AUTHOR=Ugarelli Kelly , Jagels Annika , Choi Chang Jae , Loesgen Sandra , Stingl Ulrich 

TITLE=Fungal endophytes from Thalassia testudinum show bioactivity against the seagrass pathogen, Labyrinthula spp.

JOURNAL=Frontiers in Marine Science

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2024.1359610

DOI=10.3389/fmars.2024.1359610

ISSN=2296-7745

ABSTRACT=<p><italic>Thalassia testudinum</italic> has undergone die-offs in the past century due to seagrass wasting disease caused by <italic>Labyrinthula</italic> sp. Little is known about how seagrasses resist <italic>Labyrinthula</italic> infections, but metabolites that inhibit <italic>Labyrinthula</italic> were previously extracted from seagrass leaves. Furthermore, leaf fungal endophytes from seagrasses possess antipathogenic potential, but their activity against <italic>Labyrinthula</italic> is unknown. Here, we aimed to identify whether fungal endophytes of <italic>T. testudinum</italic> can aid in disease defense against <italic>Labyrinthula</italic>. Through Illumina amplicon sequencing of the leaves’ mycobiome, we identified fungi that are known to produce antimicrobials. We also isolated and extracted organic compounds from endophytes to test their anti-<italic>Labyrinthula</italic> potential using disk diffusion assays. There were 22 isolates that inhibited <italic>Labyrinthula</italic>, from which two isolates, <italic>Trichoderma</italic> sp. P1a and <italic>Diaporthe</italic> sp. M14, displayed strong inhibition. LC-HRMS/MS analysis determined the likely bioactive compounds of <italic>Trichoderma</italic> as peptaibols and of <italic>Diaporthe</italic> as cytosporone B. Cytosporone B was confirmed bioactive against <italic>Labyrinthula </italic>via disk diffusion assays. While these organisms are low in abundance in the mycobiome, this study demonstrates that seagrass endophytes have the potential to play an important role in defense against <italic>Labyrinthula</italic>.</p>