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.
Highlights
IntroductionMost bacteria live within complex microbial communities in which they must compete for biotic and abiotic resources to ensure their survival
E. faecalis strains JH2-2 and JH2-2, and the set of Tn5 mutants were cultured in Trypticase Soy Broth (TSB) or Trypticase Soy Agar (TSA) with chloramphenicol (20 μg/mL) to avoid plasmid curing during their growth
In addition to the role of the resistance genes in self-immunity, the present results show that they can act against several types of antimicrobials and may produce different degrees of resistance to both closely and distantly related bacteria
Summary
Most bacteria live within complex microbial communities in which they must compete for biotic and abiotic resources to ensure their survival. This competition can be passive, when one strain harms another through resource consumption, or active, when strains damage each other through chemical warfare (antagonistic interaction) [1]. An important antagonistic mechanism in bacteria involves the production of antimicrobial peptides (bacteriocins), a widely observed phenomenon [2]. Bacteriocin production has been observed in cyanobacteria [3], enterobacteria [4], and lactic acid bacteria (LAB) [5], among many other prokaryotes and Archaea. Bacteriocin production allows bacteria to improve the stability of their communities by competing against closely related bacterial species to establish a stable niche for the producer strain [6]
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