Probing marine natural product defenses with DESI-imaging mass spectrometry

Abstract

To demonstrate that a toxin or other natural product serves as a predator or pathogen deterrent requires that (i) the defined compound in question have the requisite biological activity, (ii) the compound is present at levels capable of eliciting an effect in the target organism, (iii) there is a physical mechanism for the substance to interact with its target before death of the producer, and (iv) the avoidance behavior in the target organism actually occurs. Although many highly-unique natural products have been defined from the marine environment, and they appear to serve as predator and pathogen deterrents, it has been extremely challenging to establish their quantity and physical location in the producing organism's tissues, thus leaving uncertainty about their true natural function. However, in this issue of PNAS, Lane et al. (1) have used a novel mass spectrometric approach [desorption electrospray ionization (DESI)] (Fig. 1) to sensitively, yet precisely, measure the physical location and quantities of antifungal natural products in the surface tissues of a tropical red alga. This advance, combined with other analytical MS developments as described below, is allowing more definitive identification of the physical location of natural products within biological tissues, cells, or even complex mixed-species assemblages (2, 3) and represents a dramatic technological advance for studying such phenomena.