Liao Chun-Hsing, Lu Hsu-Feng, Huang Hsin-Hui, Chen Yu, Li Li-Hua, Lin Yi-Tsung, Yang Tsuey-Ching
Division of Infectious Disease, Far Eastern Memorial Hospital, New Taipei City, Taiwan.
Department of Medicine, National Yang Ming Chiao Tung University, Taipei, Taiwan.
J Biomed Sci. 2022 Apr 27;29(1):26. doi: 10.1186/s12929-022-00809-y.
Stenotrophomonas maltophilia, a member of γ-proteobacteria, is a ubiquitous environmental bacterium that is recognized as an opportunistic nosocomial pathogen. FecABCD system contributes to ferric citrate acquisition in Escherichia coli. FeoABC system, consisting of an inner membrane transporter (FeoB) and two cytoplasmic proteins (FeoA and FeoC), is a well-known ferrous iron transporter system in γ-proteobacteria. As revealed by the sequenced genome, S. maltophilia appears to be equipped with several iron acquisition systems; however, the understanding of these systems is limited. In this study, we aimed to elucidate the ferric citrate acquisition system of S. maltophilia.
Candidate genes searching and function validation are the strategy for elucidating the genes involved in ferric citrate acquisition. The candidate genes responsible for ferric citrate acquisition were firstly selected using FecABCD of E. coli as a reference, and then revealed by transcriptome analysis of S. maltophilia KJ with and without 2,2'-dipyridyl (DIP) treatment. Function validation was carried out by deletion mutant construction and ferric citrate utilization assay. The bacterial adenylate cyclase two-hybrid system was used to verify intra-membrane protein-protein interaction.
Smlt2858 and Smlt2356, the homologues of FecA and FecC/D of E. coli, were first considered; however, deletion mutant construction and functional validation ruled out their involvement in ferric citrate acquisition. FciA (Smlt1148), revealed by its upregulation in DIP-treated KJ cells, was the outer membrane receptor for ferric citrate uptake. The fciA gene is a member of the fciTABC operon, in which fciT, fciA, and fciC participated in ferric citrate acquisition. Uniquely, the Feo system of S. maltophilia is composed of a cytoplasmic protein FeoA, an inner membrane transporter FeoB, and a predicted inner membrane protein FeoI. The intra-membrane protein-protein interaction between FeoB and FeoI may extend the substrate profile of FeoB to ferric citrate. FeoABI system functioned as an inner membrane transporter of ferric citrate.
The FciTABC and FeoABI systems contribute to ferric citrate acquisition in S. maltophilia.
嗜麦芽窄食单胞菌是γ-变形菌纲的成员，是一种普遍存在于环境中的细菌，被认为是一种机会性医院病原体。FecABCD系统有助于大肠杆菌摄取柠檬酸铁。FeoABC系统由内膜转运蛋白（FeoB）和两种胞质蛋白（FeoA和FeoC）组成，是γ-变形菌纲中一种著名的亚铁转运系统。测序基因组显示，嗜麦芽窄食单胞菌似乎具备多种铁摄取系统；然而，对这些系统的了解有限。在本研究中，我们旨在阐明嗜麦芽窄食单胞菌的柠檬酸铁摄取系统。
通过搜索候选基因和功能验证来阐明参与柠檬酸铁摄取的基因。首先以大肠杆菌的FecABCD为参考选择负责摄取柠檬酸铁的候选基因，然后通过对经2,2'-联吡啶（DIP）处理和未处理的嗜麦芽窄食单胞菌KJ进行转录组分析来揭示这些基因。通过构建缺失突变体和柠檬酸铁利用试验进行功能验证。使用细菌腺苷酸环化酶双杂交系统验证膜内蛋白质-蛋白质相互作用。
最初考虑了大肠杆菌FecA和FecC/D的同源物Smlt2858和Smlt2356；然而，构建缺失突变体和功能验证排除了它们参与柠檬酸铁摄取的可能性。FciA（Smlt1148）在经DIP处理的KJ细胞中上调，是摄取柠檬酸铁的外膜受体。fciA基因是fciTABC操纵子的成员，其中fciT、fciA和fciC参与柠檬酸铁摄取。独特的是，嗜麦芽窄食单胞菌的Feo系统由胞质蛋白FeoA、内膜转运蛋白FeoB和预测的内膜蛋白FeoI组成。FeoB和FeoI之间的膜内蛋白质-蛋白质相互作用可能将FeoB的底物谱扩展到柠檬酸铁。FeoABI系统作为柠檬酸铁的内膜转运蛋白发挥作用。
FciTABC和FeoABI系统有助于嗜麦芽窄食单胞菌摄取柠檬酸铁。
