Miethke Marcus, Schmidt Sarah, Marahiel Mohamed A
Fachbereich Chemie/Biochemie der Philipps-Universität Marburg, Hans Meerwein Strasse, D-35032 Marburg, Germany.
J Bacteriol. 2008 Aug;190(15):5143-52. doi: 10.1128/JB.00464-08. Epub 2008 May 23.
High-affinity iron acquisition in Bacillus subtilis is mediated via the bacillibactin catechole siderophore pathway. Three of the four essential pathway steps, bacillibactin synthesis, Fe-bacillibactin uptake, and Fe-bacillibactin hydrolysis have been characterized previously. The functional and regulatory components for bacillibactin secretion, the second step of the siderophore pathway, remained unknown. In this study, the screening of a B. subtilis exporter mutant library led to the identification of the YmfE major facilitator superfamily (MFS)-type transporter as a target for bacillibactin export. Analysis of iron-limited ymfE mutant cultures displayed an eightfold reduced bacillibactin secretion and, on the other hand, a 25-fold increased secretion of the bacillibactin precursor 2,3-dihydroxybenzoate. Investigation of the regulatory aspect revealed that bacillibactin secretion is, in contrast to all other components of the pathway, independent of the ferric uptake repressor Fur. Indeed, the MerR-type transcriptional regulator Mta was found to activate both bacillibactin secretion and ymfE gene expression, exposing Mta as an additional regulatory member of the bacillibactin pathway.
枯草芽孢杆菌中的高亲和力铁摄取是通过杆菌铁载体儿茶酚途径介导的。四个基本途径步骤中的三个，即杆菌铁载体合成、铁-杆菌铁载体摄取和铁-杆菌铁载体水解，此前已得到表征。铁载体途径第二步，即杆菌铁载体分泌的功能和调控成分仍不清楚。在本研究中，对枯草芽孢杆菌外排突变体文库的筛选导致鉴定出YmfE主要易化子超家族（MFS）型转运蛋白作为杆菌铁载体外排的靶点。对铁限制的ymfE突变体培养物的分析显示，杆菌铁载体分泌减少了八倍，另一方面，杆菌铁载体前体2,3-二羟基苯甲酸的分泌增加了25倍。对调控方面的研究表明，与该途径的所有其他成分不同，杆菌铁载体分泌不依赖于铁摄取阻遏物Fur。事实上，发现MerR型转录调节因子Mta可激活杆菌铁载体分泌和ymfE基因表达，表明Mta是杆菌铁载体途径的另一个调控成员。
