Marine sponges have been a prolific source of unique bioactive compounds that are presumed to act as a deterrent to predation. Many of these compounds have potential therapeutic applications; however, the lack of efficient and sustainable synthetic routes frequently limits clinical development. Here, we describe a metagenomic investigation of Mycale hentscheli, a chemically gifted marine sponge that possesses multiple distinct chemotypes. We applied shotgun metagenomic sequencing, hybrid assembly of short- and long-read data, and metagenomic binning to obtain a comprehensive picture of the microbiome of five specimens, spanning three chemotypes. Our data revealed multiple producing species, each having relatively modest secondary metabolomes, that contribute collectively to the chemical arsenal of the holobiont. We assembled complete genomes for multiple new genera, including two species that produce the cytotoxic polyketides pateamine and mycalamide, as well as a third high-abundance symbiont harboring a proteusin-type biosynthetic pathway that appears to encode a new polytheonamide-like compound. We also identified an additional 188 biosynthetic gene clusters, including a pathway for biosynthesis of peloruside. These results suggest that multiple species cooperatively contribute to defensive symbiosis in M. hentscheli and reveal that the taxonomic diversity of secondary-metabolite-producing sponge symbionts is larger and richer than previously recognized. IMPORTANCE Mycale hentscheli is a marine sponge that is rich in bioactive small molecules. Here, we use direct metagenomic sequencing to elucidate highly complete and contiguous genomes for the major symbiotic bacteria of this sponge. We identify complete biosynthetic pathways for the three potent cytotoxic polyketides which have previously been isolated from M. hentscheli. Remarkably, and in contrast to previous studies of marine sponges, we attribute each of these metabolites to a different producing microbe. We also find that the microbiome of M. hentscheli is stably maintained among individuals, even over long periods of time. Collectively, our data suggest a cooperative mode of defensive symbiosis in which multiple symbiotic bacterial species cooperatively contribute to the defensive chemical arsenal of the holobiont.

No abstract

The skyllamycins are a class of heavily modified, non-ribosomal peptides, first isolated from Streptomyces sp. KY11784. A Streptomyces strain with potent antibiotic activity against Bacillus subtilis was isolated from a sample of the New Zealand lichen Pseudocyphellaria dissimilis. Whole genome sequencing and biosynthetic gene cluster genetic analysis coupled with GNPS LCMS/MS molecular networking revealed that this strain had the capacity to produce skyllamycins, including previously undescribed congeners, and that these were likely the source of the observed biological activity. Guided by the results of the molecular networking, we isolated the previously reported skyllamycins A–C (1–3), along with two new congeners, skyllamycins D (4) and E (5). The structures of these compounds were elucidated using comprehensive 1D and 2D NMR analyses, along with HRESIMS fragmentation experiments. Antibacterial assays revealed that skyllamycin D possessed improved activity against B. subtilis E168 compared to previously reported congeners.

Six new lamellarin sulfates (1–6) were isolated from the methanolic extract of the Pacific tunicate Didemnum ternerratum, collected from the Kingdom of Tonga. Mass spectrometric molecular networking through the GNPS platform was used to target the isolation of 1–6. Planar structures were elucidated through a combination of NMR and MS experiments. Through comparison of experimental and calculated ECD spectra, the absolute configurations of atropisomers 2–5 were determined, with their energetic barriers to racemization also determined computationally. The cytotoxicity of the compounds was tested against the human colon carcinoma cell line HCT-116, where lamellarin D-8-sulfate (5) exhibited moderate activity with an IC50 of 9.7 μM.

Global natural products social (GNPS) molecular networking is a useful tool to categorize chemical space within samples and streamline the discovery of new natural products. Here, we demonstrate its use in chemically profiling the extract of the marine tunicate Synoicum kuranui, comprised of many previously reported rubrolides, for new chemical entities. Within the rubrolide cluster, two masses that did not correspond to previously reported congeners were detected, and, following MS-guided fractionation, led to the isolation of new methylated rubrolides T (3) and (Z/E)–U (4). Both compounds showed strong growth inhibitory activity against the Gram-positive bacteria Bacillus subtilis, with minimum inhibitory concentration (MIC) values of 0.41 and 0.91 μM, respectively.

LCMS analysis of an extract of the New Zealand tunicate Synoicum kuranui showed evidence for numerous new rubrolides. Following a mass spectrometry-guided isolation procedure, new hydrated rubrolides V and W (5 and 6), along with previously reported rubrolide G (3), were isolated and characterized using MS and NMR. The anti-bacterial and cell cytotoxic activity of the compounds were compared to the potent anti-MRSA compound rubrolide A; hydration across the C-5/C-6 bond was shown to abrogate antibacterial activity.

Marine organisms are a valuable source of bioactive natural products, yet bryozoan invertebrates have been relatively understudied. Herein, we report nelliellosides A and B, new secondary metabolites of the Pacific bryozoan Nelliella nelliiformis, found using NMR-guided isolation. Their structures, including absolute configurations, were elucidated using spectroscopic and chromatographic techniques. Total synthesis of the natural products and four analogues was also achieved, in addition to an assessment of their biological activity, especially kinase inhibition.

© 2020 Storey et al. Marine sponges have been a prolific source of unique bioactive compounds that are presumed to act as a deterrent to predation. Many of these compounds have potential therapeutic applications; however, the lack of efficient and sustainable synthetic routes frequently limits clinical development. Here, we describe a metag-enomic investigation of Mycale hentscheli, a chemically gifted marine sponge that pos-sesses multiple distinct chemotypes. We applied shotgun metagenomic sequencing, hybrid assembly of short-and long-read data, and metagenomic binning to obtain a comprehensive picture of the microbiome of five specimens, spanning three chemo-types. Our data revealed multiple producing species, each having relatively modest secondary metabolomes, that contribute collectively to the chemical arsenal of the holo-biont. We assembled complete genomes for multiple new genera, including two species that produce the cytotoxic polyketides pateamine and mycalamide, as well as a third high-abundance symbiont harboring a proteusin-type biosynthetic pathway that appears to encode a new polytheonamide-like compound. We also identified an additional 188 biosynthetic gene clusters, including a pathway for biosynthesis of peloruside. These re-sults suggest that multiple species cooperatively contribute to defensive symbiosis in M. hentscheli and reveal that the taxonomic diversity of secondary-metabolite-producing sponge symbionts is larger and richer than previously recognized. IMPORTANCE Mycale hentscheli is a marine sponge that is rich in bioactive small mol-ecules. Here, we use direct metagenomic sequencing to elucidate highly complete and contiguous genomes for the major symbiotic bacteria of this sponge. We identify complete biosynthetic pathways for the three potent cytotoxic polyketides which have previously been isolated from M. hentscheli. Remarkably, and in contrast to previous studies of marine sponges, we attribute each of these metabolites to a different producing mi-crobe. We also find that the microbiome of M. hentscheli is stably maintained among in-dividuals, even over long periods of time. Collectively, our data suggest a cooperative mode of defensive symbiosis in which multiple symbiotic bacterial species cooperatively contribute to the defensive chemical arsenal of the holobiont.