter (<italic>ddHIJ</italic>) in the active export of EntDD14 but ruled-out its involvement in the primary self-immunity system. Interestingly, non-bacteriocin producing <italic>Ent. faecalis</italic> JH2-2 cells transformed with <italic>ddAB</italic>, or <italic>ddAB</italic> plus genes encoding the ABC transporter (<italic>ddAB-HIJ</italic>) did not produce EntDD14 and remained sensitive to its action. Of note, trans-complementation of the Δ<italic>bac</italic> mutant strain with these constructions allowed to recover the WT phenotype. To the best of our knowledge, this is the first study delineating the role of the intracellular two-peptide leaderless bacteriocins in their self-immunity.</p>