Department of Microbiology, Chungnam National University School of Medicine, Daejeon, 35015, Republic of Korea.
Department of Medical Science, Chungnam National University, Daejeon, 34134, Republic of Korea.
J Microbiol. 2020 Jun;58(6):519-529. doi: 10.1007/s12275-020-0186-1. Epub 2020 May 27.
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.
适应不断变化的环境条件对微生物的生存至关重要。细菌已经进化出各种机制来应对渗透胁迫。在这里，我们报告了在医院不动杆菌中鉴定和功能表征渗透胁迫反应操纵子 betIBA 的情况。betIBA 操纵子编码的酶对于胆碱转化为渗透压保护剂甘氨酸甜菜碱非常重要。betIBA 操纵子是多顺反子的，并且受到相同操纵子的第一个基因 betI 的调控。生物信息学分析显示 betIBA 操纵子上游存在 BetI 结合基序，电泳迁移率变动分析证实了 BetI 的特异性结合。mRNA 表达分析显示，与野生型相比，betI、betB 和 betA 基因在 betI 缺失突变体中的表达升高，证实了自阻遏物 BetI 在医院不动杆菌中抑制 betIBA 操纵子。我们进一步发现 betIBA 操纵子受群体感应（QS）调节剂 AnoR 的转录调控，在医院不动杆菌中。随后分析 BetI 对 QS 基因 anoR 和 anoI 表达的影响表明，BetI 作为 anoR 和 anoI 的抑制剂。此外，注意到渗透压应激反应调节剂 OmpR 可能在控制医院不动杆菌 betIBA 操纵子的表达中发挥重要作用。总之，这些数据表明，QS 和渗透压应激反应系统在医院不动杆菌中相关联，并且两个系统中的基因表达都通过各种反馈环根据渗透压条件进行精细调节。
