Adaptation to changing environmental conditions is crucial for the survival of microorganisms. Bacteria have evolved various mechanisms to cope with osmotic stress. Here, we report the identification and functional characterization of the osmotic stress response operon, betIBA, in Acinetobacter nosocomialis. The betIBA operon encodes enzymes that are important for the conversion of choline to the osmoprotectant, glycine betaine. The betIBA operon is polycistronic and is under the regulation of the first gene, betI, of the same operon. A bioinformatics analysis revealed the presence of a BetI-binding motif upstream of the betIBA operon, and electrophoretic mobility shift assays confirmed the specific binding of BetI. An mRNA expression analysis revealed that expression of betI, betB, and betA genes is elevated in a betI-eletion mutant compared with the wild type, confirming that the autorepressor BetI represses the betIBA operon in A. nosocomialis. We further found that the betIBA operon is under the transcriptional control of the quorum-sensing (QS) regulator, AnoR in, A. nosocomialis. A subsequent analysis of the impact of BetI on expression of the QS genes, anoR and anoI, demonstrated that BetI acts as a repressor of anoR and anoI. In addition, it was noticed that the osmotic stress response regulator, OmpR might play an important role in controlling the expression of betIBA operon in A. nosocomialis. Collectively, these data demonstrate that QS and osmotic stress-response systems are correlated in A. nosocomialis and that the expression of genes in both systems is finely tuned by various feedback loops depending on osmolarity conditions.

中文翻译：

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渗透应激反应操纵子 betIBA 受 BetI 和院内不动杆菌中群体感应调节因子 AnoR 的功能调节。

适应不断变化的环境条件对于微生物的生存至关重要。细菌已经进化出多种机制来应对渗透压。在这里，我们报告了院内不动杆菌中渗透应激反应操纵子betIBA的鉴定和功能表征。betIBA操纵子编码的酶对于将胆碱转化为渗透保护剂甘氨酸甜菜碱很重要。betIBA操纵子是多顺反子，并且受同一操纵子的第一个基因betI的调控。生物信息学分析揭示了betIBA上游存在 BetI 结合基序操纵子和电泳迁移率变动分析证实了 BetI 的特异性结合。mRNA 表达分析表明，与野生型相比，betI、betB和betA基因的表达在betI突变体中升高，证实了自阻遏物 BetI 抑制院内放线菌中的betIBA操纵子。我们进一步发现betIBA操纵子在A. nosocomialis中的群体感应 (QS) 调节器 AnoR 的转录控制下。随后分析 BetI 对 QS 基因、 anoR和anoI表达的影响, 表明 BetI 充当anoR和anoI的阻遏物。此外，人们注意到渗透压应激反应调节剂 OmpR 可能在控制院内放线菌中betIBA操纵子的表达方面发挥重要作用。总的来说，这些数据表明 QS 和渗透应激反应系统在院内放线菌中是相关的，并且两个系统中的基因表达根据渗透压条件通过各种反馈回路进行微调。