Schroeckh Volker, Scherlach Kirstin, Nützmann Hans-Wilhelm, Shelest Ekaterina, Schmidt-Heck Wolfgang, Schuemann Julia, Martin Karin, Hertweck Christian, Brakhage Axel A
Department of Molecular and Applied Microbiology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute, 07745 Jena, Germany.
Proc Natl Acad Sci U S A. 2009 Aug 25;106(34):14558-63. doi: 10.1073/pnas.0901870106. Epub 2009 Aug 6.
Fungi produce numerous low molecular weight molecules endowed with a multitude of biological activities. However, mining the full-genome sequences of fungi indicates that their potential to produce secondary metabolites is greatly underestimated. Because most of the biosynthesis gene clusters are silent under laboratory conditions, one of the major challenges is to understand the physiological conditions under which these genes are activated. Thus, we cocultivated the important model fungus Aspergillus nidulans with a collection of 58 soil-dwelling actinomycetes. By microarray analyses of both Aspergillus secondary metabolism and full-genome arrays and Northern blot and quantitative RT-PCR analyses, we demonstrate at the molecular level that a distinct fungal-bacterial interaction leads to the specific activation of fungal secondary metabolism genes. Most surprisingly, dialysis experiments and electron microscopy indicated that an intimate physical interaction of the bacterial and fungal mycelia is required to elicit the specific response. Gene knockout experiments provided evidence that one induced gene cluster codes for the long-sought after polyketide synthase (PKS) required for the biosynthesis of the archetypal polyketide orsellinic acid, the typical lichen metabolite lecanoric acid, and the cathepsin K inhibitors F-9775A and F-9775B. A phylogenetic analysis demonstrates that orthologs of this PKS are widespread in nature in all major fungal groups, including mycobionts of lichens. These results provide evidence of specific interaction among microorganisms belonging to different domains and support the hypothesis that not only diffusible signals but intimate physical interactions contribute to the communication among microorganisms and induction of otherwise silent biosynthesis genes.
真菌能产生众多具有多种生物活性的低分子量分子。然而,对真菌全基因组序列的挖掘表明,它们产生次生代谢产物的潜力被大大低估了。由于大多数生物合成基因簇在实验室条件下是沉默的,主要挑战之一是了解这些基因被激活的生理条件。因此,我们将重要的模式真菌构巢曲霉与58种土壤放线菌进行了共培养。通过对曲霉次生代谢和全基因组阵列的微阵列分析以及Northern印迹和定量RT-PCR分析,我们在分子水平上证明了一种独特的真菌-细菌相互作用会导致真菌次生代谢基因的特异性激活。最令人惊讶的是,透析实验和电子显微镜表明,细菌和真菌菌丝体的紧密物理相互作用是引发特异性反应所必需的。基因敲除实验提供了证据,表明一个诱导基因簇编码了长期以来寻找的聚酮合酶(PKS),该酶是原型聚酮化合物苔色酸、典型地衣代谢产物黑茶渍素以及组织蛋白酶K抑制剂F-9775A和F-9775B生物合成所必需的。系统发育分析表明,这种PKS的直系同源物在包括地衣菌共生体在内的所有主要真菌类群中广泛存在于自然界。这些结果提供了属于不同域的微生物之间特异性相互作用的证据,并支持了这样的假设,即不仅可扩散信号,而且紧密的物理相互作用有助于微生物之间的通讯以及诱导原本沉默的生物合成基因。