Organisms must have strategies to ensure successful reproduction. Some animals that deposit eggs protect their embryos from fouling/disease with the help of microorganisms. Although beneficial bacteria are hypothesized to contribute to egg defense in some organisms, the mechanisms of this protection remain largely unknown, with the exception of a few recently described systems. Using both experimental and analytical approaches, we demonstrate that symbiotic bacteria associated with a cephalopod reproductive gland and eggs inhibit fungi. Chemical analyses suggest that these bacteria produce antimicrobial compounds that may prevent overgrowth from fungi and other microorganisms. Given the distribution of these symbiotic glands among many cephalopods, similar defensive relationships may be more common in aquatic environments than previously realized. Such defensive symbioses may also be a rich source for the discovery of new antimicrobial compounds.

Sarcophyton glaucum is one of the most abundant and chemically studied soft corals with over 100 natural products reported in the literature, primarily cembrane diterpenoids. Yet, wide variation in the chemistry observed from S. glaucum over the past 50 years has led to its reputation as a capricious producer of bioactive metabolites. Recent molecular phylogenetic analysis revealed that S. glaucum is not a single species but a complex of at least seven genetically distinct species not distinguishable using traditional taxonomic criteria. We hypothesized that perceived intraspecific chemical variation observed in S. glaucum was actually due to differences between cryptic species (interspecific variation). To test this hypothesis, we collected Sarcophyton samples in Palau, performed molecular phylogenetic analysis, and prepared chemical profiles of sample extracts using gas chromatography-flame ionization detection. Both unsupervised (principal component analysis) and supervised (linear discriminant analysis) statistical analyses of these profiles revealed a strong relationship between cryptic species membership and chemical profiles. Liquid chromatography with tandem mass spectrometry-based analysis using feature-based molecular networking permitted identification of the chemical drivers of this difference between clades, including cembranoid diterpenes (2R,11R,12R)-isosarcophytoxide (5), (2S,11R,12R)-isosarcophytoxide (6), and isosarcophine (7). Our results suggest that early chemical studies of Sarcophyton may have unknowingly conflated different cryptic species of S. glaucum, leading to apparently idiosyncratic chemical variation.

Fungus-growing ants depend on a fungal mutualist that can fall prey to fungal pathogens. This mutualist is cultivated by these ants in structures called fungus gardens. Ants exhibit weeding behaviors that keep their garden healthy by physically removing compromised pieces. However, how ants detect diseases of their fungus gardens is unknown. Here, we applied the logic of Koch's postulates using environmental fungal community genomic sequencing, fungal isolation, and in vitro infection experiments to establish Trichoderma spp. as pathogens of Trachymyrmex septentrionalis fungus gardens. Our environmental data showed that Trichoderma are the most abundant non-cultivar fungi in wild T. septentrionalis fungus gardens. We further determined that metabolites produced by Trichoderma induce an ant weeding response that mirrors their response to live Trichoderma. Combining ant behavioral experiments with bioactivity-guided fractionation and statistical prioritization of metabolites in Trichoderma extracts demonstrated that T. septentrionalis ants weed in response to peptaibols, a specific class of secondary metabolites known to be produced by Trichoderma fungi. Similar assays conducted using purified peptaibols, including the two new peptaibols trichokindins VIII and IX, suggested that weeding is likely induced by peptaibols as a class rather than by a single peptaibol metabolite. In addition to their presence in laboratory experiments, we detected peptaibols in wild fungus gardens. Our combination of environmental data and in vitro experiments strongly support that peptaibols act as chemical cues of Trichoderma pathogenesis in T. septentrionalis fungus gardens.

Untargeted metabolomics is a powerful tool for investigating chemistry of complex biological systems, but its utility is compromised by the presence of uninformative features and the limited efficiency of currently available prioritization tools. More effective filtering and prioritization tools are required to address the challenges of large untargeted metabolomics datasets. Here, we introduce Metabolomics Peak Analysis Computational Tool (MPACT), a new mass spectrometry data analysis platform employing filtering based on multiple modalities, statistical techniques incorporating multilevel replication, and interactive data visualization. We demonstrate application of MPACT to uncover hidden effects of the rare earth element cerium on tunicate-associated bacterium Streptomyces sp. PTY087I2, culminating in characterization of two thiolated compounds including a new cysteine derivative, granaticin C, and granaticin D, recently described as mycothiogranaticin A. While we demonstrate application of MPACT to microbial natural products discovery using an elicitation approach, the platform should be readily adaptable to investigation of multipartite interactions, biomarker detection, small molecules in the environment, and a wide range of other complex sample types.

No abstract