New nematicidal and antimicrobial secondary metabolites from a new species in the new genus, Pseudobambusicola thailandica

Zeljka Rupcic, Clara Chepkirui, Margarita Hernández-Restrepo, Pedro W. Crous, Janet Jennifer Luangsa-ard, Marc Stadler

During the course of a study on the functional biodiversity of the mycobiota inhabiting rainforests in Thailand, a fungal strain was isolated from a plant sample and shown to represent an undescribed species, as inferred from a combination of morphological and molecular phylogenetic methods. Molecular phylogenetic analyses, based on four DNA loci, revealed a phylogenetic tree with the newly generated sequences clustering in a separate branch, together with members of the Sulcatisporaceae (Pleosporales, Ascomycota). The Thai specimen morphologically resembled Neobambusicola strelitziae in having pycnidial conidiomata with phialidic conidiogenous cells that produce both fusoid-ellipsoid macroconidia and subcylindrical microconidia. However, the new fungus, for which the name Pseudobambusicola thailandica is proposed, differs from N. strelitziae in having conidiomata with well-defined necks, the presence of globose to subglobose thick-walled cells adjacent to conidiomata and the production of chlamydospores in culture. When cultures of P. thailandica, growing on water agar, were confronted with Caenorhabditis elegans nematodes, worms approaching the fungal mycelia were killed. This observation gave rise to a study of its secondary metabolites and six novel and two known compounds were isolated from submerged cultures of P. thailandica. The structures of metabolites 1-6, for which the trivial names thailanones A-F are proposed, were elucidated using a combination of spectral methods, including extensive 1 and 2D NMR analysis and high resolution mass spectrometry. Compounds 4 and 8 showed strong nematicidal and weak antifungal activity, whereas all other tested compounds showed moderate to weak nematicidal activity but no significant effects in the serial dilution assay against various fungi and bacteria. Compounds 1 and 8 also inhibited growth of the pathogenic basidiomycete Phellinus tremulae in a plate diffusion assay.