Department of Pathology and Laboratory Medicine, Shin Kong Wu Ho-Su Memorial Hospital, Taipei, Taiwan.
School of Medical Laboratory Science and Biotechnology, Taipei Medical University, Taipei, Taiwan.
Microbiol Spectr. 2022 Jun 29;10(3):e0032122. doi: 10.1128/spectrum.00321-22. Epub 2022 Jun 6.
The hemin acquisition system of Stenotrophomonas maltophilia was elucidated in this study. To identify the TonB-dependent outer membrane receptor for hemin in S. maltophilia, the hemin acquisition systems of Pseudomonas aeruginosa were referenced. PhuR, HasA, and HxuA are three known TonB-dependent outer membrane receptors involved in hemin acquisition by P. aeruginosa. Thus, HemA (Smlt0795) and Smlt2937, the orthologs of PhuR and HasA/HxuA in S. maltophilia, were first considered. KJΔEnt, a stenobactin-null strain, was used as the parental strain for the hemin utilization assay. Deletion of , but not Smlt2937, of KJΔEnt impaired hemin acquisition under iron-depleted conditions, indicating that HemA is the TonB-dependent receptor for hemin uptake. The gene is a member of the operon, whose expression was upregulated in a mutant and under iron-depleted conditions. The contribution of the operon to hemin acquisition was investigated by in-frame deletion mutant construction and hemin utilization assays. Inactivation of , , and of KJΔEnt insignificantly affected hemin acquisition under iron-depleted conditions. However, deletion in a mutant increased hemin acquisition under iron-depleted conditions. Collectively, we revealed that (i) HemA likely functions as the outer membrane receptor for hemin uptake; (ii) HemP, a predicted transcriptional factor, apparently functions as a repressor of the expression of the transcript; and (iii) in a mutant, HemP has a negative impact on hemin acquisition under iron-depleted conditions. Stenotrophomonas maltophilia is an emerging multidrug-resistant opportunistic pathogen, increasing the difficulty of treatment of this infection. Iron is a critical element for bacterial viability. Heme is the most abundant iron source in the human host; thus, heme is the major iron source for a pathogen in the infection niche. Blocking iron acquisition from heme can be an alternative strategy to control S. maltophilia infection. Although several hemin acquisition systems have been reported in various pathogens, very little is known about the hemin acquisition systems of S. maltophilia. By in-frame deletion mutant construction and hemin utilization assays, we demonstrated that HemA (Smlt0795) is the TonB-dependent outer membrane receptor for hemin uptake and that HemP (Smlt0794), a predicted transcriptional factor, had a negative impact on hemin acquisition in a mutant. The negative regulatory role of HemP in hemin acquisition is first reported.
本研究阐明了嗜麦芽寡养单胞菌的血红素获取系统。为了鉴定嗜麦芽寡养单胞菌中血红素的 TonB 依赖性外膜受体，参考了铜绿假单胞菌的血红素获取系统。PhuR、HasA 和 HxuA 是三种已知的参与铜绿假单胞菌血红素获取的 TonB 依赖性外膜受体。因此，首先考虑了嗜麦芽寡养单胞菌中的 HemA（Smlt0795）和 Smlt2937，它们是 PhuR 和 HasA/HxuA 的同源物。KJΔEnt（一种 Stenobactin 缺失株）被用作血红素利用测定的亲本菌株。KJΔEnt 的 缺失，但不是 Smlt2937 的缺失，在缺铁条件下损害了血红素的获取，表明 HemA 是血红素摄取的 TonB 依赖性受体。 基因是 操纵子的成员，其表达在 突变体和缺铁条件下上调。通过框内缺失突变体构建和血红素利用测定研究了 操纵子对血红素获取的贡献。在 KJΔEnt 中失活 、 、 和 对缺铁条件下的血红素获取没有显著影响。然而，在 突变体中 缺失增加了缺铁条件下的血红素获取。总的来说，我们揭示了：（i）HemA 可能作为血红素摄取的外膜受体发挥作用；（ii）HemP，一种预测的转录因子，显然作为 转录物表达的阻遏物发挥作用；和（iii）在 突变体中，HemP 对缺铁条件下的血红素获取有负面影响。嗜麦芽寡养单胞菌是一种新兴的多药耐药机会性病原体，增加了这种感染治疗的难度。铁是细菌生存的关键元素。血红素是宿主中最丰富的铁源；因此，血红素是感染部位病原体的主要铁源。阻断血红素从铁中的获取可以是控制嗜麦芽寡养单胞菌感染的一种替代策略。尽管已经在各种病原体中报道了几种血红素获取系统，但对嗜麦芽寡养单胞菌的血红素获取系统知之甚少。通过框内缺失突变体构建和血红素利用测定，我们证明了 HemA（Smlt0795）是血红素摄取的 TonB 依赖性外膜受体，预测的转录因子 HemP（Smlt0794）在 突变体中对血红素获取有负面影响。HemP 在血红素获取中的负调控作用是首次报道的。
