Moritz Katharina D, Amendt Birgit, Witt Elisabeth M H J, Galinski Erwin A
Institut für Mikrobiologie und Biotechnologie, Rheinische Friedrich-Wilhelms-Universität Bonn, Meckenheimer Allee 168, 53115, Bonn, Germany,
Extremophiles. 2015 Jan;19(1):87-99. doi: 10.1007/s00792-014-0687-0. Epub 2014 Aug 21.
Acidiphilium cryptum is an acidophilic, heterotrophic α-Proteobacterium which thrives in acidic, metal-rich environments (e.g. acid mine drainage). Recently, an ectABCDask gene cluster for biosynthesis of the compatible solutes ectoine and hydroxyectoine was detected in the genome sequence of A. cryptum JF-5. We were able to demonstrate that the type strain A. cryptum DSM 2389(T) is capable of synthesizing the compatible solute hydroxyectoine in response to moderate osmotic stress caused by sodium chloride and aluminium sulphate, respectively. Furthermore, we used the A. cryptum JF-5 sequence to amplify the ectABCDask gene cluster from strain DSM 2389(T) and achieved heterologous expression of the gene cluster in Escherichia coli. Hence, we could for the first time prove metabolic functionality of the genes responsible for hydroxyectoine biosynthesis in the acidophile A. cryptum. In addition, we present information on specific enzyme activity of A. cryptum DSM 2389(T) ectoine synthase (EctC) in vitro. In contrast to EctCs from halophilic microorganisms, the A. cryptum enzyme exhibits a higher isoelectric point, thus a lower acidity, and has maximum specific activity in the absence of sodium chloride.
嗜酸隐秘杆菌是一种嗜酸、异养的α-变形菌，在酸性、富含金属的环境（如酸性矿山排水）中生长旺盛。最近，在嗜酸隐秘杆菌JF-5的基因组序列中检测到一个用于合成相容性溶质四氢嘧啶和羟基四氢嘧啶的ectABCDask基因簇。我们能够证明模式菌株嗜酸隐秘杆菌DSM 2389(T)能够分别响应由氯化钠和硫酸铝引起的中等渗透胁迫，合成相容性溶质羟基四氢嘧啶。此外，我们利用嗜酸隐秘杆菌JF-5的序列从菌株DSM 2389(T)中扩增出ectABCDask基因簇，并在大肠杆菌中实现了该基因簇的异源表达。因此，我们首次证明了嗜酸菌嗜酸隐秘杆菌中负责羟基四氢嘧啶生物合成的基因的代谢功能。此外，我们还提供了嗜酸隐秘杆菌DSM 2389(T)四氢嘧啶合酶（EctC）体外比酶活性的信息。与嗜盐微生物的EctC不同，嗜酸隐秘杆菌的这种酶具有更高的等电点，因此酸度更低，并且在没有氯化钠的情况下具有最大比活性。
