The Biological Diversity and Production of Volatile Organic Compounds by Stem-Inhabiting Endophytic Fungi of Ecuador.

Susan Rundell,Scott Strobel,Daniel Spakowicz,Alexandra Narváez-Trujillo

doi:10.3390/jof1030384

Abstract

Fungal endophytes colonize every major lineage of land plants without causing apparent harm to their hosts. Despite their production of interesting and potentially novel compounds, endophytes—particularly those inhabiting stem tissues—are still a vastly underexplored component of microbial diversity. In this study, we explored the diversity of over 1500 fungal endophyte isolates collected from three Ecuadorian ecosystems: lowland tropical forest, cloud forest, and coastal dry forest. We sought to determine whether Ecuador’s fungal endophytes are hyperdiverse, and whether that biological diversity is reflected in the endophytes’ chemical diversity. To assess this chemical diversity, we analyzed a subset of isolates for their production of volatile organic compounds (VOCs), a representative class of natural products. This study yielded a total of 1526 fungal ITS sequences comprising some 315 operational taxonomic units (OTUs), resulting in a non-asymptotic OTU accumulation curve and characterized by a Fisher’s α of 120 and a Shannon Diversity score of 7.56. These figures suggest that the Ecuadorian endophytes are hyperdiverse. Furthermore, the 113 isolates screened for VOCs produced more than 140 unique compounds. These results present a mere snapshot of the remarkable biological and chemical diversity of stem-inhabiting endophytic fungi from a single neotropical country.

Highlights

Endophytes are a diverse array of organisms—including fungi and bacteria—that are capable, for at least part of their life cycles, of living within the tissues of living plants without causing any apparent harm to their hosts [1]
A study by Arnold and Lutzoni [4] found that 1403 foliar endophytes isolated from four different latitudinal zones had a Fisher’s α of 103; those endophytes collected from neotropical angiosperms at Barro Colorado Island, Panama, had a Fisher’s α of 31
The results of this study suggest that it is possible, at least in the case of volatile organic compounds (VOCs), for single clades of endophytes to be enriched in certain classes of natural products such as monoterpenoids, perhaps in predictable ways

Summary

Introduction

Endophytes are a diverse array of organisms—including fungi and bacteria—that are capable, for at least part of their life cycles, of living within the tissues of living plants without causing any apparent harm to their hosts [1]. Arnold and Lutzoni [4] found a pattern whereby the diversity of foliar endophytic fungi increased with decreasing latitude They evaluated the diversity of fungal endophytes colonizing the leaves of common plants in arctic, boreal, temperate, and tropical regions, and found the greatest diversity at Barro Colorado Island, Panama [4]. An earlier study on Barro Colorado Island found that residing within 19 trees of two co-occurring species were a total of 242 morphospecies of fungal endophytes [5]. This is likely an underestimate of the true number of morphospecies colonizing these two species of plants alone, given that researchers only counted those endophytes that were readily culturable. As endophytes have received increasing attention, revised estimates have predicted nearly as many fungal endophytes as was once predicted for the entire fungal richness of the world [6,7]

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