Abstract：
Enterococcus faecalis is a phylogenetically and industrially relevant microorganism associated with Lactic Acid Bacteria. Some strains of this bacterium are employed as probiotics in commercial applications, while others serve as the principal component in starter cultures for artisanal regional cheese production. However, over the last decade, this species has emerged as an opportunistic multiresistant pathogen, raising concerns about its impact on human health. Recently, we identified multiple potassium transporter systems in E. faecalis, including the Ktr systems (KtrAB and KtrAD), Kup, KimA and Kdp complex (KdpFABC). Nevertheless, the physiological significance of these proteins remains not fully understood. In this study, we observed that the kup gene promoter region in the JH2-2 strain was modified due to the insertion of a complete copy of the IS6770 insertion sequence. Consequently, we investigated the influence of IS6770 on the expression of the kup gene. To achieve this, we conducted a mapping of the promoter region of this gene in the E. faecalis JH2-2 strain, employing fluorescence gene reporters. In addition, a transcriptional analysis of the kup gene was executed in a strain derived from E. faecalis V583 that lacks the IS30-related insertion element, facilitating the identification of the transcriptional start site. Next, the expression of the kup gene was evaluated via RT-qPCR under different pH stressful conditions. A strong upregulation of the kup gene was observed at an initial pH of 5.0 in the strain derived from E. faecalis V583. However, the activation of transcription was not observed in the E. faecalis JH2-2 strain due to the hindrance caused by the presence of IS6770. Besides that, our computational analysis of E. faecalis genomes elucidates a plausible association between transposition and the regulation of the kup gene. Remarkably, the ubiquitous presence of IS6770 throughout the phylogenetic tree implies its ancient existence within E. faecalis. Moreover, the recurrent co-occurrence of IS6770 with the kup gene, observed in 30 % of IS6770-positive strains, alludes to the potential involvement of this genomic arrangement in the adaptive strategies of E. faecalis across diverse niches.
摘要：
粪肠球菌是与乳酸菌相关的系统发育和工业相关的微生物。这种细菌的一些菌株在商业应用中用作益生菌，而其他人则是手工区域奶酪生产的发酵剂文化的主要组成部分。然而,在过去的十年里，该物种已成为机会性多重抗性病原体，引起人们对其对人类健康影响的担忧。最近,我们在粪肠球菌中发现了多个钾转运系统，包括KTR系统(KtrAB和KtrAD)，Kup,KimA和Kdp复合体(KdpFABC)。然而，这些蛋白质的生理意义仍未完全了解。在这项研究中,我们观察到JH2-2菌株中的kup基因启动子区由于IS6770插入序列的完整拷贝的插入而被修饰。因此,我们研究了IS6770对kup基因表达的影响。为了实现这一点，我们在粪肠球菌JH2-2菌株中对该基因的启动子区域进行了定位，采用荧光基因报告基因。此外,在缺乏IS30相关插入元件的粪肠球菌V583菌株中进行了kup基因的转录分析，促进转录起始位点的鉴定。接下来,通过RT-qPCR在不同pH应激条件下评估kup基因的表达。在源自粪肠球菌V583的菌株中,在5.0的初始pH下观察到kup基因的强烈上调。然而,由于IS6770的存在引起的阻碍,在粪肠球菌JH2-2菌株中未观察到转录激活。除此之外,我们对粪肠球菌基因组的计算分析阐明了转座与kup基因调控之间的合理关联.值得注意的是,IS6770在整个系统发育树中普遍存在，这意味着它在粪肠球菌中的古老存在。此外，IS6770与kup基因的反复出现，在30%的IS6770阳性菌株中观察到，暗示这种基因组排列可能参与粪肠球菌在不同生态位的适应性策略。
