Choi Eunsil, Ryu Eunwoo, Kim Donghwee, Byun Ji-Won, Kim Kahyun, Lee Minho, Hwang Jihwan
Department of Microbiology, Pusan National University, Busan, Republic of Korea.
Microbiological Resource Research Institute, Pusan National University, Busan, Republic of Korea.
PLoS Pathog. 2025 Apr 9;21(4):e1013047. doi: 10.1371/journal.ppat.1013047. eCollection 2025 Apr.
The bactericidal/permeability-increasing protein (BPI)-inducible protein A (BipA) is a highly conserved protein in Gram-negative bacteria that is structurally similar to translational GTPases such as IF2, EF-Tu, and EF-G. Our previous research showed that deleting bipA in Escherichia coli at 20°C leads to a defect in 50S ribosomal assembly and impaired lipopolysaccharide (LPS) synthesis. This LPS defect activates the Regulator of Capsule Synthesis (Rcs) pathway, resulting in an overproduction of capsular polysaccharides, a reduction in biofilm formation, and decreased flagella-mediated motility. In this study, we aimed to elucidate the role of BipA in the pathogenicity of Salmonella enterica serovar Typhimurium. We constructed bipA deletion mutants in two pathogenic S. Typhimurium strains, SL1344 and 14028, as well as in the attenuated strain LT2. Our ribosome profiling experiments using the mutant S. Typhimurium strains revealed a defect in ribosome assembly at 20°C, with the accumulation of abnormal 50S ribosomal subunits. We further demonstrated that the absence of BipA in S. Typhimurium impaired LPS biosynthesis at 20°C, compromising membrane integrity and presumably activating the Rcs pathway. This activation altered virulence factors, including reduced biofilm formation, particularly in the 14028ΔbipA strain. Furthermore, the SL1344ΔbipA and 14028ΔbipA strains exhibited significantly decreased swimming motility at 20°C compared to 37°C, confirmed by microscopic observation showing fewer flagella at 20°C. Subsequently, both strains exhibited a significant reduction in invasion capability and cytotoxicity toward human intestinal epithelial cells (HCT116). This functional attenuation was corroborated by the decrease in virulence observed in the 14028ΔbipA strain in a mouse model. Our findings suggest that, in S. Typhimurium, BipA functions as a bacterial fitness factor, contributing to ribosome assembly, LPS synthesis, and virulence-related processes, particularly under stress conditions relevant to host environments.
杀菌/通透性增加蛋白（BPI）诱导蛋白A（BipA）是革兰氏阴性菌中一种高度保守的蛋白，其结构与翻译GTP酶如IF2、EF - Tu和EF - G相似。我们之前的研究表明，在20°C条件下删除大肠杆菌中的bipA会导致50S核糖体组装缺陷以及脂多糖（LPS）合成受损。这种LPS缺陷激活了荚膜合成调节因子（Rcs）途径，导致荚膜多糖过度产生、生物膜形成减少以及鞭毛介导的运动性降低。在本研究中，我们旨在阐明BipA在鼠伤寒沙门氏菌致病性中的作用。我们在两种致病性鼠伤寒沙门氏菌菌株SL1344和14028以及减毒株LT2中构建了bipA缺失突变体。我们使用突变的鼠伤寒沙门氏菌菌株进行的核糖体分析实验显示，在20°C时核糖体组装存在缺陷，异常的50S核糖体亚基积累。我们进一步证明，在20°C时鼠伤寒沙门氏菌中缺乏BipA会损害LPS生物合成，损害膜完整性并可能激活Rcs途径。这种激活改变了毒力因子，包括生物膜形成减少，特别是在14028ΔbipA菌株中。此外，与37°C相比，SL1344ΔbipA和14028ΔbipA菌株在20°C时的游动运动性显著降低，显微镜观察证实20°C时鞭毛数量减少。随后，两种菌株对人肠上皮细胞（HCT116）的侵袭能力和细胞毒性均显著降低。在小鼠模型中14028ΔbipA菌株中观察到的毒力降低证实了这种功能减弱。我们的研究结果表明，在鼠伤寒沙门氏菌中，BipA作为一种细菌适应性因子，有助于核糖体组装、LPS合成以及与毒力相关的过程，特别是在与宿主环境相关的应激条件下。
