The mitochondrial thiamine pyrophosphate transporter TptA promotes adaptation to low iron conditions and virulence in fungal pathogen <i>Aspergillus fumigatus</i>

<i>Aspergillus fumigatus</i> is the most prevalent airborne fungal pathogen that causes invasive fungal infections in immunosuppressed individuals. Adaptation to iron limited conditions is crucial for <i>A. fumigatus</i> virulence. To identify novel genes that play roles in adaptation to low iron conditions we performed an insertional mutagenesis screen in <i>A. fumigatus</i>. Using this approach, we identified the <i>tptA</i> gene in <i>A. fumigatus</i>, which shares homology with the <i>Saccharomyces cerevisiae</i> thiamine pyrophosphate (ThPP) transporter encoding gene <i>tpc1</i>. Heterologous expression of <i>tpc1</i> in the <i>tptA</i> deletion mutant completely restored the ThPP auxotrophy phenotype, suggesting that Tpc1 and TptA are functional orthologues. Importantly, TptA was required for adaptation to low iron conditions in <i>A. fumigatus</i>. The <i>ΔtptA</i> mutant had decreased resistance to the iron chelator bathophenanthroline disulfonate (BPS) with severe growth defects. Moreover, loss of <i>tptA</i> decreased the expression of <i>hapX</i>, which is a major transcription factor indispensable for adaptation to iron starvation in <i>A. fumigatus</i>. Overexpression of <i>hapX</i> in the <i>ΔtptA</i> strain greatly rescued the growth defect and siderophore production by <i>A. fumigatus</i> in iron-depleted conditions. Mutagenesis experiments demonstrated that the conserved residues related to ThPP uptake in TptA were also required for low iron adaptation. Furthermore, TptA-mediated adaptation to low iron conditions was found to be dependent on carbon sources. Finally, loss of <i>tptA</i> resulted in the attenuation of virulence in a murine model of aspergillosis. Taken together, this study demonstrated that the mitochondrial ThPP transporter TptA promotes low iron adaptation and virulence in <i>A. fumigatus</i>.烟曲霉（Aspergillus fumigatus）是最常见的空气传播真菌病原体，可引发免疫功能低下个体的侵袭性真菌感染。适应缺铁环境对烟曲霉的致病力至关重要。为鉴定参与缺铁环境适应的新基因，我们在烟曲霉中开展了插入诱变筛选实验。通过该策略，我们在烟曲霉中鉴定到tptA基因，该基因与酿酒酵母（Saccharomyces cerevisiae）编码焦磷酸硫胺素（ThPP）转运蛋白的tpc1基因具有同源性。在tptA缺失突变体中异源表达tpc1，可完全恢复其焦磷酸硫胺素营养缺陷型表型，表明Tpc1与TptA为功能同源物。重要的是，TptA是烟曲霉适应缺铁环境所必需的。ΔtptA突变体对铁螯合剂浴铜灵二磺酸盐（BPS）的抗性降低，并表现出严重的生长缺陷。此外，tptA的缺失会降低hapX的表达，而hapX是烟曲霉适应铁饥饿所必需的核心转录因子。在ΔtptA菌株中过表达hapX，可显著恢复烟曲霉在缺铁条件下的生长缺陷及铁载体产生能力。诱变实验证实，TptA中与焦磷酸硫胺素摄取相关的保守残基，同样是其适应缺铁环境所必需的。此外，研究发现TptA介导的缺铁环境适应依赖于碳源。最后，tptA的缺失会减弱烟曲霉在小鼠曲霉病模型中的致病力。综上，本研究证实，线粒体焦磷酸硫胺素转运蛋白TptA可促进烟曲霉的缺铁环境适应与致病力。