Dissecting the microbiome of a polyketide-producing ascidian across the Anvers Island archipelago, Antarctica
Polar marine ecosystems hold the potential for bioactive compound biodiscovery, based on their untapped macro- and microorganismal diversity. Characterization of polar benthic marine invertebrate-associated microbiomes is limited to few studies. This study was motivated by our interest in better understanding the microbiome structure and composition of the ascidian, Synoicum adareanum, in which the bioactive macrolide that has specific activity to melanoma, palmerolide A (PalA), was found. PalA bears structural resemblance to a combined nonribosomal peptide polyketide, that has similarities to microbially-produced macrolides. We conducted a spatial survey to assess both PalA levels and microbiome composition in S. adareanum in a region of the Antarctic Peninsula near Anvers Island (64{degrees} 46'S, 64{degrees} 03'W). PalA was ubiquitous and abundant across a collection of 21 ascidians (3 subsamples each) sampled from seven sites across the Anvers Island archipelago. The microbiome composition (V3-V4 16S rRNA gene sequence variants) of these 63 samples revealed a core suite of 21 bacteria, 20 of which were distinct from regional bacterioplankton. Co-occurrence analysis yielded several potentially interacting subsystems and, although the levels of PalA detected were not found to correlate with specific sequence variants, the core members appeared to occur in a preferred optimum and tolerance range of PalA levels. Taking these results together with an analysis of biosynthetic potential of related microbiome taxa indicates a core microbiome with substantial promise for natural product biosynthesis that likely interact with the host and with each other.