Comparative volatilomics of coral endosymbionts from one- and comprehensive two-dimensional gas chromatography approaches

Volatilomics, the examination of all biogenic volatile organic compounds (BVOCs) emitted by an organism or system, holds potential as a novel screening tool for taxonomy, fitness, and ecological functioning. Volatilomics has been largely applied to terrestrial environments, but highly productive coastal marine systems, which are major sources of specific BVOCs, such as dimethyl sulfide, have been largely neglected. Volatilomic measurements are highly method-dependent, with different instrumentation impacting the diversity of identified BVOCs—therefore, understanding these biases is critical to reconcile studies. Here, we investigated BVOCs emitted by two species of coral endosymbiotic microalgae (Symbiodinium tridacnidorum and Durusdinium trenchii) using gas chromatography–mass spectrometry (GC–MS) and comprehensive two-dimensional gas chromatography–time-of-flight mass spectrometry (GC × GC–TOFMS). Seven chemical classes were detected by both instruments, the most common being aromatic hydrocarbons. However, GC × GC resolved seven times more BVOCs than GC–MS (290 vs. 40), with a higher proportion of compounds tentatively identified (173 vs. 14). Notably, nine chemical classes were exclusively identified by GC × GC, including alkane, alkene, aldehyde, ester, and nitrile BVOCs—each potentially fulfilling undescribed functions in marine organisms. The microalgal species investigated shared a large proportion of BVOCs, and this result was consistent across instruments (97 and 98% shared compounds via GC × GC and GC–MS, respectively), suggesting consistent retrieval of general patterns between instruments. This method comparison is the first of its kind in marine systems and confirms the greater analytical power of GC × GC, required to help resolve complex BVOC emissions and the identification of their roles in marine systems.