Elucidation of the life cycle of the endophytic genus Muscodor and its transfer to Induratia in Induratiaceae fam. nov., based on a polyphasic taxonomic approach

Abstract

Molecular phylogenetic studies of cultures derived from some specimens of plant-inhabiting Sordariomycetes using ITS, LSU, rpb2 and tub2 DNA sequence data revealed close affinities to strains of Muscodor. The taxonomy of this biotechnologically important genus, which exclusively consists of endophytes with sterile mycelia that produce antibiotic volatile secondary metabolites, was based on a rather tentative taxonomic concept. Even though it was accommodated in Xylariaceae, its phylogenetic position had so far remained obscure. Our phylogeny shows that Muscodor species have affinities to the xylarialean genera Emarcea and Induratia, which is corroborated by the fact that their sexual states produce characteristic apiospores. These data allow for the integration of Muscodor in Induratia, i.e. the genus that was historically described first. The multi-locus phylogenetic tree clearly revealed that a clade comprising Emarcea and Induratia forms a monophylum separate from representatives of Xylariaceae, for which we propose the new family Induratiaceae. Divergence time estimations revealed that Induratiaceae has been diverged from the Xylariaceae + Clypeosphaeriaceae clade at 93 (69–119) million years ago (Mya) with the crown age of 61 (39–85) Mya during the Cretaceous period. The ascospore-derived cultures were studied for the production of volatile metabolites, using both, dual cultures for assessment of antimicrobial effects and extensive analyses using gas chromatography coupled with mass spectrometry (GC–MS). The antimicrobial effects observed were significant, but not as strong as in the case of the previous reports on Muscodor species. The GC–MS results give rise to some doubt on the validity of the previous identification of certain volatiles. Many peaks in the GC–MS chromatograms could not be safely identified by database searches and may represent new natural products. The isolation of these compounds by preparative chromatography and their subsequent characterisation by nuclear magnetic resonance (NMR) spectroscopy or total synthesis will allow for a more concise identification of these volatiles, and they should also be checked for their individual contribution to the observed antibiotic effects. This will be an important prerequisite for the development of biocontrol strains.