Shao ZhiHui, Deng WanXin, Li ShiYuan, He JuanMei, Ren ShuangXi, Huang WeiRen, Lu YinHua, Zhao GuoPing, Cai ZhiMing, Wang Jin
CAS Key Laboratory of Synthetic Biology, Institute of Plant Physiology and Ecology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
Key Laboratory of Medical Reprogramming Technology, Shenzhen Second People's Hospital, First Affiliated Hospital of Shenzhen University, Shenzhen, China.
J Bacteriol. 2015 Oct;197(19):3041-7. doi: 10.1128/JB.00185-15. Epub 2015 Jul 13.
Ectoine and hydroxyectoine are excellent compatible solutes for bacteria to deal with environmental osmotic stress and temperature damages. The biosynthesis cluster of ectoine and hydroxyectoine is widespread among microorganisms, and its expression is activated by high salinity and temperature changes. So far, little is known about the mechanism of the regulation of the transcription of ect genes and only two MarR family regulators (EctR1 in methylobacteria and the EctR1-related regulator CosR in Vibrio cholerae) have been found to negatively regulate the expression of ect genes. Here, we characterize GlnR, the global regulator for nitrogen metabolism in actinomycetes, as a negative regulator for the transcription of ectoine/hydroxyectoine biosynthetic genes (ect operon) in Streptomyces coelicolor. The physiological role of this transcriptional repression by GlnR is proposed to protect the intracellular glutamate pool, which acts as a key nitrogen donor for both the nitrogen metabolism and the ectoine/hydroxyectoine biosynthesis.
High salinity is deleterious, and cells must evolve sophisticated mechanisms to cope with this osmotic stress. Although production of ectoine and hydroxyectoine is one of the most frequently adopted strategies, the in-depth mechanism of regulation of their biosynthesis is less understood. So far, only two MarR family negative regulators, EctR1 and CosR, have been identified in methylobacteria and Vibrio, respectively. Here, our work demonstrates that GlnR, the global regulator for nitrogen metabolism, is a negative transcriptional regulator for ect genes in Streptomyces coelicolor. Moreover, a close relationship is found between nitrogen metabolism and osmotic resistance, and GlnR-mediated regulation of ect transcription is proposed to protect the intracellular glutamate pool. Meanwhile, the work reveals the multiple roles of GlnR in bacterial physiology.
四氢嘧啶和羟基四氢嘧啶是细菌应对环境渗透压胁迫和温度损伤的优良相容性溶质。四氢嘧啶和羟基四氢嘧啶的生物合成簇在微生物中广泛存在，其表达受高盐度和温度变化激活。到目前为止，关于ect基因转录调控机制知之甚少，仅发现两个MarR家族调节因子（甲基杆菌中的EctR1和霍乱弧菌中与EctR1相关的调节因子CosR）对ect基因的表达起负调控作用。在此，我们鉴定出放线菌氮代谢全局调节因子GlnR是天蓝色链霉菌中四氢嘧啶/羟基四氢嘧啶生物合成基因（ect操纵子）转录的负调节因子。GlnR这种转录抑制的生理作用被认为是保护细胞内谷氨酸池，谷氨酸池是氮代谢和四氢嘧啶/羟基四氢嘧啶生物合成的关键氮供体。
高盐度是有害的，细胞必须进化出复杂的机制来应对这种渗透压胁迫。尽管产生四氢嘧啶和羟基四氢嘧啶是最常用的策略之一，但其生物合成的深入调控机制尚不清楚。到目前为止，仅在甲基杆菌和弧菌中分别鉴定出两个MarR家族负调节因子EctR1和CosR。在此，我们的工作表明，氮代谢全局调节因子GlnR是天蓝色链霉菌中ect基因的负转录调节因子。此外，发现氮代谢与渗透压抗性之间存在密切关系，并且认为GlnR介导的ect转录调控可保护细胞内谷氨酸池。同时，这项工作揭示了GlnR在细菌生理学中的多种作用。
