施氏假单胞菌A1501铁吸收调节蛋白Fur的表达特性与功能鉴定

铁是细胞生理代谢的重要金属元素，是多种氧化还原酶类、过氧化物酶类的重要组成部分。革兰氏阴性菌中，胞内铁转运、储存和利用主要由铁吸收调节蛋白Fur（ferric uptake regulator）调控。水稻根际联合固氮菌——施氏假单胞菌（Pseudomonas stutzeri）A1501基因组中含有一个fur同源基因，但其具体功能尚不清楚。比较了A1501中fur基因及其编码蛋白的序列特征，并通过实时荧光定量PCR（real-time quantitative，qRT-PCR）和Western blotting杂交方法测定了fur基因和Fur蛋白的表达特性，结果发现fur基因表达水平与环境中铁浓度呈负相关，在铁限制条件下高表达，铁过量条件下表达受抑制。构建了fur基因突变株和功能回补株，表型测定发现fur突变影响了A1501的碳源代谢谱，并导致A1501对过氧化氢胁迫敏感。胞内铁含量测定表明，fur突变株内的铁含量为野生型的1.3倍，进一步qRT-PCR测定表明fur突变影响了铁离子转运系统及过氧化物酶编码基因的表达。研究结果为解析根际微生物胞内铁平衡调节及根际环境适应机制奠定了理论基础。

Expressional and Functional Characterization of the Ferric Uptake Regulator Fur in Pseudomonas stutzeri A1501

Iron is one of the inevitable metal elements for cell physiological metabolisms， and an important co-factor for a variety of oxidoreductases and peroxidases. In Gram-negative bacteria， the intracellular iron transport， storage and utilization are mainly regulated by the ferric uptake regulator （Fur）. A fur homologous gene was identified in the genome of Pseudomonas stutzeri A1501 which is a root-associated nitrogen-fixing bacterium， but its function was still unclear. In this study， the biological information， especially the sequence difference of both the fur genes and the Fur proteins among A1501 and other typical bacteria were compared. The expression characteristics of the fur gene and the Fur protein in A1501 were explored via the application of both real-time quantitative PCR （qRT-PCR） and Western blotting. The results showed that both the Fur protein and the fur gene were highly expressed under iron-limited conditions but the expression inhibited under iron-exceed conditions. The fur knockout mutant and functional complementary strains were constructed. It was observed that deletion of fur affected the carbon source metabolic spectrum of A1501 and also caused higher sensitivity to hydrogen peroxide stress. Meanwhile， the level of intracellular iron in the fur mutant was 1.3 times of that in wild type. Further qRT-PCR analysis indicated that Fur regulated the expression of the intracellular iron transport system and superoxide dismutase genes. This study provided a theoretical basis for the analysis of the intracellular iron homeostatic regulation and rhizosphere environment adaptation of rhizosphere microorganisms.