Regulatory crosstalk between type I and type II toxin-antitoxin systems in the human pathogen Enterococcus faecalis

Abstract

We discovered a chromosomal locus containing 2 toxin-antitoxin modules (TAs) with an antisense transcriptional organization in the E. faecalis clinical isolate V583. These TAs are homologous to the type I txpA-ratA system and the type II mazEF, respectively. We have shown that the putative MazF is toxic for E. coli and triggers RNA degradation, and its cognate antitoxin MazE counteracts toxicity. The second module, adjacent to mazEF, expresses a toxin predicted to belong to the TxpA type I family found in Firmicutes, and the antisense RNA antidote, RatA. Genomic analysis indicates that the cis-association of mazEF and txpA-ratA modules has been favored during evolution, suggesting a selective advantage for this TA organization in the E. faecalis species. We showed regulatory interplays between the 2 modules, involving transcription control and RNA stability. Remarkably, our data reveal that MazE and MazEF have a dual transcriptional activity: they act as autorepressors and activate ratA transcription, most likely in a direct manner. RatA controls txpA RNA levels through stability. Our data suggest a pivotal role of MazEF in the coordinated expression of mazEF and txpA-ratA modules in V583. To our knowledge, this is the first report describing a crosstalk between type I and II TAs.

MazF activation promotes translational heterogeneity of thegrcAmRNA inEscherichia colipopulations

“…Taken together, our results suggest that MazF activation has a subtle effect in stressed bacterial populations during antibiotic treatment or amino acid starvation, which may further cross-activate other TA systems ( Kasari et al, 2013 ; Wessner et al, 2015 ) or stress response mechanisms ( Wang & Wood, 2011 ), collectively affecting bacterial gene expression and growth. A two-tier manifestation of cell-to-cell heterogeneity potentially occurs during the MazF-mediated stress response: first, the activation of the mazEF transcription is generally maintained at low levels, and the overall amount of MazF may be variable between single cells.…”

Structure, Biology, and Therapeutic Application of Toxin–Antitoxin Systems in Pathogenic Bacteria

“…Most of type I toxins are small hydrophobic peptides that disrupt bacterial membrane integrity and thereby cause defects in membrane potential and cell division. They are predicted to have a conserved α-helical transmembrane domain for pore formation, but their cellular functions and action mechanisms are highly diverse [74,75,77]. It remains to be investigated whether the pore formation provokes a detergent-like effect, as is found in many antibacterial peptides [78].…”

“…Toxic peptides can be extracellularly secreted and then lyse human host erythrocytes and competing bacteria with different strengths [89]. Recently, a regulatory crosstalk between the type I TA system ratA-txpA and its adjacent type II TA system mazEF was discovered in the human pathogen Enterococcus faecalis [77]. The MazEF complex can not only function as an autorepressors but also increase transcription levels of antitoxin-encoding ratA by using different promoters.…”

Linking bacterial type I toxins with their actions

“…Finally, TA systems should be considered as tiny modules embedded in larger regulatory networks where all of the different players interact. Indeed, recent discoveries implying crosstalk between type I and II TAs [50] suggest that numerous interactions involving different TA systems are yet to be discovered.…”