Mass spectrometry imaging of secondary metabolites directly on fungal cultures

Abstract

Desorption electrospray ionization mass spectrometry (DESI-MS) is an ambient ionization technique that enables imaging experiments directly on fungal cultures. Much information can be gained by examining an organism directly from culture, rather than through an extraction process, as the regional and temporal distribution of bioactive compounds can give a better understanding of interactions in the environment. However, this technique has been underutilized towards the direct analysis of fungal cultures. A major challenge of fungal culture analysis with DESI-MS is the requirement of a firm, flat surface for effective ionization. The media upon which fungi grow can be easily deformed by the pressures from the solvent spray and gas, and the fungal topography is naturally uneven, often containing mycelium and spores that move freely. Furthermore, DESI-MS imaging can only analyse the surface of a sample, thus internal compounds remain undetected. This project first sought to overcome these issues, and then, apply the newly developed methodology to explore the chemical interactions between two distinct fungi. To test the methodology, a fungus that produces antifungal metabolites was grown against a mycotoxin producing fungus, both of the phylum Ascomycota. By comparing the spatial and temporal distribution of secondary metabolites between both isolated cultures and co-cultures, the chemical exchanges that took place were visualized.