大豆斑疹病菌铁摄取因子PiuB在致病性中的作用分析

The role of iron-uptake factor PiuB in pathogenicity of soybean pathogen Xanthomonas axonopodis pv.glycines

摘要:

铁作为生命必需的基本元素，在细菌生长代谢过程中具有重要作用。然而，大豆斑疹病菌(Xanthomonas axonopodis pv. glycines, Xag)中编码铁摄取因子的piuB基因是否参与病原菌的铁摄取和致病性并不清楚。为解析PiuB的作用，采用同源重组策略获得了Xag的piuB基因缺失突变株(ΔpiuB)，并对该突变株进行功能研究。研究表明：相较于野生型，突变株ΔpiuB在寄主大豆上的毒性和生长能力显著削弱；铁载体分泌量激增；对Fe³⁺、Cu²⁺、Zn²⁺和Mn²⁺的敏感性显著增强。此外，该突变株的H₂O₂抗性、胞外多糖产量、生物膜形成能力以及游动性等相较于野生型均显著减弱；添加外源Fe³⁺不能有效恢复ΔpiuB的上述特性；功能互补株可完全恢复ΔpiuB的缺陷性表型至野生型水平。这说明PiuB是Xag摄取Fe³⁺的潜在因子，并且是Xag在寄主大豆上致病所需的。

Abstract:

Iron is an essential element for living organisms that plays critical roles in the process of bacterial growth and metabolism. However, it remains to be elucidated whether piuB encoding iron-uptake factor is involved in iron uptake and pathogenicity of Xanthomonas axonopodis pv. glycines (Xag). To investigate the function of piuB, we firstly generated a piuB deletion mutant (ΔpiuB) by homologous recombination. Compared with the wild-type, the piuB mutant exhibited significantly reduced growth and virulence in host soybean. The mutant displayed markedly increased siderophore secretory volume, and its sensitivity to Fe³⁺, Cu²⁺, Zn²⁺ and Mn²⁺ was significantly enhanced. Additionally, the H₂O₂ resistance, exopolysaccharide yield, biofilm formation, and cell mobility of ΔpiuB were significantly diminished compared to that of the wild-type. The addition of exogenous Fe³⁺ cannot effectively restore the above characteristics of ΔpiuB. However, expressing piuB in trans rescued the properties lost by ΔpiuB to the levels in the wild-type. Taken together, our results demonstrated that PiuB is a potential factor for Xag to assimilate Fe³⁺, and is necessary for Xag to be pathogenic in host soybean.