Enterocin Cross-Resistance Mediated by ABC Transport Systems

Abstract

In their struggle for life, bacteria frequently produce antagonistic substances against competitors. Antimicrobial peptides produced by bacteria (known as bacteriocins) are active against other bacteria, but harmless to their producer due to an associated immunity gene that prevents self-inhibition. However, knowledge of cross-resistance between different types of bacteriocin producer remains very limited. The immune function of certain bacteriocins produced by the Enterococcus genus (known as enterocins) is mediated by an ABC transporter. This is the case for enterocin AS-48, a gene cluster that includes two ABC transporter-like systems (Transporter-1 and 2) and an immunity protein. Transporter-2 in this cluster shows a high similarity to the ABC transporter-like system in MR10A and MR10B enterocin gene clusters. The aim of our study was to determine the possible role of this ABC transporter in cross-resistance between these two different types of enterocin. To this end, we designed different mutants (Tn5 derivative and deletion mutants) of the as-48 gene cluster in Enterococcus faecalis and cloned them into the pAM401 shuttle vector. Antimicrobial activity assays showed that enterocin AS-48 Transporter-2 is responsible for cross-resistance between AS-48 and MR10A/B enterocin producers and allowed identification of the MR10A/B immunity gene system. These findings open the way to the investigation of resistance beyond homologous bacteriocins.

Circular and L50-like leaderless enterocins share a common ABC-transporter immunity gene

“…This last function explains the frequent presence of ABC transporters as immunity genes in several bacteriocins. This is the case for the Mr10EFGH ABC transporter associated with the enterocins MR10A/B, which is also found in AS-48 producers and is involved in their cross-resistance [ 22 ]. According to the present findings, this transporter is also shared by other bacteriocins of the uberolysin/carnocyclin family and by some orphan strains of the enterocin structural gene (Fig.…”

“…Our group previously reported cross-resistance between E. faecalis MRR10-3 and E. faecalis A-48-32 [ 22 ], which produce bacteriocins of distinct classes, i.e., enterocins MR10A/B (class II- not posttranslationally modified) and enterocin AS-48 (class I- circular posttranslationally modified), respectively. Both strains share a homologous ABC-type transport system (Mr10EFGH and As-48EFGH, respectively) involved in self-immunity and cross-resistance [ 22 ].…”

“…Our group previously reported cross-resistance between E. faecalis MRR10-3 and E. faecalis A-48-32 [ 22 ], which produce bacteriocins of distinct classes, i.e., enterocins MR10A/B (class II- not posttranslationally modified) and enterocin AS-48 (class I- circular posttranslationally modified), respectively. Both strains share a homologous ABC-type transport system (Mr10EFGH and As-48EFGH, respectively) involved in self-immunity and cross-resistance [ 22 ]. AS-48 has an additional ABC transporter downstream the As-48EFGH transporter [ 23 ], and a second transporter involving pleckstrin homology domains was recently described in L50-like enterocins downstream the Mr10EFGH transporter [ 24 ], but only the As-48EFGH and Mr10EFGH transporters show similarity between the transporters present on both enterocin gene clusters [ 22 ].…”

“…Both strains share a homologous ABC-type transport system (Mr10EFGH and As-48EFGH, respectively) involved in self-immunity and cross-resistance [ 22 ]. AS-48 has an additional ABC transporter downstream the As-48EFGH transporter [ 23 ], and a second transporter involving pleckstrin homology domains was recently described in L50-like enterocins downstream the Mr10EFGH transporter [ 24 ], but only the As-48EFGH and Mr10EFGH transporters show similarity between the transporters present on both enterocin gene clusters [ 22 ]. ABC transporters are widespread in multiple organisms and generally comprise four core domains: two transmembrane domains (TMDs) and two hydrophilic and peripheral cores, where Walker A and Walker B motifs and the C-loop and the D-loop (two hallmarks of transporters) are associated with the cytoplasmic surface of the membrane [ 25 ].…”

Advances in the preclinical characterization of the antimicrobial peptide AS-48

“…So far, the only genetically encoded resistance to AS-48 is provided by the presence of the immunity protein (As-48D1) and the ABC-transporter (As-48EFGH) which are encoded by the as-48 operon (Martínez-Bueno et al, 1998;Diaz et al, 2003). This transporter is also related to resistance to other similar bacteriocins (Teso-Pérez et al, 2021). Only AS-48 producer strains are fully resistant to the peptide, while the (heterologous) expression of them in other organisms provides partial levels of resistance (Martínez-Bueno et al, 1998;Fernández et al, 2007).…”