Rees Christiaan A, Stefanuto Pierre-Hugues, Beattie Sarah R, Bultman Katherine M, Cramer Robert A, Hill Jane E
Geisel School of Medicine, Dartmouth College, Hanover, NH 03755, United States of America.
J Breath Res. 2017 Aug 21;11(3):036003. doi: 10.1088/1752-7163/aa7b3e.
Invasive aspergillosis (IA) is a life-threatening infectious disease caused by fungi from the genus Aspergillus, with an associated mortality as high as 90% in certain populations. IA-associated pulmonary lesions are characteristically depleted in oxygen relative to normal lung tissue, and it has been shown that the most common causal agent of IA, Aspergillus fumigatus, must respond to low-oxygen environments for pathogenesis and disease progression. Previous studies have demonstrated marked alterations to the Aspergillus fumigatus transcriptome in response to low-oxygen environments that induce a 'hypoxia response'. Consequently, we hypothesized that these transcriptomic changes would alter the volatile metabolome and generate a volatile hypoxia signature. In the present study, we analyzed the volatile molecules produced by A. fumigatus in both oxygen replete (normoxia) and depleted (hypoxia) environments via headspace solid-phase micro-extraction coupled to two-dimensional gas chromatography-time-of-flight mass spectrometry. Using the machine learning algorithm random forest, we identified 19 volatile molecules that were discriminatory between the four growth conditions assessed in this study (i.e., early hypoxia (1 h), late hypoxia (8 h), early normoxia (1 h), and late normoxia (8 h)), as well as a set of 19 that were discriminatory between late hypoxia cultures and all other growth conditions in aggregate. Nine molecules were common to both comparisons, while the remaining 20 were specific to only one of two. We assigned putative identifications to 13 molecules, of which six were most highly abundant in late hypoxia cultures. Previously acquired transcriptomic data identified putative biochemical pathways induced in hypoxia conditions that plausibly account for the production of a subset of these molecules, including 2,3-butanedione and 3-hydroxy-2-butanone. These two molecules may represent a novel hypoxia fitness pathway in A. fumigatus, and could be useful in the detection of hypoxia-associated A. fumigatus lesions that develop in established IA infections.
侵袭性曲霉病（IA）是一种由曲霉属真菌引起的危及生命的传染病，在某些人群中相关死亡率高达90%。与IA相关的肺部病变相对于正常肺组织而言，其特征是氧气含量降低，并且已经表明，IA最常见的病原体烟曲霉在致病和疾病进展过程中必须对低氧环境作出反应。先前的研究表明，烟曲霉转录组在低氧环境下会发生显著变化，从而引发“缺氧反应”。因此，我们推测这些转录组变化会改变挥发性代谢组，并产生挥发性缺氧特征。在本研究中，我们通过顶空固相微萃取结合二维气相色谱 - 飞行时间质谱分析了烟曲霉在富氧（常氧）和贫氧（缺氧）环境中产生的挥发性分子。使用机器学习算法随机森林，我们鉴定出19种挥发性分子在本研究评估的四种生长条件（即早期缺氧（1小时）、晚期缺氧（8小时）、早期常氧（1小时）和晚期常氧（8小时））之间具有区分性，以及一组19种在晚期缺氧培养物与所有其他生长条件总体之间具有区分性。在这两个比较中，有9种分子是共同的，而其余20种仅特定于其中之一。我们对13种分子进行了推定鉴定，其中6种在晚期缺氧培养物中含量最高。先前获得的转录组数据确定了在缺氧条件下诱导的推定生化途径，这些途径可能解释了这些分子中一部分的产生，包括2,3 - 丁二酮和3 - 羟基 - 2 - 丁酮。这两种分子可能代表烟曲霉中的一种新型缺氧适应途径，并且可用于检测在已建立的IA感染中发生的与缺氧相关的烟曲霉病变。
