Feeding on compatible solutes: A substrate‐induced pathway for uptake and catabolism of ectoines and its genetic control by EnuR
Feeding on compatible solutes: A substrate‐induced pathway for uptake and catabolism of ectoines and its genetic control by EnuR
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DOI：
10.1111/1462-2920.13414
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发表时间：
2017-03
影响因子：
5.1
通讯作者：
J. E. Hallsworth;A. Schulz;Nadine Stöveken;Ina Binzen;T. Hoffmann;J. Heider;E. Bremer
中科院分区：
文献类型：
--
作者：
J. E. Hallsworth;A. Schulz;Nadine Stöveken;Ina Binzen;T. Hoffmann;J. Heider;E. Bremer
外托因和5-羟基外托因是广泛合成的微生物渗透胁迫保护剂。它们也是多用途营养素，但其分解代谢和相应基因的遗传调控尚不完全清楚。利用海洋细菌Ruegeria pomeroyi DSS-3，我们研究了异托因的利用，并提出了一个七个步骤，包括5-羟基异托因转化为异托因，打开异托因环，随后将该中间体降解为l-天冬氨酸的分解代谢途径。分解代谢基因与3个编码5-羟基异托因/异托因特异性TRAP转运体的基因共转录。整个基因簇的染色体缺失取消了利用外托因作为碳和氮源。生长培养基中外托因的存在触发了进口和分解代谢操纵子的增强表达，这一过程依赖于该基因簇之前的底物诱导启动子。EnuR是MocR/ gabr型转录调控因子的一员，控制该启动子的活性并发挥抑制因子的作用。EnuR含有一个共价结合的吡哆醛-5'-磷酸，我们认为这个辅助因子对于底物介导的5-羟基外托因/外托因进口和分解代谢基因的诱导至关重要。生物信息学表明，外托因的消费者仅限于变形菌门，EnuR可能是大多数外托因/5-羟基外托因分解代谢基因的中心调节因子。
Ectoine and 5-hydroxyectoine are widely synthesized microbial osmostress protectants. They are also versatile nutrients but their catabolism and the genetic regulation of the corresponding genes are incompletely understood. Using the marine bacterium Ruegeria pomeroyi DSS-3, we investigated the utilization of ectoines and propose a seven steps comprising catabolic route that entails an initial conversion of 5-hydroxyectoine to ectoine, the opening of the ectoine ring, and the subsequent degradation of this intermediate to l-aspartate. The catabolic genes are co-transcribed with three genes encoding a 5-hydroxyectoine/ectoine-specific TRAP transporter. A chromosomal deletion of this entire gene cluster abolishes the utilization of ectoines as carbon and nitrogen sources. The presence of ectoines in the growth medium triggers enhanced expression of the importer and catabolic operon, a process dependent on a substrate-inducible promoter that precedes this gene cluster. EnuR, a member of the MocR/GabR-type transcriptional regulators, controls the activity of this promoter and functions as a repressor. EnuR contains a covalently bound pyridoxal-5'-phosphate, and we suggest that this co-factor is critical for the substrate-mediated induction of the 5-hydroxyectoine/ectoine import and catabolic genes. Bioinformatics showed that ectoine consumers are restricted to the Proteobacteria and that EnuR is likely a central regulator for most ectoine/5-hydroxyectoine catabolic genes.