Marine organisms produce a wealth of natural products but in the complex environment of a marine sponge it can be difficult to tell which creature should be given the credit. Now US scientists are trying to solve the mystery by visualising the molecules within intact organisms. 

Pieter Dorrestein from the University of California, San Diego, and colleagues used a mass spectrometry approach to help them to identify potentially important biomolecules from sea creatures such as marine sponges and cyanobacteria. These natural products are an underexploited source of potential drugs, Dorrestein said. 'The compounds show unique chemistries and structures that supersede anything pharmaceutical companies or chemists can design or synthesise.'

The technique used by the team - natural product matrix-assisted laser desorption ionisation imaging (npMALDI-I) - also allows the scientists to pinpoint where exactly these natural products are in the organism. And, since up to 40 per cent of a sponge's mass is thought to be attributed to co-existing organisms, the method could help the scientists to discover which of the organisms are responsible for making the potentially bioactive compounds. 

npMALDI-I can be used to locate natural products (such as yanucamide B shown) in cyanobacteria

The team found that, within a cross-section of a sponge, some of the natural products were localised on the outer edges, while others had a more uniform distribution and others were concentrated in the middle. Given that co-existing micro-organisms tend to populate specific regions of the sponge tissue, explained Dorrestein, the results suggest that the micro-organisms are responsible for at least some of the compounds.  

Margo Haygood, an expert in marine systems at Oregon Health & Science University, Beaverton, US, described the work as a major advance. 'As a biologist I've always wanted to be able to see the chemistry in the complex systems we study,' she said. 'Although we have some beautiful and elegant methods for specific molecules, the virtue of this work is that it is general; any compound, even an unknown one, can be detected and mapped within the sample. There is so much we can learn about the origin and function of secondary metabolites by seeing where they are located. When future advances improve the resolution of the imaging to something comparable to light microscopy, as I think is inevitable, it will be a dream come true.'

Sarah Corcoran