Imaging Mass Spectrometry of a Coral Microbe Interaction with Fungi
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Fungal infections are increasing worldwide, including in the aquatic environment. Microbiota that coexist with marine life can provide protection against fungal infections by secretion of metabolites with antifungal properties. Our laboratory has developed mass spectrometric methodologies with the goal of improving our functional understanding of microbial metabolites and guiding the discovery process of anti-infective agents from natural sources. GA40, a Bacillus amyloliquefaciens strain isolated from an octocoral in Panama, displayed antifungal activity against various terrestrial and marine fungal strains. Using matrix-assisted laser desorption/ionization-imaging mass spectrometry (MALDI-IMS), the molecular species produced by this microbe were visualized in a side-by-side interaction with two representative fungal strains, Aspergillus fumigatus and Aspergillus niger. The visualization was performed directly on the agar without the need for extraction. By evaluating the spatial distributions, relative intensities and m/z values of GA40 secreted metabolites in the fungal interactions and singly grown control colonies, we obtained insight into the antifungal activity of secreted metabolites. Annotation of GA40 metabolites observed in MALDI-IMS was facilitated by MS/MS networking analysis, a mass spectrometric technique that clusters metabolites with similar MS/MS fragmentation patterns. This analysis established that the predominant GA40 metabolites belong to the iturin family. In a fungal inhibition assay of A. fumigatus, the GA40 iturin metabolites were found to be responsible for the antifungal properties of this Bacillus strain.
KeywordsAspergillus fumigatus Aspergillus niger Bacillus amyloliquefaciens Antifungal MALDI-imaging mass spectrometry MS/MS networking Lipopeptide Iturin Muriceopsis bayeriana
We thank the Prof. W. Nierman lab (JCVI) and the Paul Jensen lab (SIO, UCSD) for donation of strains, and Dr. Hector M. Guzman for taxonomical identification of the coral. We acknowledge the Government of Panama (ANAM) for granting permission to make the collections of the coral. This work was supported by NIH AI095125 and S10RR029121, by the NIH Fogarty International Center International Cooperative Biodiversity Groups program TW006634, and by the Government of Panama SENACYT COL09-047 and COL08-061.
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