New Negombata species discovered: latrunculin mystery solved

The Red Sea features a remarkable diversity of marine natural products. Among its coral-reef residents, sponges (phylum Porifera) are recognized as a prolific source of novel secondary metabolites. Taxonomic identification and characterization of sponge phylogeny play a key role in understanding the underlying processes and evolution of such secondary metabolite production in sponges. However, sponge morphological plasticity frequently results in ambiguous taxonomic descriptions, necessitating a multidisciplinary approach in sponge species delimitation. One of the most conspicuous reef sponges in the Red Sea belongs to the genus Negombata, known to produce various bioactive compounds, including the macrolides latrunculin A and B (Lat A and B, respectively). Their alternative presence in N. magnifica was previously suggested to result from different environmental conditions, stress, or seasonality. Here, we hypothesized that this variation found in latrunculin presence derives from the existence of another morph of Negombata. We tested this using an integrative approach comprising morphological and molecular examination, characterization of latrunculin types, and analysis of the microbial community structure. We compared those parameters to other species of Negombata and, in greater depth, to the coexisting species, N. magnifica. Our results indicate that Negombata rotundata sp.nov. produces mainly Lat A, and N. magnifica produces Lat B, regardless of environmental factors. Moreover, the two morphs differ in their morphology, microbiome communities, and 28S rDNA sequence. Our findings emphasize the importance of uncovering sponge identity with respect to their secondary products.