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

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.我们在临床分离株粪肠球菌（E. faecalis）V583中发现了一个包含两个毒素-抗毒素模块（TAs）的染色体位点，二者呈反义转录排布。这两个模块分别同源于I型txpA-ratA系统与II型mazEF系统。我们已证实，推定的MazF对大肠杆菌（E. coli）具有毒性，并可引发RNA降解，其同源抗毒素MazE可抵消该毒性。毗邻mazEF的第二个模块所表达的毒素被归类为厚壁菌门中存在的TxpA I型家族成员，其抗毒素则为反义RNA RatA。基因组分析表明，mazEF与txpA-ratA模块的顺式关联在进化过程中受到正向选择，提示该TA排布模式在粪肠球菌物种中具有选择优势。我们证实了两个模块间存在涉及转录调控与RNA稳定性的调控互作。值得注意的是，我们的数据揭示MazE与MazEF具有双重转录活性：它们既是自主阻遏因子，又可直接激活ratA的转录（极有可能为直接作用）。RatA通过调控稳定性控制txpA的RNA水平。我们的研究结果表明，MazEF在粪肠球菌V583中mazEF与txpA-ratA模块的协同表达中发挥关键作用。据我们所知，这是首次报道I型与II型TA之间存在交叉对话的研究。